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<ol class="chapter"><li class="chapter-item expanded affix "><li class="part-title">Introduction</li><li class="chapter-item expanded "><a href="../welcome_and_overview.html">Welcome and Overview</a></li><li class="chapter-item expanded affix "><li class="part-title">Setup</li><li class="chapter-item expanded "><a href="../setup/installation.html">Installation</a></li><li class="chapter-item expanded "><a href="../postgres.html">Using Postgres</a></li><li class="chapter-item expanded "><a href="../reverse_proxy.html">Configuring a Reverse Proxy</a></li><li class="chapter-item expanded "><a href="../setup/forward_proxy.html">Configuring a Forward/Outbound Proxy</a></li><li class="chapter-item expanded "><a href="../turn-howto.html">Configuring a Turn Server</a></li><li class="chapter-item expanded "><a href="../delegate.html">Delegation</a></li><li class="chapter-item expanded affix "><li class="part-title">Upgrading</li><li class="chapter-item expanded "><a href="../upgrade.html">Upgrading between Synapse Versions</a></li><li class="chapter-item expanded affix "><li class="part-title">Usage</li><li class="chapter-item expanded "><a href="../federate.html">Federation</a></li><li class="chapter-item expanded "><a href="../usage/configuration/index.html">Configuration</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../usage/configuration/config_documentation.html">Configuration Manual</a></li><li class="chapter-item expanded "><a href="../usage/configuration/homeserver_sample_config.html">Homeserver Sample Config File</a></li><li class="chapter-item expanded "><a href="../usage/configuration/logging_sample_config.html">Logging Sample Config File</a></li><li class="chapter-item expanded "><a href="../structured_logging.html">Structured Logging</a></li><li class="chapter-item expanded "><a href="../templates.html">Templates</a></li><li class="chapter-item expanded "><a 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href="../modules/spam_checker_callbacks.html">Spam checker callbacks</a></li><li class="chapter-item expanded "><a href="../modules/third_party_rules_callbacks.html">Third-party rules callbacks</a></li><li class="chapter-item expanded "><a href="../modules/presence_router_callbacks.html">Presence router callbacks</a></li><li class="chapter-item expanded "><a href="../modules/account_validity_callbacks.html">Account validity callbacks</a></li><li class="chapter-item expanded "><a href="../modules/password_auth_provider_callbacks.html">Password auth provider callbacks</a></li><li class="chapter-item expanded "><a href="../modules/background_update_controller_callbacks.html">Background update controller callbacks</a></li><li class="chapter-item expanded "><a href="../modules/account_data_callbacks.html">Account data callbacks</a></li><li class="chapter-item expanded "><a href="../modules/porting_legacy_module.html">Porting a legacy module to the new interface</a></li></ol></li></ol></li><li class="chapter-item expanded "><a href="../workers.html">Workers</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../synctl_workers.html">Using synctl with Workers</a></li><li class="chapter-item expanded "><a href="../systemd-with-workers/index.html">Systemd</a></li></ol></li></ol></li><li class="chapter-item expanded "><a href="../usage/administration/index.html">Administration</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../usage/administration/admin_api/index.html">Admin API</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../admin_api/account_validity.html">Account Validity</a></li><li class="chapter-item expanded "><a href="../usage/administration/admin_api/background_updates.html">Background Updates</a></li><li class="chapter-item expanded "><a href="../admin_api/event_reports.html">Event Reports</a></li><li class="chapter-item expanded "><a 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and User Statistics</a></li></ol></li><li class="chapter-item expanded "><div>Scripts</div></li><li class="chapter-item expanded affix "><li class="part-title">Other</li><li class="chapter-item expanded "><a href="../deprecation_policy.html">Dependency Deprecation Policy</a></li><li class="chapter-item expanded "><a href="../other/running_synapse_on_single_board_computers.html">Running Synapse on a Single-Board Computer</a></li></ol>
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<h1 id="synapse-database-schema-files"><a class="header" href="#synapse-database-schema-files">Synapse database schema files</a></h1>
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<p>Synapse's database schema is stored in the <code>synapse.storage.schema</code> module.</p>
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<h2 id="logical-databases"><a class="header" href="#logical-databases">Logical databases</a></h2>
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<p>Synapse supports splitting its datastore across multiple physical databases (which can
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be useful for large installations), and the schema files are therefore split according
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to the logical database they apply to.</p>
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<p>At the time of writing, the following "logical" databases are supported:</p>
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<ul>
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<li><code>state</code> - used to store Matrix room state (more specifically, <code>state_groups</code>,
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their relationships and contents).</li>
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<li><code>main</code> - stores everything else.</li>
