Refactor to support column families, direct rocksdb access
Expose low-level helpers, fix dialyzer warnings WIP column families and mrdb API Basic functionality in place started adding documentation remove doc/ from .gitignore add doc/* files recognize pre-existing tabs at startup wip: most of the functionality in place (not yet merge ops) wip: adding transaction support wip: add transaction test case (currently dumps core) First draft, mnesia plugin user guide Fix note formatting WIP working on indexing Index iterators, dialyzer, xref fixes open db with optimistic transactions Use rocksdb-1.7.0 Use seanhinde rocksdb patch, enable rollback Call the right transaction_get() function WIP add 'snap_tx' activity type tx restart using mrdb_mutex Fix test suite sync bugs WIP instrumented for debugging WIP working on migration test case Add migration test suite Migration works, subscribe to schema changes WIP fix batch handling Manage separate batches per db_ref Add mrdb:fold/3 Add some docs, erlang_ls config Use seanhinde's rocksdb vsn
This commit is contained in:
Ulf Wiger
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# Mnesia Rocksdb - Rocksdb backend plugin for Mnesia #
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Copyright (c) 2013-21 Klarna AB
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__Authors:__ Ulf Wiger ([`ulf@wiger.net`](mailto:ulf@wiger.net)).
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The Mnesia DBMS, part of Erlang/OTP, supports 'backend plugins', making
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it possible to utilize more capable key-value stores than the `dets`
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module (limited to 2 GB per table). Unfortunately, this support is
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undocumented. Below, some informal documentation for the plugin system
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is provided.
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### <a name="Table_of_Contents">Table of Contents</a> ###
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1. [Usage](#Usage)
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1. [Prerequisites](#Prerequisites)
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1. [Getting started](#Getting_started)
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1. [Special features](#Special_features)
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1. [Customization](#Customization)
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1. [Handling of errors in write operations](#Handling_of_errors_in_write_operations)
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1. [Caveats](#Caveats)
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1. [Mnesia backend plugins](#Mnesia_backend_plugins)
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1. [Background](#Background)
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1. [Design](#Design)
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1. [Mnesia index plugins](#Mnesia_index_plugins)
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1. [Rocksdb](#Rocksdb)
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### <a name="Usage">Usage</a> ###
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#### <a name="Prerequisites">Prerequisites</a> ####
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* rocksdb (included as dependency)
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* sext (included as dependency)
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* Erlang/OTP 21.0 or newer (https://github.com/erlang/otp)
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#### <a name="Getting_started">Getting started</a> ####
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Call `mnesia_rocksdb:register()` immediately after
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starting mnesia.
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Put `{rocksdb_copies, [node()]}` into the table definitions of
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tables you want to be in RocksDB.
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#### <a name="Special_features">Special features</a> ####
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RocksDB tables support efficient selects on _prefix keys_.
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The backend uses the `sext` module (see
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[`https://github.com/uwiger/sext`](https://github.com/uwiger/sext)) for mapping between Erlang terms and the
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binary data stored in the tables. This provides two useful properties:
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* The records are stored in the Erlang term order of their keys.
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* A prefix of a composite key is ordered just before any key for which
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it is a prefix. For example, `{x, '_'}` is a prefix for keys `{x, a}`,`{x, b}` and so on.
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This means that a prefix key identifies the start of the sequence of
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entries whose keys match the prefix. The backend uses this to optimize
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selects on prefix keys.
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### Customization
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RocksDB supports a number of customization options. These can be specified
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by providing a `{Key, Value}` list named `rocksdb_opts` under `user_properties`,
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for example:
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```
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mnesia:create_table(foo, [{rocksdb_copies, [node()]},
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...
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{user_properties,
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[{rocksdb_opts, [{max_open_files, 1024}]}]
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}])
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```
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Consult the [RocksDB documentation](https://github.com/facebook/rocksdb/wiki/Setup-Options-and-Basic-Tuning)
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for information on configuration parameters. Also see the section below on handling write errors.
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The default configuration for tables in `mnesia_rocksdb` is:
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```
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default_open_opts() ->
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[ {create_if_missing, true}
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, {cache_size,
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list_to_integer(get_env_default("ROCKSDB_CACHE_SIZE", "32212254"))}
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, {block_size, 1024}
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, {max_open_files, 100}
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, {write_buffer_size,
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list_to_integer(get_env_default(
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"ROCKSDB_WRITE_BUFFER_SIZE", "4194304"))}
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, {compression,
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list_to_atom(get_env_default("ROCKSDB_COMPRESSION", "true"))}
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, {use_bloomfilter, true}
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].
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```
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It is also possible, for larger databases, to produce a tuning parameter file.
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This is experimental, and mostly copied from `mnesia_leveldb`. Consult the
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source code in `mnesia_rocksdb_tuning.erl` and `mnesia_rocksdb_params.erl`.
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Contributions are welcome.
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#### <a name="Caveats">Caveats</a> ####
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Avoid placing `bag` tables in RocksDB. Although they work, each write
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requires additional reads, causing substantial runtime overheads. There
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are better ways to represent and process bag data (see above about
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_prefix keys_).
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The `mnesia:table_info(T, size)` call always returns zero for RocksDB
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tables. RocksDB itself does not track the number of elements in a table, and
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although it is possible to make the `mnesia_rocksdb` backend maintain a size
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counter, it incurs a high runtime overhead for writes and deletes since it
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forces them to first do a read to check the existence of the key. If you
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depend on having an up to date size count at all times, you need to maintain
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it yourself. If you only need the size occasionally, you may traverse the
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table to count the elements.
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### <a name="Mnesia_backend_plugins">Mnesia backend plugins</a> ###
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#### <a name="Background">Background</a> ####
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Mnesia was initially designed to be a RAM-only DBMS, and Erlang's
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`ets` tables were developed for this purpose. In order to support
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persistence, e.g. for configuration data, a disk-based version of `ets`
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(called `dets`) was created. The `dets` API mimicks the `ets` API,
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and `dets` is quite convenient and fast for (nowadays) small datasets.
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However, using a 32-bit bucket system, it is limited to 2GB of data.
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It also doesn't support ordered sets. When used in Mnesia, dets-based
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tables are called `disc_only_copies`.
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To circumvent these limitations, another table type, called `disc_copies`
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was added. This is a combination of `ets` and `disk_log`, where Mnesia
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periodically snapshots the `ets` data to a log file on disk, and meanwhile
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maintains a log of updates, which can be applied at startup. These tables
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are quite performant (especially on read access), but all data is kept in
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RAM, which can become a serious limitation.
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A backend plugin system was proposed by Ulf Wiger in 2016, and further
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developed with Klarna's support, to finally become included in OTP 19.
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Klarna uses a LevelDb backend, but Aeternity, in 2017, instead chose
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to implement a Rocksdb backend plugin.
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### <a name="Design">Design</a> ###
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As backend plugins were added on a long-since legacy-stable Mnesia,
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they had to conform to the existing code structure. For this reason,
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the plugin callbacks hook into the already present low-level access
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API in the `mnesia_lib` module. As a consequence, backend plugins have
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the same access semantics and granularity as `ets` and `dets`. This
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isn't much of a disadvantage for key-value stores like LevelDb and RocksDB,
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but a more serious issue is that the update part of this API is called
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on _after_ the point of no return. That is, Mnesia does not expect
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these updates to fail, and has no recourse if they do. As an aside,
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this could also happen if a `disc_only_copies` table exceeds the 2 GB
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limit (mnesia will not check it, and `dets` will not complain, but simply
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drop the update.)
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### <a name="Mnesia_index_plugins">Mnesia index plugins</a> ###
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When adding support for backend plugins, index plugins were also added. Unfortunately, they remain undocumented.
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An index plugin can be added in one of two ways:
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1. When creating a schema, provide `{index_plugins, [{Name, Module, Function}]}` options.
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1. Call the function `mnesia_schema:add_index_plugin(Name, Module, Function)`
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`Name` must be an atom wrapped as a 1-tuple, e.g. `{words}`.
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The plugin callback is called as `Module:Function(Table, Pos, Obj)`, where `Pos=={words}` in
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our example. It returns a list of index terms.
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<strong>Example</strong>
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Given the following index plugin implementation:
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```
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-module(words).
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-export([words_f/3]).
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words_f(_,_,Obj) when is_tuple(Obj) ->
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words_(tuple_to_list(Obj)).
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words_(Str) when is_binary(Str) ->
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string:lexemes(Str, [$\s, $\n, [$\r,$\n]]);
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words_(L) when is_list(L) ->
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lists:flatmap(fun words_/1, L);
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words_(_) ->
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[].
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```
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We can register the plugin and use it in table definitions:
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```
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Eshell V12.1.3 (abort with ^G)
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1> mnesia:start().
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ok
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2> mnesia_schema:add_index_plugin({words}, words, words_f).
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{atomic,ok}
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3> mnesia:create_table(i, [{index, [{words}]}]).
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{atomic,ok}
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```
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Note that in this case, we had neither a backend plugin, nor even a persistent schema.
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Index plugins can be used with all table types. The registered indexing function (arity 3) must exist
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as an exported function along the node's code path.
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To see what happens when we insert an object, we can turn on call trace.
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```
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4> dbg:tracer().
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{ok,<0.108.0>}
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5> dbg:tp(words, x).
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{ok,[{matched,nonode@nohost,3},{saved,x}]}
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6> dbg:p(all,[c]).
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{ok,[{matched,nonode@nohost,60}]}
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7> mnesia:dirty_write({i,<<"one two">>, [<<"three">>, <<"four">>]}).
