Update postgres docs (#9989)
Richard van der Hoff
GitHub
parent
6482075c95
commit
6660912226
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@ -1 +1 @@
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Fix outdated minimum PostgreSQL version in postgres.md.
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Updates to the PostgreSQL documentation (`postgres.md`).
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@ -0,0 +1 @@
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Updates to the PostgreSQL documentation (`postgres.md`).
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198
docs/postgres.md
198
docs/postgres.md
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@ -33,28 +33,15 @@ Assuming your PostgreSQL database user is called `postgres`, first authenticate
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# Or, if your system uses sudo to get administrative rights
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sudo -u postgres bash
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Then, create a user ``synapse_user`` with:
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Then, create a postgres user and a database with:
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# this will prompt for a password for the new user
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createuser --pwprompt synapse_user
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Before you can authenticate with the `synapse_user`, you must create a
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database that it can access. To create a database, first connect to the
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database with your database user:
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createdb --encoding=UTF8 --locale=C --template=template0 --owner=synapse_user synapse
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su - postgres # Or: sudo -u postgres bash
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psql
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and then run:
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CREATE DATABASE synapse
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ENCODING 'UTF8'
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LC_COLLATE='C'
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LC_CTYPE='C'
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template=template0
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OWNER synapse_user;
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This would create an appropriate database named `synapse` owned by the
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`synapse_user` user (which must already have been created as above).
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The above will create a user called `synapse_user`, and a database called
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`synapse`.
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Note that the PostgreSQL database *must* have the correct encoding set
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(as shown above), otherwise it will not be able to store UTF8 strings.
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@ -63,79 +50,6 @@ You may need to enable password authentication so `synapse_user` can
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connect to the database. See
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<https://www.postgresql.org/docs/current/auth-pg-hba-conf.html>.
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If you get an error along the lines of `FATAL: Ident authentication failed for
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user "synapse_user"`, you may need to use an authentication method other than
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`ident`:
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* If the `synapse_user` user has a password, add the password to the `database:`
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section of `homeserver.yaml`. Then add the following to `pg_hba.conf`:
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```
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host synapse synapse_user ::1/128 md5 # or `scram-sha-256` instead of `md5` if you use that
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```
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* If the `synapse_user` user does not have a password, then a password doesn't
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have to be added to `homeserver.yaml`. But the following does need to be added
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to `pg_hba.conf`:
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```
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host synapse synapse_user ::1/128 trust
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```
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Note that line order matters in `pg_hba.conf`, so make sure that if you do add a
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new line, it is inserted before:
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```
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host all all ::1/128 ident
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```
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### Fixing incorrect `COLLATE` or `CTYPE`
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Synapse will refuse to set up a new database if it has the wrong values of
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`COLLATE` and `CTYPE` set, and will log warnings on existing databases. Using
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different locales can cause issues if the locale library is updated from
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underneath the database, or if a different version of the locale is used on any
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replicas.
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The safest way to fix the issue is to take a dump and recreate the database with
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the correct `COLLATE` and `CTYPE` parameters (as shown above). It is also possible to change the
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parameters on a live database and run a `REINDEX` on the entire database,
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however extreme care must be taken to avoid database corruption.
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Note that the above may fail with an error about duplicate rows if corruption
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has already occurred, and such duplicate rows will need to be manually removed.
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## Fixing inconsistent sequences error
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Synapse uses Postgres sequences to generate IDs for various tables. A sequence
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and associated table can get out of sync if, for example, Synapse has been
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downgraded and then upgraded again.
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To fix the issue shut down Synapse (including any and all workers) and run the
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SQL command included in the error message. Once done Synapse should start
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successfully.
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## Tuning Postgres
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The default settings should be fine for most deployments. For larger
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scale deployments tuning some of the settings is recommended, details of
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which can be found at
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<https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server>.
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In particular, we've found tuning the following values helpful for
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performance:
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- `shared_buffers`
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- `effective_cache_size`
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- `work_mem`
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- `maintenance_work_mem`
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- `autovacuum_work_mem`
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Note that the appropriate values for those fields depend on the amount
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of free memory the database host has available.
