On 04/09/2017 08:05 AM, Job wrote:
Hi, i have a table with about 400 millions of rows and i need to build some aggregate function for reporting. I noticed that query performances are slowing down, even though indexes are present. Query is simple (i make an example, my table is in italian language): select a,sum(b) from table where a=x and c=y group by a a is a varchar b is an integer x and y are two field i use for filter results. I tried to create different indexes to try to speed up performance: index1 (a) index2 (c) index3 (a,c) I noticed, with query planner, that the mulfi-field index is not used. Postgresql 9.6.1 still use scan without indexes.
At some point doing a scan over a table is better then using an index, as index use incurs a lookup cost. Unfortunately there is no way to determine what is actually happening in your case without more information.
So: 1) Table schema(language does not matter, the names are just tags). 2) The actual query run through EXPLAIN ANALYZE.
I obtain significant improvements only if i create a materialized view with aggregated data. But i would like to avoid - if possible - creating (and mantaining) the materialized view. Than you! /F
-- Adrian Klaver adrian.klaver@xxxxxxxxxxx -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
