This is a document for PGroonga 2.X. See PGroonga 1.x document when you're using old PGroonga.
Normally PGroonga's WAL doesn't t apply on a standby database. If we use PGroonga with streaming replication.
Therefore, for example, a first "SELECT" on a primary database may become slower after we switch from a standby database. Because it takes time to apply PGroonga's WAL to the primary database.
In addition, we need to remove internal unused Groonga tables, columns and records periodically from the standby database with the
pgroonga_vacuum() function. Because
VACUUM isn't run on the standby database.
In the former case, we can apply PGroonga's WAL into the standby database automatically with the
pgroonga_wal_applier module. However, in the latter case, we can't execute automatically the
pgroonga_vacuum() funtion into the standby database.
We must configure the following parameters to use
shared_preload_libraries = 'pgroonga_standby_maintainer'