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(<0.84.0>) call words:words_f(i,{words},{i,<<"one two">>,[<<"three">>,<<"four">>]})
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(<0.84.0>) returned from words:words_f/3 -> [<<"one">>,<<"two">>,<<"three">>,
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<<"four">>]
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(<0.84.0>) call words:words_f(i,{words},{i,<<"one two">>,[<<"three">>,<<"four">>]})
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(<0.84.0>) returned from words:words_f/3 -> [<<"one">>,<<"two">>,<<"three">>,
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<<"four">>]
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ok
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8> dbg:ctp('_'), dbg:stop().
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ok
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9> mnesia:dirty_index_read(i, <<"one">>, {words}).
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[{i,<<"one two">>,[<<"three">>,<<"four">>]}]
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```
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(The fact that the indexing function is called twice, seems like a performance bug.)
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We can observe that the indexing callback is able to operate on the whole object.
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It needs to be side-effect free and efficient, since it will be called at least once for each update
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(if an old object exists in the table, the indexing function will be called on it too, before it is
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replaced by the new object.)
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### <a name="Rocksdb">Rocksdb</a> ###
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### <a name="Usage">Usage</a> ###
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## Modules ##
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<table width="100%" border="0" summary="list of modules">
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<tr><td><a href="mnesia_rocksdb.md" class="module">mnesia_rocksdb</a></td></tr>
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<tr><td><a href="mnesia_rocksdb_admin.md" class="module">mnesia_rocksdb_admin</a></td></tr>
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<tr><td><a href="mnesia_rocksdb_app.md" class="module">mnesia_rocksdb_app</a></td></tr>
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<tr><td><a href="mnesia_rocksdb_lib.md" class="module">mnesia_rocksdb_lib</a></td></tr>
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<tr><td><a href="mnesia_rocksdb_params.md" class="module">mnesia_rocksdb_params</a></td></tr>
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<tr><td><a href="mnesia_rocksdb_sup.md" class="module">mnesia_rocksdb_sup</a></td></tr>
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<tr><td><a href="mnesia_rocksdb_tuning.md" class="module">mnesia_rocksdb_tuning</a></td></tr>
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<tr><td><a href="mrdb.md" class="module">mrdb</a></td></tr>
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<tr><td><a href="mrdb_index.md" class="module">mrdb_index</a></td></tr>
|
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<tr><td><a href="mrdb_mutex.md" class="module">mrdb_mutex</a></td></tr>
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<tr><td><a href="mrdb_select.md" class="module">mrdb_select</a></td></tr></table>
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@@ -0,0 +1,5 @@
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%% encoding: UTF-8
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{application,mnesia_rocksdb}.
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{modules,[mnesia_rocksdb,mnesia_rocksdb_admin,mnesia_rocksdb_app,
|
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mnesia_rocksdb_lib,mnesia_rocksdb_params,mnesia_rocksdb_sup,
|
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mnesia_rocksdb_tuning,mrdb,mrdb_index,mrdb_mutex,mrdb_select]}.
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# Module mnesia_rocksdb_admin #
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* [Data Types](#types)
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||||
* [Function Index](#index)
|
||||
* [Function Details](#functions)
|
||||
|
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__Behaviours:__ [`gen_server`](gen_server.md).
|
||||
|
||||
<a name="types"></a>
|
||||
|
||||
## Data Types ##
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-alias">alias()</a> ###
|
||||
|
||||
|
||||
<pre><code>
|
||||
alias() = atom()
|
||||
</code></pre>
|
||||
|
||||
|
||||
|
||||
|
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### <a name="type-backend">backend()</a> ###
|
||||
|
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|
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<pre><code>
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backend() = #{db_ref => <a href="#type-db_ref">db_ref()</a>, cf_info => #{<a href="#type-table">table()</a> => <a href="#type-cf">cf()</a>}}
|
||||
</code></pre>
|
||||
|
||||
|
||||
|
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|
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### <a name="type-cf">cf()</a> ###
|
||||
|
||||
|
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<pre><code>
|
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cf() = <a href="http://www.erlang.org/doc/man/mrdb.html#type-db_ref">mrdb:db_ref()</a>
|
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</code></pre>
|
||||
|
||||
|
||||
|
||||
|
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### <a name="type-db_ref">db_ref()</a> ###
|
||||
|
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|
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<pre><code>
|
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db_ref() = <a href="/home/uwiger/ae/mnesia_rocksdb/_build/default/lib/rocksdb/doc/rocksdb.md#type-db_handle">rocksdb:db_handle()</a>
|
||||
</code></pre>
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-gen_server_noreply">gen_server_noreply()</a> ###
|
||||
|
||||
|
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<pre><code>
|
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gen_server_noreply() = {noreply, <a href="#type-st">st()</a>} | {stop, <a href="#type-reason">reason()</a>, <a href="#type-st">st()</a>}
|
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</code></pre>
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-gen_server_reply">gen_server_reply()</a> ###
|
||||
|
||||
|
||||
<pre><code>
|
||||
gen_server_reply() = {reply, <a href="#type-reply">reply()</a>, <a href="#type-st">st()</a>} | {stop, <a href="#type-reason">reason()</a>, <a href="#type-reply">reply()</a>, <a href="#type-st">st()</a>}
|
||||
</code></pre>
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-properties">properties()</a> ###
|
||||
|
||||
|
||||
<pre><code>
|
||||
properties() = [{atom(), any()}]
|
||||
</code></pre>
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-reason">reason()</a> ###
|
||||
|
||||
|
||||
<pre><code>
|
||||
reason() = any()
|
||||
</code></pre>
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-reply">reply()</a> ###
|
||||
|
||||
|
||||
<pre><code>
|
||||
reply() = any()
|
||||
</code></pre>
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-req">req()</a> ###
|
||||
|
||||
|
||||
<pre><code>
|
||||
req() = {create_table, <a href="#type-table">table()</a>, <a href="#type-properties">properties()</a>} | {delete_table, <a href="#type-table">table()</a>} | {load_table, <a href="#type-table">table()</a>} | {related_resources, <a href="#type-table">table()</a>} | {get_ref, <a href="#type-table">table()</a>} | {add_aliases, [<a href="#type-alias">alias()</a>]} | {write_table_property, <a href="#type-tabname">tabname()</a>, tuple()} | {remove_aliases, [<a href="#type-alias">alias()</a>]} | {migrate, [{<a href="#type-tabname">tabname()</a>, map()}]} | {prep_close, <a href="#type-table">table()</a>} | {close_table, <a href="#type-table">table()</a>}
