[PERFORM] multiple table scan performance

2011-03-29 Thread Samuel Gendler
I've got some functionality that necessarily must scan a relatively large table. Even worse, the total workload is actually 3 similar, but different queries, each of which requires a table scan. They all have a resultset that has the same structure, and all get inserted into a temp table. Is the

Re: [PERFORM] multiple table scan performance

2011-03-29 Thread Claudio Freire
On Tue, Mar 29, 2011 at 7:16 PM, Samuel Gendler wrote: > Is there any performance benefit to revamping the workload such that it issues > a single: > insert into (...) select ... UNION select ... UNION select > as opposed to 3 separate "insert into () select ..." statements. I wouldn't expect any

Re: [PERFORM] multiple table scan performance

2011-03-29 Thread Marti Raudsepp
On Wed, Mar 30, 2011 at 01:16, Samuel Gendler wrote: > I've got some functionality that necessarily must scan a relatively large > table > Is there any performance benefit to revamping the workload such that it issues > a single: > insert into (...) select ... UNION select ... UNION select > as

Re: [PERFORM] multiple table scan performance

2011-03-29 Thread Samuel Gendler
On Tue, Mar 29, 2011 at 5:05 PM, Marti Raudsepp wrote: > On Wed, Mar 30, 2011 at 01:16, Samuel Gendler > wrote: > > You can trick Postgres (8.3.x and newer) into doing it in parallel > anyway: open 3 separate database connections and issue each of these > 'INSERT INTO ... SELECT' parts separatel

Re: [PERFORM] multiple table scan performance

2011-03-29 Thread Craig James
On 3/29/11 3:16 PM, Samuel Gendler wrote: I've got some functionality that necessarily must scan a relatively large table. Even worse, the total workload is actually 3 similar, but different queries, each of which requires a table scan. They all have a resultset that has the same structure,