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## Synapse config
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When you are ready to start using PostgreSQL, edit the `database`
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@ -165,18 +79,42 @@ may block for an extended period while it waits for a response from the
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database server. Example values might be:
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```yaml
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# seconds of inactivity after which TCP should send a keepalive message to the server
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keepalives_idle: 10
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database:
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args:
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# ... as above
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# the number of seconds after which a TCP keepalive message that is not
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# acknowledged by the server should be retransmitted
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keepalives_interval: 10
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# seconds of inactivity after which TCP should send a keepalive message to the server
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keepalives_idle: 10
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# the number of TCP keepalives that can be lost before the client's connection
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# to the server is considered dead
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keepalives_count: 3
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# the number of seconds after which a TCP keepalive message that is not
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# acknowledged by the server should be retransmitted
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keepalives_interval: 10
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# the number of TCP keepalives that can be lost before the client's connection
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# to the server is considered dead
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keepalives_count: 3
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```
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## Tuning Postgres
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The default settings should be fine for most deployments. For larger
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scale deployments tuning some of the settings is recommended, details of
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which can be found at
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<https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server>.
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In particular, we've found tuning the following values helpful for
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performance:
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- `shared_buffers`
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- `effective_cache_size`
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- `work_mem`
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- `maintenance_work_mem`
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- `autovacuum_work_mem`
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Note that the appropriate values for those fields depend on the amount
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of free memory the database host has available.
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## Porting from SQLite
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### Overview
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@ -185,9 +123,8 @@ The script `synapse_port_db` allows porting an existing synapse server
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backed by SQLite to using PostgreSQL. This is done in as a two phase
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process:
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1. Copy the existing SQLite database to a separate location (while the
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server is down) and running the port script against that offline
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database.
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1. Copy the existing SQLite database to a separate location and run
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the port script against that offline database.
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2. Shut down the server. Rerun the port script to port any data that
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has come in since taking the first snapshot. Restart server against
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the PostgreSQL database.
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@ -245,3 +182,60 @@ PostgreSQL database configuration file `homeserver-postgres.yaml`:
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./synctl start
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Synapse should now be running against PostgreSQL.
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## Troubleshooting
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### Alternative auth methods
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If you get an error along the lines of `FATAL: Ident authentication failed for
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user "synapse_user"`, you may need to use an authentication method other than
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`ident`:
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* If the `synapse_user` user has a password, add the password to the `database:`
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section of `homeserver.yaml`. Then add the following to `pg_hba.conf`:
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```
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host synapse synapse_user ::1/128 md5 # or `scram-sha-256` instead of `md5` if you use that
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```
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* If the `synapse_user` user does not have a password, then a password doesn't
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have to be added to `homeserver.yaml`. But the following does need to be added
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to `pg_hba.conf`:
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```
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host synapse synapse_user ::1/128 trust
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```
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Note that line order matters in `pg_hba.conf`, so make sure that if you do add a
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new line, it is inserted before:
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|
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```
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host all all ::1/128 ident
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```
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### Fixing incorrect `COLLATE` or `CTYPE`
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Synapse will refuse to set up a new database if it has the wrong values of
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`COLLATE` and `CTYPE` set, and will log warnings on existing databases. Using
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different locales can cause issues if the locale library is updated from
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underneath the database, or if a different version of the locale is used on any
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replicas.
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The safest way to fix the issue is to dump the database and recreate it with
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the correct locale parameter (as shown above). It is also possible to change the
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parameters on a live database and run a `REINDEX` on the entire database,
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however extreme care must be taken to avoid database corruption.
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Note that the above may fail with an error about duplicate rows if corruption
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has already occurred, and such duplicate rows will need to be manually removed.
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### Fixing inconsistent sequences error
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Synapse uses Postgres sequences to generate IDs for various tables. A sequence
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and associated table can get out of sync if, for example, Synapse has been
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downgraded and then upgraded again.
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To fix the issue shut down Synapse (including any and all workers) and run the
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SQL command included in the error message. Once done Synapse should start
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successfully.
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