|
||||
</code></pre>
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-st">st()</a> ###
|
||||
|
||||
|
||||
<pre><code>
|
||||
st() = #st{backends = #{<a href="#type-alias">alias()</a> => <a href="#type-backend">backend()</a>}, standalone = #{{<a href="#type-alias">alias()</a>, <a href="#type-table">table()</a>} => <a href="#type-cf">cf()</a>}, default_opts = [{atom(), term()}]}
|
||||
</code></pre>
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-table">table()</a> ###
|
||||
|
||||
|
||||
<pre><code>
|
||||
table() = <a href="#type-tabname">tabname()</a> | {admin, <a href="#type-alias">alias()</a>} | {<a href="#type-tabname">tabname()</a>, index, any()} | {<a href="#type-tabname">tabname()</a>, retainer, any()}
|
||||
</code></pre>
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-tabname">tabname()</a> ###
|
||||
|
||||
|
||||
<pre><code>
|
||||
tabname() = atom()
|
||||
</code></pre>
|
||||
|
||||
<a name="index"></a>
|
||||
|
||||
## Function Index ##
|
||||
|
||||
|
||||
<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#add_aliases-1">add_aliases/1</a></td><td></td></tr><tr><td valign="top"><a href="#close_table-2">close_table/2</a></td><td></td></tr><tr><td valign="top"><a href="#code_change-3">code_change/3</a></td><td></td></tr><tr><td valign="top"><a href="#create_table-3">create_table/3</a></td><td></td></tr><tr><td valign="top"><a href="#delete_table-2">delete_table/2</a></td><td></td></tr><tr><td valign="top"><a href="#ensure_started-0">ensure_started/0</a></td><td></td></tr><tr><td valign="top"><a href="#get_ref-1">get_ref/1</a></td><td></td></tr><tr><td valign="top"><a href="#get_ref-2">get_ref/2</a></td><td></td></tr><tr><td valign="top"><a href="#handle_call-3">handle_call/3</a></td><td></td></tr><tr><td valign="top"><a href="#handle_cast-2">handle_cast/2</a></td><td></td></tr><tr><td valign="top"><a href="#handle_info-2">handle_info/2</a></td><td></td></tr><tr><td valign="top"><a href="#init-1">init/1</a></td><td></td></tr><tr><td valign="top"><a href="#load_table-2">load_table/2</a></td><td></td></tr><tr><td valign="top"><a href="#meta-0">meta/0</a></td><td></td></tr><tr><td valign="top"><a href="#migrate_standalone-2">migrate_standalone/2</a></td><td></td></tr><tr><td valign="top"><a href="#prep_close-2">prep_close/2</a></td><td></td></tr><tr><td valign="top"><a href="#read_info-1">read_info/1</a></td><td></td></tr><tr><td valign="top"><a href="#read_info-2">read_info/2</a></td><td></td></tr><tr><td valign="top"><a href="#read_info-4">read_info/4</a></td><td></td></tr><tr><td valign="top"><a href="#related_resources-2">related_resources/2</a></td><td></td></tr><tr><td valign="top"><a href="#remove_aliases-1">remove_aliases/1</a></td><td></td></tr><tr><td valign="top"><a href="#request_ref-2">request_ref/2</a></td><td></td></tr><tr><td valign="top"><a href="#start_link-0">start_link/0</a></td><td></td></tr><tr><td valign="top"><a href="#terminate-2">terminate/2</a></td><td></td></tr><tr><td valign="top"><a href="#write_info-4">write_info/4</a></td><td></td></tr><tr><td valign="top"><a href="#write_table_property-3">write_table_property/3</a></td><td></td></tr></table>
|
||||
|
||||
|
||||
<a name="functions"></a>
|
||||
|
||||
## Function Details ##
|
||||
|
||||
<a name="add_aliases-1"></a>
|
||||
|
||||
### add_aliases/1 ###
|
||||
|
||||
`add_aliases(Aliases) -> any()`
|
||||
|
||||
<a name="close_table-2"></a>
|
||||
|
||||
### close_table/2 ###
|
||||
|
||||
`close_table(Alias, Name) -> any()`
|
||||
|
||||
<a name="code_change-3"></a>
|
||||
|
||||
### code_change/3 ###
|
||||
|
||||
`code_change(FromVsn, St, Extra) -> any()`
|
||||
|
||||
<a name="create_table-3"></a>
|
||||
|
||||
### create_table/3 ###
|
||||
|
||||
`create_table(Alias, Name, Props) -> any()`
|
||||
|
||||
<a name="delete_table-2"></a>
|
||||
|
||||
### delete_table/2 ###
|
||||
|
||||
<pre><code>
|
||||
delete_table(Alias::<a href="#type-alias">alias()</a>, Name::<a href="#type-tabname">tabname()</a>) -> ok
|
||||
</code></pre>
|
||||
<br />
|
||||
|
||||
<a name="ensure_started-0"></a>
|
||||
|
||||
### ensure_started/0 ###
|
||||
|
||||
<pre><code>
|
||||
ensure_started() -> ok
|
||||
</code></pre>
|
||||
<br />
|
||||
|
||||
<a name="get_ref-1"></a>
|
||||
|
||||
### get_ref/1 ###
|
||||
|
||||
`get_ref(Name) -> any()`
|
||||
|
||||
<a name="get_ref-2"></a>
|
||||
|
||||
### get_ref/2 ###
|
||||
|
||||
`get_ref(Name, Default) -> any()`
|
||||
|
||||
<a name="handle_call-3"></a>
|
||||
|
||||
### handle_call/3 ###
|
||||
|
||||
<pre><code>
|
||||
handle_call(Req::{<a href="#type-alias">alias()</a>, <a href="#type-req">req()</a>}, From::any(), St::<a href="#type-st">st()</a>) -> <a href="#type-gen_server_reply">gen_server_reply()</a>
|
||||
</code></pre>
|
||||
<br />
|
||||
|
||||
<a name="handle_cast-2"></a>
|
||||
|
||||
### handle_cast/2 ###
|
||||
|
||||
<pre><code>
|
||||
handle_cast(Msg::any(), St::<a href="#type-st">st()</a>) -> <a href="#type-gen_server_noreply">gen_server_noreply()</a>
|
||||
</code></pre>
|
||||
<br />
|
||||
|
||||
<a name="handle_info-2"></a>
|
||||
|
||||
### handle_info/2 ###
|
||||
|
||||
<pre><code>
|
||||
handle_info(Msg::any(), St::<a href="#type-st">st()</a>) -> <a href="#type-gen_server_noreply">gen_server_noreply()</a>
|
||||
</code></pre>
|
||||
<br />
|
||||
|
||||
<a name="init-1"></a>
|
||||
|
||||
### init/1 ###
|
||||
|
||||
`init(X1) -> any()`
|
||||
|
||||
<a name="load_table-2"></a>
|
||||
|
||||
### load_table/2 ###
|
||||
|
||||
`load_table(Alias, Name) -> any()`
|
||||
|
||||
<a name="meta-0"></a>
|
||||
|
||||
### meta/0 ###
|
||||
|
||||
`meta() -> any()`
|
||||
|
||||
<a name="migrate_standalone-2"></a>
|
||||
|
||||
### migrate_standalone/2 ###
|
||||
|
||||
`migrate_standalone(Alias, Tabs) -> any()`
|
||||
|
||||
<a name="prep_close-2"></a>
|
||||
|
||||
### prep_close/2 ###
|
||||
|
||||
`prep_close(Alias, Tab) -> any()`
|
||||
|
||||
<a name="read_info-1"></a>
|
||||
|
||||
### read_info/1 ###
|
||||
|
||||
`read_info(TRec) -> any()`
|
||||
|
||||
<a name="read_info-2"></a>
|
||||
|
||||
### read_info/2 ###
|
||||
|
||||
`read_info(Alias, Tab) -> any()`
|
||||
|
||||
<a name="read_info-4"></a>
|
||||
|
||||
### read_info/4 ###
|
||||
|
||||
`read_info(Alias, Tab, K, Default) -> any()`
|
||||
|
||||
<a name="related_resources-2"></a>
|
||||
|
||||
### related_resources/2 ###
|
||||
|
||||
`related_resources(Alias, Name) -> any()`
|
||||
|
||||
<a name="remove_aliases-1"></a>
|
||||
|
||||
### remove_aliases/1 ###
|
||||
|
||||
`remove_aliases(Aliases) -> any()`
|
||||
|
||||
<a name="request_ref-2"></a>
|
||||
|
||||
### request_ref/2 ###
|
||||
|
||||
`request_ref(Alias, Name) -> any()`
|
||||
|
||||
<a name="start_link-0"></a>
|
||||
|
||||
### start_link/0 ###
|
||||
|
||||
`start_link() -> any()`
|
||||
|
||||
<a name="terminate-2"></a>
|
||||
|
||||
### terminate/2 ###
|
||||
|
||||
`terminate(X1, St) -> any()`
|
||||
|
||||
<a name="write_info-4"></a>
|
||||
|
||||
### write_info/4 ###
|
||||
|
||||
`write_info(Alias, Tab, K, V) -> any()`
|
||||
|
||||
<a name="write_table_property-3"></a>
|
||||
|
||||
### write_table_property/3 ###
|
||||
|
||||
`write_table_property(Alias, Tab, Prop) -> any()`
|
||||
|
||||
@@ -0,0 +1,32 @@
|
||||
|
||||
|
||||
# Module mnesia_rocksdb_app #
|
||||
* [Function Index](#index)
|
||||
* [Function Details](#functions)
|
||||
|
||||
__Behaviours:__ [`application`](application.md).
|
||||
|
||||
<a name="index"></a>
|
||||
|
||||
## Function Index ##
|
||||
|
||||
|
||||
<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#start-2">start/2</a></td><td></td></tr><tr><td valign="top"><a href="#stop-1">stop/1</a></td><td></td></tr></table>
|
||||
|
||||
|
||||
<a name="functions"></a>
|
||||
|
||||
## Function Details ##
|
||||
|
||||
<a name="start-2"></a>
|
||||
|
||||
### start/2 ###
|
||||
|
||||
`start(StartType, StartArgs) -> any()`
|
||||
|
||||
<a name="stop-1"></a>
|
||||
|
||||
### stop/1 ###
|
||||
|
||||
`stop(State) -> any()`
|
||||
|
||||
@@ -0,0 +1,168 @@
|
||||
|
||||
|
||||
# Module mnesia_rocksdb_lib #
|
||||
* [Description](#description)
|
||||
* [Function Index](#index)
|
||||
* [Function Details](#functions)
|
||||
|
||||
RocksDB update wrappers, in separate module for easy tracing and mocking.
