I am worried that my restored database is very different from the original:
#check size of postgres databasepostgres@db1:/tmp$ psql -c "select pg_size_pretty(pg_database_size('test_db'));" pg_size_pretty---------------- 2105 MB(1 row)#backup databasepostgres@db1:/tmp$ pg_dump -Fc test_db > test_db_Fc.dump#rename postgres database (i.e. park it nearby)postgres@db1:/tmp$ psql -c "alter database test_db rename to test_db_20130322;"ALTER DATABASE-------(1 row)#restore test_dbpostgres@db1:/tmp$ pg_restore -Fc -C -d postgres test_db_Fc.dump#check size of restored postgres databasepostgres@db1:/tmp$ psql -c "select pg_size_pretty(pg_database_size('test_db'));" pg_size_pretty---------------- 257 MB(1 row)The original db is many times larger than the restored one. What is going on here?As far as I can tell, the website that test_db serves is still working perfectly well, after a restore, but I need to know what's up before i use a backup in live context.
FYI if I run vacuumdb on each database there seems to be no change in database size.
[Addendum, added later]In the tradition of RTFM I have gone hunting in the manual for PostgreSQL.Here are some more pieces to the puzzle
#is the autovacuum switched on?postgres@db1:/tmp$ psql -c "SHOW autovacuum;" autovacuum------------ on(1 row)#The "track counts" parameter is needed by autovacuum which uses statistics from database activity to know where to do its jobpostgres@db1:/tmp$ psql -c "SHOW track_counts;" track_counts-------------- on(1 row)#is there an autovacuum daemon resident in memory?postgres@db1:/tmp$ ps -ef | grep 'autovacuum'postgres 1261 1021 0 Jan23 ? 00:08:27 postgres: autovacuum launcher process postgres 18347 18149 0 00:33 pts/0 00:00:00 grep autovacuum#what's been happening on the live server?postgres@LIVEdb1:/tmp$ psql -c "SELECT relname, last_vacuum, last_autovacuum, last_analyze, last_autoanalyze from pg_stat_all_tables;"#result is list of 65 tables (out about 300), all empty (no dates at all)Gratefully following up on @craig-ringer's advice to look into VACUUM FULL I turned to PostgreSQL documentation, (paraphrased) "... In the worst case where your disk is nearly full, VACUUM FULL may be the only workable alternative. ... (but) the usual goal of routine vacuuming is to avoid needing VACUUM FULL. The autovacuum daemon attempts to do standard VACUUMs often enough to maintain steady-state usage of disk space ..."
I will follow @chris-travers advice and map out the number of rows in tables from each version of the database. I think in my case it'd be fair to say that VACUUM FULL will relieve the pressure on disk space, and it'll make original_vs_restored look better but there's still this red flag of excessive bloat. I think autovacuum isn't doing anything and that's a worry! Thanks for the guidance so far, it's fascinating.
