PG loads data at the block level to shared_buffers. Most likely it is because the second sql selects different set of rows (from different blocks) than the first sql. On Fri, Mar 18, 2016 at 4:24 PM, Paul Jones <pbj@xxxxxxxxxx> wrote: > In Postgres 9.5.1 with a shared_buffer cache of 7Gb, a SELECT from > a single table that uses an index appears to read the table into the > shared_buffer cache. Then, as many times as the exact same SELECT is > repeated in the same session, it runs blazingly fast and doesn't even > touch the disk. All good. > > Now, in the *same* session, if a different SELECT from the *same* table, > using the *same* index is run, it appears to read the entire table from > disk again. > > Why is this? Is there something about the query that qualifies the > contents of the share_buffer cache? Would this act differently for > different kinds of indexes? > > PJ > > > -- > Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