|
||||
|
||||
<a name="description"></a>
|
||||
|
||||
## Description ##
|
||||
<a name="index"></a>
|
||||
|
||||
## Function Index ##
|
||||
|
||||
|
||||
<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#check_encoding-2">check_encoding/2</a></td><td></td></tr><tr><td valign="top"><a href="#create_mountpoint-1">create_mountpoint/1</a></td><td></td></tr><tr><td valign="top"><a href="#data_mountpoint-1">data_mountpoint/1</a></td><td></td></tr><tr><td valign="top"><a href="#decode-2">decode/2</a></td><td></td></tr><tr><td valign="top"><a href="#decode_key-1">decode_key/1</a></td><td></td></tr><tr><td valign="top"><a href="#decode_key-2">decode_key/2</a></td><td></td></tr><tr><td valign="top"><a href="#decode_val-1">decode_val/1</a></td><td></td></tr><tr><td valign="top"><a href="#decode_val-3">decode_val/3</a></td><td></td></tr><tr><td valign="top"><a href="#default_encoding-3">default_encoding/3</a></td><td></td></tr><tr><td valign="top"><a href="#delete-3">delete/3</a></td><td></td></tr><tr><td valign="top"><a href="#encode-2">encode/2</a></td><td></td></tr><tr><td valign="top"><a href="#encode_key-1">encode_key/1</a></td><td></td></tr><tr><td valign="top"><a href="#encode_key-2">encode_key/2</a></td><td></td></tr><tr><td valign="top"><a href="#encode_val-1">encode_val/1</a></td><td></td></tr><tr><td valign="top"><a href="#encode_val-2">encode_val/2</a></td><td></td></tr><tr><td valign="top"><a href="#keypos-1">keypos/1</a></td><td></td></tr><tr><td valign="top"><a href="#open_rocksdb-3">open_rocksdb/3</a></td><td></td></tr><tr><td valign="top"><a href="#put-4">put/4</a></td><td></td></tr><tr><td valign="top"><a href="#tabname-1">tabname/1</a></td><td></td></tr><tr><td valign="top"><a href="#valid_key_type-2">valid_key_type/2</a></td><td></td></tr><tr><td valign="top"><a href="#valid_obj_type-2">valid_obj_type/2</a></td><td></td></tr><tr><td valign="top"><a href="#write-3">write/3</a></td><td></td></tr></table>
|
||||
|
||||
|
||||
<a name="functions"></a>
|
||||
|
||||
## Function Details ##
|
||||
|
||||
<a name="check_encoding-2"></a>
|
||||
|
||||
### check_encoding/2 ###
|
||||
|
||||
`check_encoding(Encoding, Attributes) -> any()`
|
||||
|
||||
<a name="create_mountpoint-1"></a>
|
||||
|
||||
### create_mountpoint/1 ###
|
||||
|
||||
`create_mountpoint(Tab) -> any()`
|
||||
|
||||
<a name="data_mountpoint-1"></a>
|
||||
|
||||
### data_mountpoint/1 ###
|
||||
|
||||
`data_mountpoint(Tab) -> any()`
|
||||
|
||||
<a name="decode-2"></a>
|
||||
|
||||
### decode/2 ###
|
||||
|
||||
`decode(Val, X2) -> any()`
|
||||
|
||||
<a name="decode_key-1"></a>
|
||||
|
||||
### decode_key/1 ###
|
||||
|
||||
<pre><code>
|
||||
decode_key(CodedKey::binary()) -> any()
|
||||
</code></pre>
|
||||
<br />
|
||||
|
||||
<a name="decode_key-2"></a>
|
||||
|
||||
### decode_key/2 ###
|
||||
|
||||
`decode_key(CodedKey, Enc) -> any()`
|
||||
|
||||
<a name="decode_val-1"></a>
|
||||
|
||||
### decode_val/1 ###
|
||||
|
||||
<pre><code>
|
||||
decode_val(CodedVal::binary()) -> any()
|
||||
</code></pre>
|
||||
<br />
|
||||
|
||||
<a name="decode_val-3"></a>
|
||||
|
||||
### decode_val/3 ###
|
||||
|
||||
`decode_val(CodedVal, K, Ref) -> any()`
|
||||
|
||||
<a name="default_encoding-3"></a>
|
||||
|
||||
### default_encoding/3 ###
|
||||
|
||||
`default_encoding(X1, Type, As) -> any()`
|
||||
|
||||
<a name="delete-3"></a>
|
||||
|
||||
### delete/3 ###
|
||||
|
||||
`delete(Ref, K, Opts) -> any()`
|
||||
|
||||
<a name="encode-2"></a>
|
||||
|
||||
### encode/2 ###
|
||||
|
||||
`encode(Value, X2) -> any()`
|
||||
|
||||
<a name="encode_key-1"></a>
|
||||
|
||||
### encode_key/1 ###
|
||||
|
||||
<pre><code>
|
||||
encode_key(Key::any()) -> binary()
|
||||
</code></pre>
|
||||
<br />
|
||||
|
||||
<a name="encode_key-2"></a>
|
||||
|
||||
### encode_key/2 ###
|
||||
|
||||
`encode_key(Key, X2) -> any()`
|
||||
|
||||
<a name="encode_val-1"></a>
|
||||
|
||||
### encode_val/1 ###
|
||||
|
||||
<pre><code>
|
||||
encode_val(Val::any()) -> binary()
|
||||
</code></pre>
|
||||
<br />
|
||||
|
||||
<a name="encode_val-2"></a>
|
||||
|
||||
### encode_val/2 ###
|
||||
|
||||
`encode_val(Val, Enc) -> any()`
|
||||
|
||||
<a name="keypos-1"></a>
|
||||
|
||||
### keypos/1 ###
|
||||
|
||||
`keypos(Tab) -> any()`
|
||||
|
||||
<a name="open_rocksdb-3"></a>
|
||||
|
||||
### open_rocksdb/3 ###
|
||||
|
||||
`open_rocksdb(MPd, RdbOpts, CFs) -> any()`
|
||||
|
||||
<a name="put-4"></a>
|
||||
|
||||
### put/4 ###
|
||||
|
||||
`put(Ref, K, V, Opts) -> any()`
|
||||
|
||||
<a name="tabname-1"></a>
|
||||
|
||||
### tabname/1 ###
|
||||
|
||||
`tabname(Tab) -> any()`
|
||||
|
||||
<a name="valid_key_type-2"></a>
|
||||
|
||||
### valid_key_type/2 ###
|
||||
|
||||
`valid_key_type(X1, Key) -> any()`
|
||||
|
||||
<a name="valid_obj_type-2"></a>
|
||||
|
||||
### valid_obj_type/2 ###
|
||||
|
||||
`valid_obj_type(X1, Obj) -> any()`
|
||||
|
||||
<a name="write-3"></a>
|
||||
|
||||
### write/3 ###
|
||||
|
||||
`write(X1, L, Opts) -> any()`
|
||||
|
||||
@@ -0,0 +1,80 @@
|
||||
|
||||
|
||||
# Module mnesia_rocksdb_params #
|
||||
* [Function Index](#index)
|
||||
* [Function Details](#functions)
|
||||
|
||||
__Behaviours:__ [`gen_server`](gen_server.md).
|
||||
|
||||
<a name="index"></a>
|
||||
|
||||
## Function Index ##
|
||||
|
||||
|
||||
<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#code_change-3">code_change/3</a></td><td></td></tr><tr><td valign="top"><a href="#delete-1">delete/1</a></td><td></td></tr><tr><td valign="top"><a href="#handle_call-3">handle_call/3</a></td><td></td></tr><tr><td valign="top"><a href="#handle_cast-2">handle_cast/2</a></td><td></td></tr><tr><td valign="top"><a href="#handle_info-2">handle_info/2</a></td><td></td></tr><tr><td valign="top"><a href="#init-1">init/1</a></td><td></td></tr><tr><td valign="top"><a href="#lookup-2">lookup/2</a></td><td></td></tr><tr><td valign="top"><a href="#start_link-0">start_link/0</a></td><td></td></tr><tr><td valign="top"><a href="#store-2">store/2</a></td><td></td></tr><tr><td valign="top"><a href="#terminate-2">terminate/2</a></td><td></td></tr></table>
|
||||
|
||||
|
||||
<a name="functions"></a>
|
||||
|
||||
## Function Details ##
|
||||
|
||||
<a name="code_change-3"></a>
|
||||
|
||||
### code_change/3 ###
|
||||
|
||||
`code_change(X1, S, X3) -> any()`
|
||||
|
||||
<a name="delete-1"></a>
|
||||
|
||||
### delete/1 ###
|
||||
|
||||
`delete(Tab) -> any()`
|
||||
|
||||
<a name="handle_call-3"></a>
|
||||
|
||||
### handle_call/3 ###
|
||||
|
||||
`handle_call(X1, X2, S) -> any()`
|
||||
|
||||
<a name="handle_cast-2"></a>
|
||||
|
||||
### handle_cast/2 ###
|
||||
|
||||
`handle_cast(X1, S) -> any()`
|
||||
|
||||
<a name="handle_info-2"></a>
|
||||
|
||||
### handle_info/2 ###
|
||||
|
||||
`handle_info(X1, S) -> any()`
|
||||
|
||||
<a name="init-1"></a>
|
||||
|
||||
### init/1 ###
|
||||
|
||||
`init(X1) -> any()`
|
||||
|
||||
<a name="lookup-2"></a>
|
||||
|
||||
### lookup/2 ###
|
||||
|
||||
`lookup(Tab, Default) -> any()`
|
||||
|
||||
<a name="start_link-0"></a>
|
||||
|
||||
### start_link/0 ###
|
||||
|
||||
`start_link() -> any()`
|
||||
|
||||
<a name="store-2"></a>
|
||||
|
||||
### store/2 ###
|
||||
|
||||
`store(Tab, Params) -> any()`
|
||||
|
||||
<a name="terminate-2"></a>
|
||||
|
||||
### terminate/2 ###
|
||||
|
||||
`terminate(X1, X2) -> any()`
|
||||
|
||||
@@ -0,0 +1,32 @@
|
||||
|
||||
|
||||
# Module mnesia_rocksdb_sup #
|
||||
* [Function Index](#index)
|
||||
* [Function Details](#functions)