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</ul>
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<p>Additionally, the <code>common</code> directory contains schema files for tables which must be
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present on <em>all</em> physical databases.</p>
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<h2 id="synapse-schema-versions"><a class="header" href="#synapse-schema-versions">Synapse schema versions</a></h2>
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<p>Synapse manages its database schema via "schema versions". These are mainly used to
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help avoid confusion if the Synapse codebase is rolled back after the database is
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updated. They work as follows:</p>
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<ul>
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<li>
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<p>The Synapse codebase defines a constant <code>synapse.storage.schema.SCHEMA_VERSION</code>
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which represents the expectations made about the database by that version. For
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example, as of Synapse v1.36, this is <code>59</code>.</p>
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</li>
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<li>
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<p>The database stores a "compatibility version" in
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<code>schema_compat_version.compat_version</code> which defines the <code>SCHEMA_VERSION</code> of the
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oldest version of Synapse which will work with the database. On startup, if
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<code>compat_version</code> is found to be newer than <code>SCHEMA_VERSION</code>, Synapse will refuse to
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start.</p>
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<p>Synapse automatically updates this field from
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<code>synapse.storage.schema.SCHEMA_COMPAT_VERSION</code>.</p>
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</li>
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<li>
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<p>Whenever a backwards-incompatible change is made to the database format (normally
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via a <code>delta</code> file), <code>synapse.storage.schema.SCHEMA_COMPAT_VERSION</code> is also updated
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so that administrators can not accidentally roll back to a too-old version of Synapse.</p>
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</li>
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</ul>
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<p>Generally, the goal is to maintain compatibility with at least one or two previous
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releases of Synapse, so any substantial change tends to require multiple releases and a
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bit of forward-planning to get right.</p>
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<p>As a worked example: we want to remove the <code>room_stats_historical</code> table. Here is how it
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might pan out.</p>
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<ol>
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<li>
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<p>Replace any code that <em>reads</em> from <code>room_stats_historical</code> with alternative
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implementations, but keep writing to it in case of rollback to an earlier version.
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Also, increase <code>synapse.storage.schema.SCHEMA_VERSION</code>. In this
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instance, there is no existing code which reads from <code>room_stats_historical</code>, so
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our starting point is:</p>
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<p>v1.36.0: <code>SCHEMA_VERSION=59</code>, <code>SCHEMA_COMPAT_VERSION=59</code></p>
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</li>
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<li>
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<p>Next (say in Synapse v1.37.0): remove the code that <em>writes</em> to
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<code>room_stats_historical</code>, but don’t yet remove the table in case of rollback to
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v1.36.0. Again, we increase <code>synapse.storage.schema.SCHEMA_VERSION</code>, but
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because we have not broken compatibility with v1.36, we do not yet update
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<code>SCHEMA_COMPAT_VERSION</code>. We now have:</p>
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<p>v1.37.0: <code>SCHEMA_VERSION=60</code>, <code>SCHEMA_COMPAT_VERSION=59</code>.</p>
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</li>
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<li>
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<p>Later (say in Synapse v1.38.0): we can remove the table altogether. This will
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break compatibility with v1.36.0, so we must update <code>SCHEMA_COMPAT_VERSION</code> accordingly.
