On Sat, 14 Feb 2009, Alexander Staubo wrote:
Are there any statistics, either in PostgreSQL proper or in the OS, that I can use as metrics to guide the tuning? For example, is there anything in pg_stat_bgwriter that can help me tune the bgwriter_lru_* settings?
http://www.westnet.com/~gsmith/content/postgresql/chkp-bgw-83.htm goes over this topic, with "Appendix B: pg_stat_bgwriter sample analysis" covering a look at what to do based on a pg_stat_bgwriter snapshot.
Do transactions that only contain query statements end up writing entries to the WAL when they commit?
You need a transactions XID before you can write to the WAL, and quoting from the transaction management docs:
"Transactions and subtransactions are assigned permanent XIDs only when/if they first do something that requires one --- typically, insert/update/delete a tuple"
The main thing that will cause writes even when reading are hint bit updates, which have been mentioned here already. http://wiki.postgresql.org/wiki/Hint_Bits has an intro to that topic.
-- * Greg Smith gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