|
||||
|
||||
__Behaviours:__ [`supervisor`](supervisor.md).
|
||||
|
||||
<a name="index"></a>
|
||||
|
||||
## Function Index ##
|
||||
|
||||
|
||||
<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#init-1">init/1</a></td><td></td></tr><tr><td valign="top"><a href="#start_link-0">start_link/0</a></td><td></td></tr></table>
|
||||
|
||||
|
||||
<a name="functions"></a>
|
||||
|
||||
## Function Details ##
|
||||
|
||||
<a name="init-1"></a>
|
||||
|
||||
### init/1 ###
|
||||
|
||||
`init(X1) -> any()`
|
||||
|
||||
<a name="start_link-0"></a>
|
||||
|
||||
### start_link/0 ###
|
||||
|
||||
`start_link() -> any()`
|
||||
|
||||
@@ -0,0 +1,126 @@
|
||||
|
||||
|
||||
# Module mnesia_rocksdb_tuning #
|
||||
* [Function Index](#index)
|
||||
* [Function Details](#functions)
|
||||
|
||||
<a name="index"></a>
|
||||
|
||||
## Function Index ##
|
||||
|
||||
|
||||
<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#cache-1">cache/1</a></td><td></td></tr><tr><td valign="top"><a href="#calc_sizes-0">calc_sizes/0</a></td><td></td></tr><tr><td valign="top"><a href="#calc_sizes-1">calc_sizes/1</a></td><td></td></tr><tr><td valign="top"><a href="#count_rdb_tabs-0">count_rdb_tabs/0</a></td><td></td></tr><tr><td valign="top"><a href="#count_rdb_tabs-1">count_rdb_tabs/1</a></td><td></td></tr><tr><td valign="top"><a href="#default-1">default/1</a></td><td></td></tr><tr><td valign="top"><a href="#describe_env-0">describe_env/0</a></td><td></td></tr><tr><td valign="top"><a href="#get_avail_ram-0">get_avail_ram/0</a></td><td></td></tr><tr><td valign="top"><a href="#get_maxfiles-0">get_maxfiles/0</a></td><td></td></tr><tr><td valign="top"><a href="#get_maxfiles-1">get_maxfiles/1</a></td><td></td></tr><tr><td valign="top"><a href="#ideal_max_files-0">ideal_max_files/0</a></td><td></td></tr><tr><td valign="top"><a href="#ideal_max_files-1">ideal_max_files/1</a></td><td></td></tr><tr><td valign="top"><a href="#max_files-1">max_files/1</a></td><td></td></tr><tr><td valign="top"><a href="#rdb_indexes-0">rdb_indexes/0</a></td><td></td></tr><tr><td valign="top"><a href="#rdb_indexes-1">rdb_indexes/1</a></td><td></td></tr><tr><td valign="top"><a href="#rdb_tabs-0">rdb_tabs/0</a></td><td></td></tr><tr><td valign="top"><a href="#rdb_tabs-1">rdb_tabs/1</a></td><td></td></tr><tr><td valign="top"><a href="#write_buffer-1">write_buffer/1</a></td><td></td></tr></table>
|
||||
|
||||
|
||||
<a name="functions"></a>
|
||||
|
||||
## Function Details ##
|
||||
|
||||
<a name="cache-1"></a>
|
||||
|
||||
### cache/1 ###
|
||||
|
||||
`cache(X1) -> any()`
|
||||
|
||||
<a name="calc_sizes-0"></a>
|
||||
|
||||
### calc_sizes/0 ###
|
||||
|
||||
`calc_sizes() -> any()`
|
||||
|
||||
<a name="calc_sizes-1"></a>
|
||||
|
||||
### calc_sizes/1 ###
|
||||
|
||||
`calc_sizes(D) -> any()`
|
||||
|
||||
<a name="count_rdb_tabs-0"></a>
|
||||
|
||||
### count_rdb_tabs/0 ###
|
||||
|
||||
`count_rdb_tabs() -> any()`
|
||||
|
||||
<a name="count_rdb_tabs-1"></a>
|
||||
|
||||
### count_rdb_tabs/1 ###
|
||||
|
||||
`count_rdb_tabs(Db) -> any()`
|
||||
|
||||
<a name="default-1"></a>
|
||||
|
||||
### default/1 ###
|
||||
|
||||
`default(X1) -> any()`
|
||||
|
||||
<a name="describe_env-0"></a>
|
||||
|
||||
### describe_env/0 ###
|
||||
|
||||
`describe_env() -> any()`
|
||||
|
||||
<a name="get_avail_ram-0"></a>
|
||||
|
||||
### get_avail_ram/0 ###
|
||||
|
||||
`get_avail_ram() -> any()`
|
||||
|
||||
<a name="get_maxfiles-0"></a>
|
||||
|
||||
### get_maxfiles/0 ###
|
||||
|
||||
`get_maxfiles() -> any()`
|
||||
|
||||
<a name="get_maxfiles-1"></a>
|
||||
|
||||
### get_maxfiles/1 ###
|
||||
|
||||
`get_maxfiles(X1) -> any()`
|
||||
|
||||
<a name="ideal_max_files-0"></a>
|
||||
|
||||
### ideal_max_files/0 ###
|
||||
|
||||
`ideal_max_files() -> any()`
|
||||
|
||||
<a name="ideal_max_files-1"></a>
|
||||
|
||||
### ideal_max_files/1 ###
|
||||
|
||||
`ideal_max_files(D) -> any()`
|
||||
|
||||
<a name="max_files-1"></a>
|
||||
|
||||
### max_files/1 ###
|
||||
|
||||
`max_files(X1) -> any()`
|
||||
|
||||
<a name="rdb_indexes-0"></a>
|
||||
|
||||
### rdb_indexes/0 ###
|
||||
|
||||
`rdb_indexes() -> any()`
|
||||
|
||||
<a name="rdb_indexes-1"></a>
|
||||
|
||||
### rdb_indexes/1 ###
|
||||
|
||||
`rdb_indexes(Db) -> any()`
|
||||
|
||||
<a name="rdb_tabs-0"></a>
|
||||
|
||||
### rdb_tabs/0 ###
|
||||
|
||||
`rdb_tabs() -> any()`
|
||||
|
||||
<a name="rdb_tabs-1"></a>
|
||||
|
||||
### rdb_tabs/1 ###
|
||||
|
||||
`rdb_tabs(Db) -> any()`
|
||||
|
||||
<a name="write_buffer-1"></a>
|
||||
|
||||
### write_buffer/1 ###
|
||||
|
||||
`write_buffer(X1) -> any()`
|
||||
|
||||
+943
File diff suppressed because one or more lines are too long
@@ -0,0 +1,99 @@
|
||||
|
||||
|
||||
# Module mrdb_index #
|
||||
* [Data Types](#types)
|
||||
* [Function Index](#index)
|
||||
* [Function Details](#functions)
|
||||
|
||||
<a name="types"></a>
|
||||
|
||||
## Data Types ##
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-index_value">index_value()</a> ###
|
||||
|
||||
|
||||
<pre><code>
|
||||
index_value() = any()
|
||||
</code></pre>
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-iterator_action">iterator_action()</a> ###
|
||||
|
||||
|
||||
<pre><code>
|
||||
iterator_action() = <a href="http://www.erlang.org/doc/man/mrdb.html#type-iterator_action">mrdb:iterator_action()</a>
|
||||
</code></pre>
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-ix_iterator">ix_iterator()</a> ###
|
||||
|
||||
|
||||
<pre><code>
|
||||
ix_iterator() = #mrdb_ix_iter{i = <a href="http://www.erlang.org/doc/man/mrdb.html#type-iterator">mrdb:iterator()</a>, type = set | bag, sub = <a href="http://www.erlang.org/doc/man/mrdb.html#type-ref">mrdb:ref()</a> | pid()}
|
||||
</code></pre>
|
||||
|
||||
|
||||
|
||||
|
||||
### <a name="type-object">object()</a> ###
|
||||
|
||||
|
||||
<pre><code>
|
||||
object() = tuple()
|
||||
</code></pre>
|
||||
|
||||
<a name="index"></a>
|
||||
|
||||
## Function Index ##
|
||||
|
||||
|
||||
<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#iterator-2">iterator/2</a></td><td></td></tr><tr><td valign="top"><a href="#iterator_close-1">iterator_close/1</a></td><td></td></tr><tr><td valign="top"><a href="#iterator_move-2">iterator_move/2</a></td><td></td></tr><tr><td valign="top"><a href="#with_iterator-3">with_iterator/3</a></td><td></td></tr></table>
|
||||
|
||||
|
||||
<a name="functions"></a>
|
||||
|
||||
## Function Details ##
|
||||
|
||||
<a name="iterator-2"></a>
|
||||
|
||||
### iterator/2 ###
|
||||
|
||||
<pre><code>
|
||||
iterator(Tab::<a href="http://www.erlang.org/doc/man/mrdb.html#type-ref_or_tab">mrdb:ref_or_tab()</a>, IxPos::<a href="http://www.erlang.org/doc/man/mrdb.html#type-index_position">mrdb:index_position()</a>) -> {ok, <a href="#type-ix_iterator">ix_iterator()</a>} | {error, term()}
|
||||
</code></pre>
|
||||
<br />
|
||||
|
||||
<a name="iterator_close-1"></a>
|
||||
|
||||
### iterator_close/1 ###
|
||||
|
||||
<pre><code>
|
||||
iterator_close(Mrdb_ix_iter::<a href="#type-ix_iterator">ix_iterator()</a>) -> ok
|
||||
</code></pre>
|
||||
<br />
|
||||
|
||||
<a name="iterator_move-2"></a>
|
||||
|
||||
### iterator_move/2 ###
|
||||
|
||||
<pre><code>
|
||||
iterator_move(Mrdb_ix_iter::<a href="#type-ix_iterator">ix_iterator()</a>, Dir::<a href="#type-iterator_action">iterator_action()</a>) -> {ok, <a href="#type-index_value">index_value()</a>, <a href="#type-object">object()</a>} | {error, term()}
|
||||
</code></pre>
|
||||
<br />
|
||||
|
||||
<a name="with_iterator-3"></a>
|
||||
|
||||
### with_iterator/3 ###
|
||||
|
||||
<pre><code>
|
||||
with_iterator(Tab::<a href="http://www.erlang.org/doc/man/mrdb.html#type-ref_or_tab">mrdb:ref_or_tab()</a>, IxPos::<a href="http://www.erlang.org/doc/man/mrdb.html#type-index_position">mrdb:index_position()</a>, Fun::fun((<a href="#type-ix_iterator">ix_iterator()</a>) -> Res)) -> Res
|
||||
</code></pre>
|
||||
<br />
|
||||
|
||||
@@ -0,0 +1,30 @@
|
||||
|
||||
|
||||
# Module mrdb_mutex #
|
||||
* [Function Index](#index)
|
||||
* [Function Details](#functions)
|
||||
|
||||
<a name="index"></a>
|
||||
|
||||
## Function Index ##
|
||||
|
||||
|
||||
<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#do-2">do/2</a></td><td></td></tr><tr><td valign="top"><a href="#ensure_tab-0">ensure_tab/0</a></td><td></td></tr></table>
|
||||
|
||||
|
||||
<a name="functions"></a>
|
||||
|
||||
## Function Details ##
|
||||
|
||||
<a name="do-2"></a>
|
||||
|
||||
### do/2 ###
|
||||
|
||||
`do(Rsrc, F) -> any()`
|
||||
|
||||
<a name="ensure_tab-0"></a>
|
||||
|
||||
### ensure_tab/0 ###
|
||||
|
||||
`ensure_tab() -> any()`
|
||||
|
||||
@@ -0,0 +1,48 @@
|
||||
|
||||
|
||||
# Module mrdb_select #
|
||||
* [Function Index](#index)
|
||||
* [Function Details](#functions)
|
||||
|
||||
<a name="index"></a>
|
||||
|
||||
## Function Index ##
|
||||
|
||||
|
||||
<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#fold-5">fold/5</a></td><td></td></tr><tr><td valign="top"><a href="#rdb_fold-5">rdb_fold/5</a></td><td></td></tr><tr><td valign="top"><a href="#select-1">select/1</a></td><td></td></tr><tr><td valign="top"><a href="#select-3">select/3</a></td><td></td></tr><tr><td valign="top"><a href="#select-4">select/4</a></td><td></td></tr></table>
|
||||
|
||||
|
||||
<a name="functions"></a>
|
||||
|
||||
## Function Details ##
|
||||
|
||||
<a name="fold-5"></a>
|
||||
|
||||
### fold/5 ###
|
||||
|
||||
`fold(Ref, Fun, Acc, MS, Limit) -> any()`
|
||||
|
||||
<a name="rdb_fold-5"></a>
|
||||
|
||||
### rdb_fold/5 ###
|
||||
|
||||
`rdb_fold(Ref, Fun, Acc, Prefix, Limit) -> any()`
|
||||
|
||||
<a name="select-1"></a>
|
||||
|
||||
### select/1 ###
|
||||
|
||||
`select(Cont) -> any()`
|
||||
|
||||
<a name="select-3"></a>
|
||||
|
||||
### select/3 ###
|
||||
|
||||
`select(Ref, MS, Limit) -> any()`
|
||||
|
||||
<a name="select-4"></a>
|
||||
|
||||
### select/4 ###
|
||||
|
||||
`select(Ref, MS, AccKeys, Limit) -> any()`
|
||||
|
||||
@@ -0,0 +1,250 @@
|
||||
@author Ulf Wiger <ulf@wiger.net>
|
||||
@copyright 2013-21 Klarna AB
|
||||
@title Mnesia Rocksdb - Rocksdb backend plugin for Mnesia
|
||||
|
||||
@doc
|
||||
|
||||
The Mnesia DBMS, part of Erlang/OTP, supports 'backend plugins', making
|
||||
it possible to utilize more capable key-value stores than the `dets'
|
||||
module (limited to 2 GB per table). Unfortunately, this support is
|
||||
undocumented. Below, some informal documentation for the plugin system
|
||||
is provided.
