Re: Automatic free space map filling

Alvaro Herrera wrote:
> Bruce Momjian wrote:
> > Alvaro Herrera wrote:
> > > Csaba Nagy wrote:
> > > 
> > > > Now when the queue tables get 1000 times dead space compared to their
> > > > normal size, I get performance problems. So tweaking vacuum cost delay
> > > > doesn't buy me anything, as not vacuum per se is the performance
> > > > problem, it's long run time for big tables is.
> > > 
> > > So for you it would certainly help a lot to be able to vacuum the first
> > > X pages of the big table, stop, release locks, create new transaction,
> > > continue with the next X pages, lather, rinse, repeat.
> > 
> > But what about index clearing?  When do you scan each index?
> 
> At the end of each iteration (or earlier, depending on
> maintenance_work_mem).  So for each iteration you would need to scan the
> indexes.
> 
> Maybe we could make maintenance_work_mem be the deciding factor; after
> scanning the indexes, do the release/reacquire locks cycle.

Ewe.  How expensive is scanning an index compared to the heap?  Does
anyone have figure on that in terms of I/O and time?

--  Bruce Momjian   http://candle.pha.pa.us SRA OSS, Inc.   http://www.sraoss.com
 + If your life is a hard drive, Christ can be your backup. +