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There is no need to update <code>synapse.storage.schema.SCHEMA_VERSION</code>, since there is no
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change to the Synapse codebase here. So we end up with:</p>
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<p>v1.38.0: <code>SCHEMA_VERSION=60</code>, <code>SCHEMA_COMPAT_VERSION=60</code>.</p>
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</li>
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</ol>
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<p>If in doubt about whether to update <code>SCHEMA_VERSION</code> or not, it is generally best to
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lean towards doing so.</p>
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<h2 id="full-schema-dumps"><a class="header" href="#full-schema-dumps">Full schema dumps</a></h2>
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<p>In the <code>full_schemas</code> directories, only the most recently-numbered snapshot is used
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(<code>54</code> at the time of writing). Older snapshots (eg, <code>16</code>) are present for historical
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reference only.</p>
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<h3 id="building-full-schema-dumps"><a class="header" href="#building-full-schema-dumps">Building full schema dumps</a></h3>
|
||
<p>If you want to recreate these schemas, they need to be made from a database that
|
||
has had all background updates run.</p>
|
||
<p>To do so, use <code>scripts-dev/make_full_schema.sh</code>. This will produce new
|
||
<code>full.sql.postgres</code> and <code>full.sql.sqlite</code> files.</p>
|
||
<p>Ensure postgres is installed, then run:</p>
|
||
<pre><code class="language-sh">./scripts-dev/make_full_schema.sh -p postgres_username -o output_dir/
|
||
</code></pre>
|
||
<p>NB at the time of writing, this script predates the split into separate <code>state</code>/<code>main</code>
|
||
databases so will require updates to handle that correctly.</p>
|
||
<h2 id="delta-files"><a class="header" href="#delta-files">Delta files</a></h2>
|
||
<p>Delta files define the steps required to upgrade the database from an earlier version.
|
||
They can be written as either a file containing a series of SQL statements, or a Python
|
||
module.</p>
|
||
<p>Synapse remembers which delta files it has applied to a database (they are stored in the
|
||
<code>applied_schema_deltas</code> table) and will not re-apply them (even if a given file is
|
||
subsequently updated).</p>
|
||
<p>Delta files should be placed in a directory named <code>synapse/storage/schema/<database>/delta/<version>/</code>.
|
||
They are applied in alphanumeric order, so by convention the first two characters
|
||
of the filename should be an integer such as <code>01</code>, to put the file in the right order.</p>
|
||
<h3 id="sql-delta-files"><a class="header" href="#sql-delta-files">SQL delta files</a></h3>
|
||
<p>These should be named <code>*.sql</code>, or — for changes which should only be applied for a
|
||
given database engine — <code>*.sql.posgres</code> or <code>*.sql.sqlite</code>. For example, a delta which
|
||
adds a new column to the <code>foo</code> table might be called <code>01add_bar_to_foo.sql</code>.</p>
|
||
<p>Note that our SQL parser is a bit simple - it understands comments (<code>--</code> and <code>/*...*/</code>),
|
||
but complex statements which require a <code>;</code> in the middle of them (such as <code>CREATE TRIGGER</code>) are beyond it and you'll have to use a Python delta file.</p>
|
||
<h3 id="python-delta-files"><a class="header" href="#python-delta-files">Python delta files</a></h3>
|
||
<p>For more flexibility, a delta file can take the form of a python module. These should
|
||
be named <code>*.py</code>. Note that database-engine-specific modules are not supported here –
|
||
instead you can write <code>if isinstance(database_engine, PostgresEngine)</code> or similar.</p>
|
||
<p>A Python delta module should define either or both of the following functions:</p>
|
||
<pre><code class="language-python">import synapse.config.homeserver
|
||
import synapse.storage.engines
|
||
import synapse.storage.types
|
||
|
||
|
||
def run_create(
|
||
cur: synapse.storage.types.Cursor,
|
||
database_engine: synapse.storage.engines.BaseDatabaseEngine,
|
||
) -> None:
|
||
"""Called whenever an existing or new database is to be upgraded"""
|
||
...
|
||
|
||
def run_upgrade(
|
||
cur: synapse.storage.types.Cursor,
|
||
database_engine: synapse.storage.engines.BaseDatabaseEngine,
|
||
config: synapse.config.homeserver.HomeServerConfig,
|
||
) -> None:
|
||
"""Called whenever an existing database is to be upgraded."""
