Re: Slow Restoration of a template1 Database (ALTER GROUP)

Tom,

Is the "index bloat" prevented/reduced in newer versions of Postgres?

Is there a way to prevent/reduce it with the current version of Postgres I'm using?

Many Thanks,
Ben

"Ben Young" <Ben(dot)Young(at)etrials(dot)com> writes:
> template1=# VACUUM FULL VERBOSE pg_group;
> INFO: --Relation pg_catalog.pg_group--
> INFO: Pages 124: Changed 1, reaped 124, Empty 0, New 0; Tup 4: Vac 966, Keep/VTL 0/0, UnUsed 156, MinLen 92, MaxLen 136; Re-using: Free/Avail. Space 1008360/1008360; EndEmpty/Avail. Pages 0/124.
> CPU 0.01s/0.00u sec elapsed 0.07 sec.
> INFO: Index pg_group_name_index: Pages 19072; Tuples 4: Deleted 966.
^^^^^
> CPU 1.51s/0.25u sec elapsed 17.19 sec.
> INFO: Index pg_group_sysid_index: Pages 4313; Tuples 4: Deleted 966.
^^^^
> CPU 0.48s/0.04u sec elapsed 6.06 sec.

Whoa. Can you say "index bloat"?

I think that the only way to fix this is to REINDEX pg_group, which IIRC
in 7.3 requires stopping the postmaster and doing it in a standalone
backend (check the REINDEX reference page for details). Make sure the
toast table gets reindexed too, as its index is oversized as well.
(Recent PG versions will automatically reindex the toast table when you
reindex its parent table, but I forget whether 7.3 did so; you might
have to explicitly "reindex pg_toast.pg_toast_1261".)

regards, tom lane

"Ben Young" <Ben(dot)Young(at)etrials(dot)com> writes:
> Is the "index bloat" prevented/reduced in newer versions of Postgres?

Depends on what's causing it. Have you been inventing alphabetically
greater group names and getting rid of smaller names over time? If so,
this is a known problem that should be fixed in 7.4. The 7.4 release
notes say:

In previous releases, B-tree index pages that were left empty
because of deleted rows could only be reused by rows with index
values similar to the rows originally indexed on that page. In 7.4,
VACUUM records empty index pages and allows them to be reused for
any future index rows.

regards, tom lane