Gerrit Postgres based persistent cache

Gerrit lib module to swap existing persistent cache implementation (that is H2 based) with implementation that stores data in Postgres. Note that is uses INSERT INTO ... ON CONFLICT DO UPDATE ... upsert syntax therefore it is Postgres 9.5+ compatible.

How to build

Build this module similarly to standalone build for any other, bazel based Gerrit plugin:

• Clone the cache-postgres source tree
• Run bazel build cache-postgres
• The cache-postgres.jar module is generated under /bazel-genfiles/cache-postgres.jar

How install

Copy cache-postgres.jar library to Gerrit /lib and add the following two extra settings to gerrit.config:

[gerrit]
  installModule = com.googlesource.gerrit.modules.cache.pg.CacheModule

[cache]
  url = jdbc:postgresql://localhost:5432/gerrit_caches?user=gerrit&password=gerrit

Core Gerrit settings: section cache

cache.url : URI that specifies connection to existing DB (including both username and passwword).

cache.poolLimit : Maximum number of open database connections. If the server needs more than this number, request processing threads will wait up to cache.poolMaxWait seconds for a connection to be released before they abort with an exception. Default value is taken from database.poolLimit.

cache.poolMinIdle : Minimum number of connections to keep idle in the pool. Default is 4.

cache.poolMaxIdle : Maximum number of connections to keep idle in the pool. If there are more idle connections, connections will be closed instead of being returned back to the pool. Default is min(cache.poolLimit, 16).

cache.poolMaxWait Maximum amount of time a request processing thread will wait to acquire a database connection from the pool. If no connection is released within this time period, the processing thread will abort its current operations and return an error to the client. Values should use common unit suffixes to express their setting:

• ms, milliseconds
• s, sec, second, seconds
• m, min, minute, minutes
• h, hr, hour, hours

If a unit suffix is not specified, milliseconds is assumed. Default is 30 seconds.

Testing with docker based Postgres setup

One can start test Postgres server that contains both gerrit_review (Gerrit db) and gerrit_caches (db for caches) with the following command

docker-compose -f docker/gerrit-caches-compose.yaml up

One nedds to add the following parameters to gerrit.config

git config --file ${GERRIT_ETC_DIR}/gerrit.config database.type POSTGRESQL
git config --file ${GERRIT_ETC_DIR}/gerrit.config database.hostname localhost
git config --file ${GERRIT_ETC_DIR}/gerrit.config database.port 5432
git config --file ${GERRIT_ETC_DIR}/gerrit.config database.database gerrit_review
git config --file ${GERRIT_ETC_DIR}/gerrit.config database.username gerrit
git config --file ${GERRIT_ETC_DIR}/gerrit.config database.password gerrit
git config --file ${GERRIT_ETC_DIR}/gerrit.config cache.url "jdbc:postgresql://localhost:5432/gerrit_caches?user=gerrit&password=gerrit"

where GERRIT_ETC_DIR is GERRIT_SITE/etc;

Notes

• container name is gerrit-pg
• container uses docker_gerrit-db-data volume therefore restarting it preserves data
• details of Postgres user/dbs setup can be found in docker/create-gerrit-dbs.sh
• Postgres container details (ports, volumes, etc.) are in docker/gerrit-caches-compose.yaml