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, and all get inserted into a temp table. 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 could figure it out empirically, but the queries are really slow on my dev laptop and I don't have access to the staging system at the moment. Also, it requires revamping a fair bit of code, so I figured it never hurts to ask. I don't have a sense of whether postgres is able to parallelize multiple subqueries via a single scan
You don't indicate how complex your queries are. If it's just a single table and the conditions are relatively simple, could you do something like this? insert into (...) select ... where (...) OR (...) OR (...) Craig -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