|
||
...
|
||
</code></pre>
|
||
<h2 id="boolean-columns"><a class="header" href="#boolean-columns">Boolean columns</a></h2>
|
||
<p>Boolean columns require special treatment, since SQLite treats booleans the
|
||
same as integers.</p>
|
||
<p>There are three separate aspects to this:</p>
|
||
<ul>
|
||
<li>
|
||
<p>Any new boolean column must be added to the <code>BOOLEAN_COLUMNS</code> list in
|
||
<code>synapse/_scripts/synapse_port_db.py</code>. This tells the port script to cast
|
||
the integer value from SQLite to a boolean before writing the value to the
|
||
postgres database.</p>
|
||
</li>
|
||
<li>
|
||
<p>Before SQLite 3.23, <code>TRUE</code> and <code>FALSE</code> were not recognised as constants by
|
||
SQLite, and the <code>IS [NOT] TRUE</code>/<code>IS [NOT] FALSE</code> operators were not
|
||
supported. This makes it necessary to avoid using <code>TRUE</code> and <code>FALSE</code>
|
||
constants in SQL commands.</p>
|
||
<p>For example, to insert a <code>TRUE</code> value into the database, write:</p>
|
||
<pre><code class="language-python">txn.execute("INSERT INTO tbl(col) VALUES (?)", (True, ))
|
||
</code></pre>
|
||
</li>
|
||
<li>
|
||
<p>Default values for new boolean columns present a particular
|
||
difficulty. Generally it is best to create separate schema files for
|
||
Postgres and SQLite. For example:</p>
|
||
<pre><code class="language-sql"># in 00delta.sql.postgres:
|
||
ALTER TABLE tbl ADD COLUMN col BOOLEAN DEFAULT FALSE;
|
||
</code></pre>
|
||
<pre><code class="language-sql"># in 00delta.sql.sqlite:
|
||
ALTER TABLE tbl ADD COLUMN col BOOLEAN DEFAULT 0;
|
||
</code></pre>
|
||
<p>Note that there is a particularly insidious failure mode here: the Postgres
|
||
flavour will be accepted by SQLite 3.22, but will give a column whose
|
||
default value is the <strong>string</strong> <code>"FALSE"</code> - which, when cast back to a boolean
|
||
in Python, evaluates to <code>True</code>.</p>
|
||
</li>
|
||
</ul>
|
||
<h2 id="event_id-global-uniqueness"><a class="header" href="#event_id-global-uniqueness"><code>event_id</code> global uniqueness</a></h2>
|
||
<p>In room versions <code>1</code> and <code>2</code> it's possible to end up with two events with the
|
||
same <code>event_id</code> (in the same or different rooms). After room version <code>3</code>, that
|
||
can only happen with a hash collision, which we basically hope will never
|
||
happen.</p>
|
||
<p>There are several places in Synapse and even Matrix APIs like <a href="https://spec.matrix.org/v1.1/server-server-api/#get_matrixfederationv1eventeventid"><code>GET /_matrix/federation/v1/event/{eventId}</code></a>
|
||
where we assume that event IDs are globally unique.</p>
|
||
<p>But hash collisions are still possible, and by treating event IDs as room
|
||
scoped, we can reduce the possibility of a hash collision. When scoping
|
||
<code>event_id</code> in the database schema, it should be also accompanied by <code>room_id</code>
|
||
(<code>PRIMARY KEY (room_id, event_id)</code>) and lookups should be done through the pair
|
||
<code>(room_id, event_id)</code>.</p>
|
||
<p>There has been a lot of debate on this in places like
|
||
https://github.com/matrix-org/matrix-spec-proposals/issues/2779 and
|
||
<a href="https://github.com/matrix-org/matrix-spec-proposals/pull/2848">MSC2848</a> which
|
||
has no resolution yet (as of 2022-09-01).</p>
|
||
|
||
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