debian-mirror-gitlab/doc/administration/troubleshooting/postgresql.md

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---
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stage: Enablement
group: Database
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
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type: reference
---
# PostgreSQL
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This page contains information about PostgreSQL the GitLab Support team uses
when troubleshooting. GitLab makes this information public, so that anyone can
make use of the Support team's collected knowledge.
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WARNING:
Some procedures documented here may break your GitLab instance. Use at your
own risk.
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If you're on a [paid tier](https://about.gitlab.com/pricing/) and aren't sure
how to use these commands, [contact Support](https://about.gitlab.com/support/)
for assistance with any issues you're having.
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## Other GitLab PostgreSQL documentation
This section is for links to information elsewhere in the GitLab documentation.
### Procedures
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- [Connect to the PostgreSQL console](https://docs.gitlab.com/omnibus/settings/database.html#connecting-to-the-bundled-postgresql-database).
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- [Omnibus database procedures](https://docs.gitlab.com/omnibus/settings/database.html) including:
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- SSL: enabling, disabling, and verifying.
- Enabling Write Ahead Log (WAL) archiving.
- Using an external (non-Omnibus) PostgreSQL installation; and backing it up.
- Listening on TCP/IP as well as or instead of sockets.
- Storing data in another location.
- Destructively reseeding the GitLab database.
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- Guidance around updating packaged PostgreSQL, including how to stop it
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from happening automatically.
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- [Information about external PostgreSQL](../postgresql/external.md).
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- [Running Geo with external PostgreSQL](../geo/setup/external_database.md).
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- [Upgrades when running PostgreSQL configured for HA](https://docs.gitlab.com/omnibus/settings/database.html#upgrading-a-gitlab-ha-cluster).
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- Consuming PostgreSQL from [within CI runners](../../ci/services/postgres.md).
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- [Using Slony to update PostgreSQL](../../update/upgrading_postgresql_using_slony.md).
- Uses replication to handle PostgreSQL upgrades if the schemas are the same.
- Reduces downtime to a short window for switching to the newer version.
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- Managing Omnibus PostgreSQL versions [from the development docs](https://docs.gitlab.com/omnibus/development/managing-postgresql-versions.html).
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- [PostgreSQL scaling](../postgresql/replication_and_failover.md)
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- Including [troubleshooting](../postgresql/replication_and_failover.md#troubleshooting)
`gitlab-ctl repmgr-check-master` (or `gitlab-ctl patroni check-leader` if
you're using Patroni) and PgBouncer errors.
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- [Developer database documentation](../../development/README.md#database-guides),
some of which is absolutely not for production use. Including:
- Understanding EXPLAIN plans.
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### Troubleshooting/Fixes
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- [GitLab database requirements](../../install/requirements.md#database),
including
- Support for MySQL was removed in GitLab 12.1; [migrate to PostgreSQL](../../update/mysql_to_postgresql.md).
- Required extension: `pg_trgm`
- Required extension: `btree_gist`
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- Errors like this in the `production/sidekiq` log; see:
[Set default_transaction_isolation into read committed](https://docs.gitlab.com/omnibus/settings/database.html#set-default_transaction_isolation-into-read-committed):
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```plaintext
ActiveRecord::StatementInvalid PG::TRSerializationFailure: ERROR: could not serialize access due to concurrent update
```
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- PostgreSQL HA [replication slot errors](https://docs.gitlab.com/omnibus/settings/database.html#troubleshooting-upgrades-in-an-ha-cluster):
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```plaintext
pg_basebackup: could not create temporary replication slot "pg_basebackup_12345": ERROR: all replication slots are in use
HINT: Free one or increase max_replication_slots.
```
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- Geo [replication errors](../geo/replication/troubleshooting.md#fixing-replication-errors) including:
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```plaintext
ERROR: replication slots can only be used if max_replication_slots > 0
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FATAL: could not start WAL streaming: ERROR: replication slot "geo_secondary_my_domain_com" does not exist
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Command exceeded allowed execution time
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PANIC: could not write to file 'pg_xlog/xlogtemp.123': No space left on device
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```
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- [Checking Geo configuration](../geo/replication/troubleshooting.md), including:
- Reconfiguring hosts/ports.
