Re: 10+hrs vs 15min because of just one index

On 2/10/06, Aaron Turner <synfinatic@gmail.com> wrote:
> So I'm trying to figure out how to optimize my PG install (8.0.3) to
> get better performance without dropping one of my indexes.
> Basically, I have a table of 5M records with 3 columns:
> pri_key (SERIAL)
> data char(48)
> groupid integer
> there is an additional unique index on the data column.
> The problem is that when I update the groupid column for all the
> records, the query takes over 10hrs (after that I just canceled the
> update).  Looking at iostat, top, vmstat shows I'm horribly disk IO
> bound (for data not WAL, CPU 85-90% iowait) and not swapping.
> Dropping the unique index on data (which isn't used in the query),

for such a large update i would suggest to go with different scenario:
split update into packets (10000, or 50000 rows at the time)
and do:
update packet
vacuum table
for all packets. and then reindex the table. should work much nicer.

depesz