Drop big index

Vojtech Rylko wrote:

I need to drop some b-tree indexes because they are not used anymore.
Size of indexes vary between 700 MB and 7 GB. I tried common DROP
INDEX... but this query performed so long and blocked table so I had to
interrupt it. Is there any way how to drop large indexes in non-blocking
or /faster/ way?

Unfortunately not (yet).
PostgreSQL 9.2 will have DROP INDEX CONCURRENTLY.

Yours,
Laurenz Albe

2012/2/15 Vojtěch Rylko <vojta.rylko@seznam.cz>:

this query performed so long and blocked table so I had to interrupt it. Is
there any way how to drop large indexes in non-blocking or /faster/ way?

Usually the problem is not with the size of the index -- but some
other running transactions that hold a read lock on the table, and
preventing the DROP INDEX from getting an exclusive lock. If the
exclusive lock is granted, the drop index is usually very fast.

Run 'select * from pg_stat_activity' and see if there are any "<IDLE>
in transaction" connections. It's normal to have these for a second or
few, but longer idle transactions usually indicate an application bug
-- it started a transaction, but "forgot" to rollback or commit. These
are problematic for this exact reason -- locks can't be released until
the transaction finishes.

Regards,
Marti

Albe Laurenz <laurenz.albe@wien.gv.at> wrote:

Vojtech Rylko wrote:

I need to drop some b-tree indexes because they are not used anymore.
Size of indexes vary between 700 MB and 7 GB. I tried common DROP
INDEX... but this query performed so long and blocked table so I had to
interrupt it. Is there any way how to drop large indexes in non-blocking
or /faster/ way?

Unfortunately not (yet).
PostgreSQL 9.2 will have DROP INDEX CONCURRENTLY.

Really? Great!

I have a use-case for that: an partial index, daily re-created (the
index based on the date and includes the last N days), and
sometimes we have trouble with this.

Andreas
--
Really, I'm not out to destroy Microsoft. That will just be a completely
unintentional side effect. (Linus Torvalds)
"If I was god, I would recompile penguin with --enable-fly." (unknown)
Kaufbach, Saxony, Germany, Europe. N 51.05082�, E 13.56889�

Dne 16.2.2012 9:53, Marti Raudsepp napsal(a):

2012/2/15 Vojtěch Rylko<vojta.rylko@seznam.cz>:

this query performed so long and blocked table so I had to interrupt it. Is
there any way how to drop large indexes in non-blocking or /faster/ way?

Usually the problem is not with the size of the index -- but some
other running transactions that hold a read lock on the table, and
preventing the DROP INDEX from getting an exclusive lock. If the
exclusive lock is granted, the drop index is usually very fast.

Run 'select * from pg_stat_activity' and see if there are any "<IDLE>
in transaction" connections. It's normal to have these for a second or
few, but longer idle transactions usually indicate an application bug
-- it started a transaction, but "forgot" to rollback or commit. These
are problematic for this exact reason -- locks can't be released until
the transaction finishes.

Regards,
Marti

Thanks! Caused by "IDLE in transaction". My nightmare solved. Droping 7
GB index in 2353 ms.

Regards,
Vojtěch R.