- Checking and fixing user/password mappings.
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- [Common Geo errors](../geo/replication/troubleshooting.md#fixing-common-errors).
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## Support topics
### Database deadlocks
References:
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- [Issue #1 Deadlocks with GitLab 12.1, PostgreSQL 10.7](https://gitlab.com/gitlab-org/gitlab/-/issues/30528).
- [Customer ticket (internal) GitLab 12.1.6](https://gitlab.zendesk.com/agent/tickets/134307)
and [Google doc (internal)](https://docs.google.com/document/d/19xw2d_D1ChLiU-MO1QzWab-4-QXgsIUcN5e_04WTKy4).
- [Issue #2 deadlocks can occur if an instance is flooded with pushes](https://gitlab.com/gitlab-org/gitlab/-/issues/33650).
Provided for context about how GitLab code can have this sort of
unanticipated effect in unusual situations.
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```plaintext
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ERROR: deadlock detected
```
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Three applicable timeouts are identified in the issue [#1](https://gitlab.com/gitlab-org/gitlab/-/issues/30528); our recommended settings are as follows:
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```ini
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deadlock_timeout = 5s
statement_timeout = 15s
idle_in_transaction_session_timeout = 60s
```
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Quoting from issue [#1](https://gitlab.com/gitlab-org/gitlab/-/issues/30528):
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> "If a deadlock is hit, and we resolve it through aborting the transaction after a short period, then the retry mechanisms we already have will make the deadlocked piece of work try again, and it's unlikely we'll deadlock multiple times in a row."
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NOTE:
In Support, our general approach to reconfiguring timeouts (applies also to the
HTTP stack) is that it's acceptable to do it temporarily as a workaround. If it
makes GitLab usable for the customer, then it buys time to understand the
problem more completely, implement a hot fix, or make some other change that
addresses the root cause. Generally, the timeouts should be put back to
reasonable defaults after the root cause is resolved.
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In this case, the guidance we had from development was to drop deadlock_timeout
or statement_timeout, but to leave the third setting at 60s. Setting
idle_in_transaction protects the database from sessions potentially hanging for
days. There's more discussion in [the issue relating to introducing this timeout on GitLab.com](https://gitlab.com/gitlab-com/gl-infra/production/-/issues/1053).
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PostgresSQL defaults:
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- `statement_timeout = 0` (never)
- `idle_in_transaction_session_timeout = 0` (never)
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Comments in issue [#1](https://gitlab.com/gitlab-org/gitlab/-/issues/30528)
indicate that these should both be set to at least a number of minutes for all
Omnibus GitLab installations (so they don't hang indefinitely). However, 15s
for statement_timeout is very short, and will only be effective if the
underlying infrastructure is very performant.
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See current settings with:
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```shell
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sudo gitlab-rails runner "c = ApplicationRecord.connection ; puts c.execute('SHOW statement_timeout').to_a ;
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puts c.execute('SHOW deadlock_timeout').to_a ;
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puts c.execute('SHOW idle_in_transaction_session_timeout').to_a ;"
```
It may take a little while to respond.
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```ruby
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{"statement_timeout"=>"1min"}
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{"deadlock_timeout"=>"0"}
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{"idle_in_transaction_session_timeout"=>"1min"}
```
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These settings can be updated in `/etc/gitlab/gitlab.rb` with:
```ruby
postgresql['deadlock_timeout'] = '5s'
postgresql['statement_timeout'] = '15s'
postgresql['idle_in_transaction_session_timeout'] = '60s'
```
Once saved, [reconfigure GitLab](../restart_gitlab.md#omnibus-gitlab-reconfigure) for the changes to take effect.
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NOTE:
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These are Omnibus GitLab settings. If an external database, such as a customer's PostgreSQL installation or Amazon RDS is being used, these values don't get set, and would have to be set externally.