|
||||
|
||||
== Table of Contents ==
|
||||
<ol>
|
||||
<li>{@section Usage}</li>
|
||||
<ol>
|
||||
<li>{@section Prerequisites}</li>
|
||||
<li>{@section Getting started}</li>
|
||||
<li>{@section Special features}</li>
|
||||
<li>{@section Customization}</li>
|
||||
<li>{@section Handling of errors in write operations}</li>
|
||||
<li>{@section Caveats}</li>
|
||||
</ol>
|
||||
<li>{@section Mnesia backend plugins}</li>
|
||||
<ol>
|
||||
<li>{@section Background}</li>
|
||||
<li>{@section Design}</li>
|
||||
</ol>
|
||||
<li>{@section Mnesia index plugins}</li>
|
||||
<li>{@section Rocksdb}</li>
|
||||
</ol>
|
||||
|
||||
== Usage ==
|
||||
|
||||
=== Prerequisites ===
|
||||
|
||||
<ul>
|
||||
<li>rocksdb (included as dependency)</li>
|
||||
<li>sext (included as dependency)</li>
|
||||
<li>Erlang/OTP 21.0 or newer (https://github.com/erlang/otp)</li>
|
||||
</ul>
|
||||
|
||||
=== Getting started ===
|
||||
|
||||
Call `mnesia_rocksdb:register()' immediately after
|
||||
starting mnesia.
|
||||
|
||||
Put `{rocksdb_copies, [node()]}' into the table definitions of
|
||||
tables you want to be in RocksDB.
|
||||
|
||||
=== Special features ===
|
||||
|
||||
RocksDB tables support efficient selects on <em>prefix keys</em>.
|
||||
|
||||
The backend uses the `sext' module (see
|
||||
[https://github.com/uwiger/sext]) for mapping between Erlang terms and the
|
||||
binary data stored in the tables. This provides two useful properties:
|
||||
|
||||
<ul>
|
||||
<li>The records are stored in the Erlang term order of their keys.</li>
|
||||
<li>A prefix of a composite key is ordered just before any key for which
|
||||
it is a prefix. For example, ``{x, '_'}'' is a prefix for keys `{x, a}',
|
||||
`{x, b}' and so on.</li>
|
||||
</ul>
|
||||
|
||||
This means that a prefix key identifies the start of the sequence of
|
||||
entries whose keys match the prefix. The backend uses this to optimize
|
||||
selects on prefix keys.
|
||||
|
||||
### Customization
|
||||
|
||||
RocksDB supports a number of customization options. These can be specified
|
||||
by providing a `{Key, Value}' list named `rocksdb_opts' under `user_properties',
|
||||
for example:
|
||||
|
||||
```
|
||||
mnesia:create_table(foo, [{rocksdb_copies, [node()]},
|
||||
...
|
||||
{user_properties,
|
||||
[{rocksdb_opts, [{max_open_files, 1024}]}]
|
||||
}])
|
||||
'''
|
||||
|
||||
Consult the <a href="https://github.com/facebook/rocksdb/wiki/Setup-Options-and-Basic-Tuning">RocksDB documentation</a>
|
||||
for information on configuration parameters. Also see the section below on handling write errors.
|
||||
|
||||
The default configuration for tables in `mnesia_rocksdb' is:
|
||||
```
|
||||
default_open_opts() ->
|
||||
[ {create_if_missing, true}
|
||||
, {cache_size,
|
||||
list_to_integer(get_env_default("ROCKSDB_CACHE_SIZE", "32212254"))}
|
||||
, {block_size, 1024}
|
||||
, {max_open_files, 100}
|
||||
, {write_buffer_size,
|
||||
list_to_integer(get_env_default(
|
||||
"ROCKSDB_WRITE_BUFFER_SIZE", "4194304"))}
|
||||
, {compression,
|
||||
list_to_atom(get_env_default("ROCKSDB_COMPRESSION", "true"))}
|
||||
, {use_bloomfilter, true}
|
||||
].
|
||||
'''
|
||||
|
||||
It is also possible, for larger databases, to produce a tuning parameter file.
|
||||
This is experimental, and mostly copied from `mnesia_leveldb'. Consult the
|
||||
source code in `mnesia_rocksdb_tuning.erl' and `mnesia_rocksdb_params.erl'.
|
||||
Contributions are welcome.
|
||||
|
||||
=== Caveats ===
|
||||
|
||||
Avoid placing `bag' tables in RocksDB. Although they work, each write
|
||||
requires additional reads, causing substantial runtime overheads. There
|
||||
are better ways to represent and process bag data (see above about
|
||||
<em>prefix keys</em>).
|
||||
|
||||
The `mnesia:table_info(T, size)' call always returns zero for RocksDB
|
||||
tables. RocksDB itself does not track the number of elements in a table, and
|
||||
although it is possible to make the `mnesia_rocksdb' backend maintain a size
|
||||
counter, it incurs a high runtime overhead for writes and deletes since it
|
||||
forces them to first do a read to check the existence of the key. If you
|
||||
depend on having an up to date size count at all times, you need to maintain
|
||||
it yourself. If you only need the size occasionally, you may traverse the
|
||||
table to count the elements.
|
||||
|
||||
== Mnesia backend plugins ==
|
||||
|
||||
=== Background ===
|
||||
|
||||
Mnesia was initially designed to be a RAM-only DBMS, and Erlang's
|
||||
`ets' tables were developed for this purpose. In order to support
|
||||
persistence, e.g. for configuration data, a disk-based version of `ets'
|
||||
(called `dets') was created. The `dets' API mimicks the `ets' API,
|
||||
and `dets' is quite convenient and fast for (nowadays) small datasets.
|
||||
However, using a 32-bit bucket system, it is limited to 2GB of data.
|
||||
It also doesn't support ordered sets. When used in Mnesia, dets-based
|
||||
tables are called `disc_only_copies'.
|
||||
|
||||
To circumvent these limitations, another table type, called `disc_copies'
|
||||
was added. This is a combination of `ets' and `disk_log', where Mnesia
|
||||
periodically snapshots the `ets' data to a log file on disk, and meanwhile
|
||||
maintains a log of updates, which can be applied at startup. These tables
|
||||
are quite performant (especially on read access), but all data is kept in
|
||||
RAM, which can become a serious limitation.
|
||||
|
||||
A backend plugin system was proposed by Ulf Wiger in 2016, and further
|
||||
developed with Klarna's support, to finally become included in OTP 19.
|
||||
Klarna uses a LevelDb backend, but Aeternity, in 2017, instead chose
|
||||
to implement a Rocksdb backend plugin.
|
||||
|
||||
== Design ==
|
||||
|
||||
As backend plugins were added on a long-since legacy-stable Mnesia,
|
||||
they had to conform to the existing code structure. For this reason,
|
||||
the plugin callbacks hook into the already present low-level access
|
||||
API in the `mnesia_lib' module. As a consequence, backend plugins have
|
||||
the same access semantics and granularity as `ets' and `dets'. This
|
||||
isn't much of a disadvantage for key-value stores like LevelDb and RocksDB,
|
||||
but a more serious issue is that the update part of this API is called
|
||||
on <em>after</em> the point of no return. That is, Mnesia does not expect
|
||||
these updates to fail, and has no recourse if they do. As an aside,
|
||||
this could also happen if a `disc_only_copies' table exceeds the 2 GB
|
||||
limit (mnesia will not check it, and `dets' will not complain, but simply
|
||||
drop the update.)
|
||||
|
||||
== Mnesia index plugins ==
|
||||
|
||||
When adding support for backend plugins, index plugins were also added. Unfortunately, they remain undocumented.
