As all of you know after upgrading the database server from one version to other major version, ANALYZE command should be executed to update the pg_catalogs on newly populated data. On a huge upgraded database, its a challenge for the application to gain its performance back without updating the statistics. In PostgreSQL 9.4, an option “vacuumdb –analyze-in-stages”
will make this work faster to produce usable statistics required by the optimizer. It runs in three stages with different configuration settings(default_statistics_target/vacuum_cost_delay) to analyze the database.
If the database followed any of the up-gradation procedure like pg_dump/pg_restore or pg_upgrade, then its recommended to use “vacuumdb –analyze-in-stages”
bash-4.1$ /usr/local/pgpatch/pg/bin/vacuumdb -p 9999 --analyze-in-stages -d tester
Generating minimal optimizer statistics (1 target)
Generating medium optimizer statistics (10 targets)
Generating default (full) optimizer statistics