How to troubleshoot a dirty database

This document will take you through how to resolve a ‘dirty database’ error. During an upgrade, the pgsql, codeintel-db, and codeinsights-db databases must be migrated. If the upgrade was interrupted during the migration, this can result in a ‘dirty database’ error.

The error will look something like this:

ERROR: Failed to migrate the DB. Please contact [email protected] for further assistance: Dirty database version 1528395797. Fix and force version.

Resolving this error requires discovering which migration file failed to run, and manually attempting to run that migration.

Prerequisites

  • This document assumes that you are installing Sourcegraph or were attempting an upgrade when an error occurred.
  • NOTE: If you encountered this error during an upgrade, ensure you followed the proper step upgrade process documented here. If you skipped a minor version during an upgrade, you will need to revert back to the last minor version your instance was on before following the steps in this document.

The following procedure requires that you are able to execute commands from inside the database container. Learn more about shelling into kubernetes, docker-compose, and Sourcegraph single-container instances at these links.

TL;DR Steps to resolve

These steps pertain to the frontend database (pgsql) and are meant as a quick read for admins familiar with sql and database administration, for more explanation and details see the detailed steps to resolution below.

  1. Check the schema version in psql using the following query: SELECT * FROM schema_migrations;. If it’s dirty, note the migration’s version number.
  2. Find the up migration with that migration’s version number in https://github.com/sourcegraph/sourcegraph/tree/<YOUR-SOURCEGRAPH-VERSION>/migrations/frontend, making sure to go to <YOUR-SOURCEGRAPH-VERSION>
    • Note: migrations in this directory are specific to the pgsql frontend database, learn about other databases in the detailed steps to resolution
  3. Run the code there explicitly.
  4. Manually clear the dirty flag on the schema_migrations table.
  5. Start up again and the remaining migrations should succeed, otherwise repeat.

Detailed Steps to resolve

1. Identify incomplete migration

When migrations run, the schema_migrations table is updated to show the state of migrations. The dirty column, when set t (true), indicates a migration was attempted but did not complete successfully (either did not yet complete or failed to complete), and the version column indicates the version of the migration the database is on (when not dirty), or attempted to migrate to (when dirty). On startup, the frontend will not start if the schema_migrations dirty column is set to t.

Check schema version, by querying the database version table: SELECT * FROM schema_migrations; If it’s dirty, then note the version number for use in step 2.

Example:

SELECT * FROM schema_migrations;
version | dirty
------------+-------
1528395539 | t
(1 row)

This indicates that migration 1528395539 was running, but has not yet completed.

Note: for codeintel the schema version table is called codeintel_schema_migrations and for codeinsights its called codeinsights_schema_migrations

2. Run the sql queries to finish incomplete migrations

Sourcegraph’s migration files take for form of sql files following the snake case naming schema <version>_<description>.<up or down>.sql and can be found here in subdirectories for the specific database. Note frontend is the pgsql database.

  1. Find the up migration starting with the migration’s version number identified in step 1: https://github.com/sourcegraph/sourcegraph/tree/<YOUR-SOURCEGRAPH-VERSION>/migrations, making sure to go to <YOUR-SOURCEGRAPH-VERSION>

  2. Run the code from the identified migration up file explicitly using the psql CLI:

    • It’s possible that one or more commands from the migration ran successfully already. In these cases you may need to run the sql transaction in pieces. For example if a migration file creates multiple indexes and one index already exists you’ll need to manually run this transaction skipping that line or adding IF NOT EXISTS to the transaction.
    • If you’re running into unique index creation errors because of duplicate values please let us know at [email protected] or via your enterprise support channel.
    • There may be other error cases that don’t have an easy admin-only resolution, in these cases please let us know at [email protected] or via your enterprise support channel.

3. Verify database is clean and declare dirty=false

  1. Ensure the migration applied, and manually clear the dirty flag on the schema_migrations table.

    • example psql query: UPDATE schema_migrations SET version=1528395918, dirty=false;
    • Do not mark the migration table as clean if you have not verified that the migration was successfully completed.
    • Checking to see if a migration ran successfully requires looking at the migration’s sql file, and verifying that sql queries contained in the migration file have been applied to tables in the database.
    • Note: Many migrations do nothing but create tables and/or indexes or alter them.
    • You can get a description of a table and its associated indexes quickly using the \d <table name> psql shell command (note lack of semicolon). Using this information, you can determine whether a table exists, what columns it contains, and what indexes on it exist. Use this information to determine if commands in a migration ran successfully before setting dirty=false.
  2. Start Sourcegraph again and the remaining migrations should succeed, otherwise repeat this procedure again starting from the Identify incomplete migration step.

Additional Information

CREATE_INDEX_CONCURRENTLY

Some migrations utilize the CREATE INDEX CONCURRENTLY migration option which runs a query to create a table index as a background process (learn more here). If one of these migrations fails to complete, the database will register that a table index has been created, however the index will be unusable. If you use \d <table name> you will see the index for the table, but there will be nothing to tell you the indexing operation has failed. This database state can lead to poor search query performance, with searches attempting to utilize the incomplete table index.

To resolve this, you will then need to run the migration that creates the relevant index again, replacing CREATE INDEX CONCURRENTLY with REINDEX CONCURRENTLY. You can also drop and recreate the index.

To discover if such a damaged index exists by run the following query:

SELECT
    current_database() AS datname,
    pc.relname AS relname,
    1 AS count
FROM pg_class pc
JOIN pg_index pi ON pi.indexrelid = pc.oid
WHERE
    NOT indisvalid AND
    NOT EXISTS (SELECT 1 FROM pg_stat_progress_create_index pci WHERE pci.index_relid = pi.indexrelid)

Additionally Grafana will alert you of an index is in this state. The Grafana alert can be found under it’s database’s charts. Ex: Site Admin > Monitoring > Postgres > Invalid Indexes (unusable by query planner)

Further resources