|
||||
|
||||
An index plugin can be added in one of two ways:
|
||||
|
||||
<ol>
|
||||
<li>When creating a schema, provide `{index_plugins, [{Name, Module, Function}]}' options.</li>
|
||||
<li>Call the function `mnesia_schema:add_index_plugin(Name, Module, Function)'</li>
|
||||
</ol>
|
||||
|
||||
`Name' must be an atom wrapped as a 1-tuple, e.g. `{words}'.
|
||||
|
||||
The plugin callback is called as `Module:Function(Table, Pos, Obj)', where `Pos=={words}' in
|
||||
our example. It returns a list of index terms.
|
||||
|
||||
<strong>Example</strong>
|
||||
|
||||
Given the following index plugin implementation:
|
||||
|
||||
```
|
||||
-module(words).
|
||||
-export([words_f/3]).
|
||||
|
||||
words_f(_,_,Obj) when is_tuple(Obj) ->
|
||||
words_(tuple_to_list(Obj)).
|
||||
|
||||
words_(Str) when is_binary(Str) ->
|
||||
string:lexemes(Str, [$\s, $\n, [$\r,$\n]]);
|
||||
words_(L) when is_list(L) ->
|
||||
lists:flatmap(fun words_/1, L);
|
||||
words_(_) ->
|
||||
[].
|
||||
'''
|
||||
|
||||
We can register the plugin and use it in table definitions:
|
||||
|
||||
```
|
||||
Eshell V12.1.3 (abort with ^G)
|
||||
1> mnesia:start().
|
||||
ok
|
||||
2> mnesia_schema:add_index_plugin({words}, words, words_f).
|
||||
{atomic,ok}
|
||||
3> mnesia:create_table(i, [{index, [{words}]}]).
|
||||
{atomic,ok}
|
||||
'''
|
||||
|
||||
Note that in this case, we had neither a backend plugin, nor even a persistent schema.
|
||||
Index plugins can be used with all table types. The registered indexing function (arity 3) must exist
|
||||
as an exported function along the node's code path.
|
||||
|
||||
To see what happens when we insert an object, we can turn on call trace.
|
||||
|
||||
```
|
||||
4> dbg:tracer().
|
||||
{ok,<0.108.0>}
|
||||
5> dbg:tp(words, x).
|
||||
{ok,[{matched,nonode@nohost,3},{saved,x}]}
|
||||
6> dbg:p(all,[c]).
|
||||
{ok,[{matched,nonode@nohost,60}]}
|
||||
7> mnesia:dirty_write({i,<<"one two">>, [<<"three">>, <<"four">>]}).
|
||||
(<0.84.0>) call words:words_f(i,{words},{i,<<"one two">>,[<<"three">>,<<"four">>]})
|
||||
(<0.84.0>) returned from words:words_f/3 -> [<<"one">>,<<"two">>,<<"three">>,
|
||||
<<"four">>]
|
||||
(<0.84.0>) call words:words_f(i,{words},{i,<<"one two">>,[<<"three">>,<<"four">>]})
|
||||
(<0.84.0>) returned from words:words_f/3 -> [<<"one">>,<<"two">>,<<"three">>,
|
||||
<<"four">>]
|
||||
ok
|
||||
8> dbg:ctp('_'), dbg:stop().
|
||||
ok
|
||||
9> mnesia:dirty_index_read(i, <<"one">>, {words}).
|
||||
[{i,<<"one two">>,[<<"three">>,<<"four">>]}]
|
||||
'''
|
||||
|
||||
(The fact that the indexing function is called twice, seems like a performance bug.)
|
||||
|
||||
We can observe that the indexing callback is able to operate on the whole object.
|
||||
It needs to be side-effect free and efficient, since it will be called at least once for each update
|
||||
(if an old object exists in the table, the indexing function will be called on it too, before it is
|
||||
replaced by the new object.)
|
||||
|
||||
== Rocksdb ==
|
||||
|
||||
== Usage ==
|
||||
|
||||
@end
|
||||
@@ -0,0 +1,300 @@
|
||||
|
||||
|
||||
# Using Mnesia Plugins #
|
||||
|
||||
Copyright (c) 2017-21 Aeternity Anstalt. All Rights Reserved.
|
||||
|
||||
__Authors:__ Ulf Wiger ([`ulf@wiger.net`](mailto:ulf@wiger.net)).
|
||||
|
||||
The Mnesia DBMS, part of Erlang/OTP, supports 'backend plugins', making
|
||||
it possible to utilize more capable key-value stores than the `dets`
|
||||
module (limited to 2 GB per table). Unfortunately, this support is
|
||||
undocumented. Below, some informal documentation for the plugin system
|
||||
is provided.
|
||||
|
||||
This user guide illustrates these concepts using `mnesia_rocksdb`
|
||||
as an example.
|
||||
|
||||
We will deal with two types of plugin:
|
||||
1. backend plugins
|
||||
2. index plugins
|
||||
|
||||
A backend plugin is a module that implements a `mnesia_backend_type`
|
||||
behavior. Each plugin can support any number of `aliases`, which
|
||||
combined with the plugin module make up a `backend_type`.
|
||||
|
||||
When using `mnesia_rocksdb`, the default alias is `rocksdb_copies`,
|
||||
and it is registered as a `{rocksdb_copies, mnesia_rocksdb}` pair.
|
||||
Once registered, the alias can be used just like the built-in
|
||||
backend types `ram_copies`, `disc_copies`, `disc_only_copies`.
|
||||
Mnesia asks the plugin module which one of the built-in types'
|
||||
semantics the new type is supposed to mimick: ram-only, ram+disk
|
||||
or disk-only. This is mainly relevant for how Mnesia checkpoints and
|
||||
backs up data.
|
||||
|
||||
### <a name="Table_of_Contents">Table of Contents</a> ###
|
||||
|
||||
1. [Usage](#Usage)
|
||||
1. [Prerequisites](#Prerequisites)
|
||||
2. [Getting started](#Getting_started)
|
||||
3. [New indexing functionality](#New_indexing_functionality)
|
||||
|
||||
## Usage
|
||||
|
||||
### Prerequisites
|
||||
|
||||
- rocksdb (included as dependency)
|
||||
- sext (included as dependency)
|
||||
- Erlang/OTP 22.0 or newer (https://github.com/erlang/otp)
|
||||
|
||||
### Getting started
|
||||
|
||||
For the purposes of this user guide, we assume an unnamed, single node
|
||||
mnesia installation. The only place where plugins are affected by
|
||||
distributed Mnesia, is in the table sync callbacks. The simplest way
|
||||
to get all paths in order for experimentation is to check out
|
||||
`mnesia_rocksdb`, building it, and then calling `rebar3 shell`. Unless
|
||||
we note otherwise, this is how a node has been started for each example.
|
||||
|
||||
> Erlang shell interactions have been slightly beautified by eliding
|
||||
> some text and breaking and indenting some lines
|
||||
|
||||
#### Adding a backend type to mnesia
|
||||
|
||||
There are three different ways, all undocumented, to register a
|
||||
backend plugin in mnesia:
|
||||
|
||||
1. Add a `backend_types` option when creating the schema, using
|
||||
`mnesia:create_schema/2`
|
||||
|
||||
```erlang
|
||||
Erlang/OTP 22 [erts-10.7] ...
|
||||
|
||||
Eshell V10.7 (abort with ^G)
|
||||
1> mnesia:create_schema([node()],
|
||||
[{backend_types,[{rocksdb_copies,mnesia_rocksdb}]}]).
|
||||
ok
|
||||
2> mnesia:start().
|
||||
ok
|
||||
3> mnesia_schema:backend_types().
|
||||
[ram_copies,disc_copies,disc_only_copies,rocksdb_copies]
|
||||
```
|
||||
|
||||
(In `mnesia_rocksdb`, a shortcut for this exists in `mnesia_rocksdb:create_schema(Nodes)`.)
|
||||
|
||||
2. Add it when starting mnesia, using `mnesia:start/1` (undocumented)
|
||||
|
||||
```erlang
|
||||
Eshell V10.7 (abort with ^G)
|
||||
1> mnesia:create_schema([node()]).
|
||||
ok
|
||||
2> mnesia:start([{schema,[{backend_types,
|
||||
[{rocksdb_copies,mnesia_rocksdb}]}]}]).
|
||||
ok
|
||||
3> mnesia_schema:backend_types().
|
||||
[ram_copies,disc_copies,disc_only_copies]
|
||||
```
|
||||
|
||||
3. Call `mnesia_schema:add_backend_type/2` when mnesia is running.
|
||||
|
||||
```erlang
|
||||
Eshell V10.7 (abort with ^G)
|
||||
1> mnesia:create_schema([node()]).
|
||||
ok
|
||||
2> mnesia:start().
|
||||
ok
|
||||
3> mnesia_schema:add_backend_type(rocksdb_copies,mnesia_rocksdb).
|
||||
{atomic,ok}
|
||||
4> mnesia_schema:backend_types().
|
||||
[ram_copies,disc_copies,disc_only_copies,rocksdb_copies]
|
||||
```
|
||||
|
||||
In all cases the schema is updated, and other nodes, and subsequently
|
||||
added nodes, will automatically receive the information.
|
||||
The function `mnesia_schema:backend_types()` shows which backend plugin
|
||||
aliases are registered.
|
||||
|
||||
The information is also displayed when calling `mnesia:info()`:
|
||||
|
||||
```erlang
|
||||
5> mnesia:info().
|
||||
---> Processes holding locks <---
|
||||
---> Processes waiting for locks <---
|
||||
---> Participant transactions <---
|
||||
---> Coordinator transactions <---
|
||||
---> Uncertain transactions <---
|
||||
---> Active tables <---
|
||||
schema : with 1 records occupying 443 words of mem
|
||||
===> System info in version "4.16.3", debug level = none <===
|
||||
opt_disc. Directory "/.../Mnesia.nonode@nohost" is used.
|
||||
use fallback at restart = false
|
||||
running db nodes = [nonode@nohost]
|
||||
stopped db nodes = []
|
||||
master node tables = []
|
||||
backend types = rocksdb_copies - mnesia_rocksdb
|
||||
remote = []
|
||||
ram_copies = []
|
||||
disc_copies = [schema]
|
||||
disc_only_copies = []
|
||||
[{nonode@nohost,disc_copies}] = [schema]
|
||||
2 transactions committed, 0 aborted, 0 restarted, 0 logged to disc
|
||||
0 held locks, 0 in queue; 0 local transactions, 0 remote
|
||||
0 transactions waits for other nodes: []
|
||||
ok
|
||||
```
|
||||
|
||||
To illustrate how mnesia persists the information in the schema:
|
||||
|
||||
```erlang
|
||||
6> mnesia:table_info(schema,user_properties).
|
||||
[{mnesia_backend_types,[{rocksdb_copies,mnesia_rocksdb}]}]
|
||||
```
|
||||
|
||||
#### Rocksdb registration shortcut
|
||||
|
||||
Call `mnesia_rocksdb:register()` after starting mnesia.
|
||||
|
||||
#### Creating a table
|
||||
|
||||
Put `{rocksdb_copies, [node()]}` into the table definitions of
|
||||
tables you want to be in RocksDB.
|
||||
|
||||
```erlang
|
||||
4> mnesia:create_table(t, [{rocksdb_copies,[node()]}]).
|
||||
{atomic,ok}
|
||||
5> rr(mnesia).
|
||||
[commit,cstruct,cyclic,decision,log_header,mnesia_select,
|
||||
tid,tidstore]
|
||||
6> mnesia:table_info(t,cstruct).
|
||||
#cstruct{name = t,type = set,ram_copies = [],
|
||||
disc_copies = [],disc_only_copies = [],
|
||||
external_copies = [{{rocksdb_copies,mnesia_rocksdb},
|
||||
[nonode@nohost]}],
|
||||
load_order = 0,access_mode = read_write,majority = false,
|
||||
index = [],snmp = [],local_content = false,record_name = t,
|
||||
attributes = [key,val],
|
||||
user_properties = [],frag_properties = [],
|
||||
storage_properties = [],
|
||||
cookie = {{1621758137965715000,-576460752303423420,1},
|
||||
nonode@nohost},
|
||||
version = {{2,0},[]}}
|
||||
```
|
||||
|
||||
In the example above, we take a peek at the `cstruct`, which is the
|
||||
internal metadata structure for mnesia tables. The attribute showing
|
||||
that the table has been created with a `rocksdb_copies` instance, is
|
||||
the `external_copies` attribute. It lists the alias, the callback module
|
||||
and the nodes, where the instances reside.
|
||||
|
||||
The table works essentially like one of the built-in table types.
|
||||
If we want to find out which type, we can query the callback module:
|
||||
|
||||
```erlang
|
||||
8> mnesia_rocksdb:semantics(rocksdb_copies, storage).
|
||||
disc_only_copies
|
||||
```
|
||||
|
||||
Consult the `mnesia_rocksdb` man page for more info on the
|
||||
`Mod:semantics/2` function.
|
||||
|
||||
### New indexing functionality
|
||||
|
||||
With the introduction of backend plugins, a few improvements were made
|
||||
to mnesia's indexing support.
|
||||
|
||||
#### Persistent indexes
|
||||
|
||||
In the past, and still with the built-in types, indexes were always
|
||||
rebuilt on startup. Since backend plugins were introduced mainly in
|
||||
order to support very large tables, a couple of callback functions
|
||||
were added in order to detect whether a full rebuild is needed.
|
||||
|
||||
> The callback functions are `Mod:is_index_consistent/2` and
|
||||
> `Mod:index_is_consistent/3`.
|
||||
> The first function (figuratively) always returns `false` for indexes
|
||||
> on built-in table types. Backend plugin modules should always return
|
||||
> `false` if they have no information. After building the index, mnesia
|
||||
> calls `Mod:index_is_consistent(Alias, IxTab, true)`, and the callback
|
||||
> is expected to persist this information. `IxTab`, in this case, is
|
||||
> a logical name for the index 'table': `{Tab, index, PosInfo}`
|
||||
|
||||
#### Ordered indexes
|
||||
|
||||
A problem in the past with mnesia indexing has been that indexes with
|
||||
very large fan-out were inefficient. Indexes were represented as `bag`
|
||||
tables, and the cost of inserting a secondary key was proportional to
|
||||
the number of identical secondary keys already in the index.
|
||||
|
||||
When adding the backend plugin support - also not least because the
|
||||
first candidate LevelDb didn't do bags well - support for ordered
|
||||
indexes was added. They turn out to be have much more stable performance
|
||||
for indexes with large fan-out. They also work on all built-in table
|
||||
types.
|
||||
|
||||
When creating an index, you can specify the type of index as `bag` or
|
||||
`ordered`. If you omit the type, it will default to `bag` for built-in
|
||||
table types, and for external types, whatever is the first type in the
|
||||
list of supported index types returned by `Mod:semantics(Alias, index_types)`.
|
||||
|
||||
> For `mnesia_rocksdb`, only `ordered` is supported, but a bug in mnesia
|
||||
> makes it ignore this, and try to create a bag index anyway. The
|
||||
> `mnesia_rocksdb` plugin rejects this.
|
||||
> Note that while e.g. mnesia_rocksdb supports regular bag tables, they are not
|
||||
> efficiently implemented.
|
||||
|
||||
Mnesia currently doesn't allow specifying an index type in
|
||||
`mnesia:add_table_index/2`, so simply indicate the index position,
|
||||
and let the backend choose the default.
|
||||
|
||||
Having ordered indexes opens up for some new possibilities, but
|
||||
there are currently no functions in mnesia such as index_first, index_next
|
||||
etc., or performing a select in index order.
|
||||
|
||||
#### Index plugins
|
||||
|
||||
Index plugins are a great new feature, also almost entirely undocumented.
|
||||
|
||||
An index plugin is a registered indexing function, which can operate
|
||||
on the entire object, and shall return a list of secondary keys.
|
||||
When registering an index plugin, it is given an alias, a callback module,
|
||||
and an function name, not unlike backend plugins. The index plugin alias
|
||||
must be an atom wrapped inside a 1-tuple, i.e. `{atom()}`.
|
||||
|
||||
To illustrate, we use a sample indexing function implemented in
|
||||
mnesia_rocksdb, which checks all non-key attributes of an object,
|
||||
and for each value that is a list, makes each list element a secondary
|
||||
key value.
|
||||
|
||||
```erlang
|
||||
9> mnesia_schema:add_index_plugin({lv}, mnesia_rocksdb, ix_listvals).
|
||||
{atomic,ok}
|
||||
10> mnesia:add_table_index(t,{lv}).
|
||||
{atomic,ok}
|
||||
11> mnesia:dirty_write({t,1,[a,b]}).
|
||||
ok
|
||||
12> mnesia:dirty_write({t,2,[b,c]}).
|
||||
ok
|
||||
13> mnesia:dirty_index_read(t,a,{lv}).
|
||||
[{t,1,[a,b]}]
|
||||
14> mnesia:dirty_index_read(t,b,{lv}).
|
||||
[{t,1,[a,b]},{t,2,[b,c]}]
|
||||
15> mnesia:dirty_index_read(t,c,{lv}).
|
||||
[{t,2,[b,c]}]
|
||||
```
|
||||
|
||||
For clarity, this is the implementation of the index callback:
|
||||
|
||||
```erlang
|
||||
ix_listvals(_Tab, _Pos, Obj) ->
|
||||
lists:foldl(
|
||||
fun(V, Acc) when is_list(V) ->
|
||||
V ++ Acc;
|
||||
(_, Acc) ->
|
||||
Acc
|
||||
end, [], tl(tuple_to_list(Obj))).
|
||||
```
|
||||
|
||||
Note that the index callback must be a pure function, as it
|
||||
is also relied upon when deleting objects. That is, it must
|
||||
always return the same values when called with a specific
|
||||
set of input arguments.
|
||||
@@ -0,0 +1,55 @@
|
||||
/* standard EDoc style sheet */
|
||||
body {
|
||||
font-family: Verdana, Arial, Helvetica, sans-serif;
|
||||
margin-left: .25in;
|
||||
margin-right: .2in;
|
||||
margin-top: 0.2in;
|
||||
margin-bottom: 0.2in;
|
||||
color: #000000;
|
||||
background-color: #ffffff;
|
||||
}
|
||||
h1,h2 {
|
||||
margin-left: -0.2in;
|
||||
}
|
||||
div.navbar {
|
||||
background-color: #add8e6;
|
||||
padding: 0.2em;
|
||||
}
|
||||
h2.indextitle {
|
||||
padding: 0.4em;
|
||||
background-color: #add8e6;
|
||||
}
|
||||
h3.function,h3.typedecl {
|
||||
background-color: #add8e6;
|
||||
padding-left: 1em;
|
||||
}
|
||||
div.spec {
|
||||
margin-left: 2em;
|
||||
background-color: #eeeeee;
|
||||
}
|
||||
a.module {
|
||||
text-decoration:none
|
||||
}
|
||||
a.module:hover {
|
||||
background-color: #eeeeee;
|
||||
}
|
||||
ul.definitions {
|
||||
list-style-type: none;
|
||||
}
|
||||
ul.index {
|
||||
list-style-type: none;
|
||||
background-color: #eeeeee;
|
||||
}
|
||||
|
||||
/*
|
||||
* Minor style tweaks
|
||||
*/
|
||||
ul {
|
||||
list-style-type: square;
|
||||
}
|
||||
table {
|
||||
border-collapse: collapse;
|
||||
}
|
||||
td {
|
||||
padding: 3
|
||||
}
|
||||
Reference in New Issue
Block a user