jnelson+pgsql@xxxxxxxxxxx (Jon Nelson) writes: > Are there any performance implications (benefits) to executing queries > in a transaction where > SET TRANSACTION READ ONLY; > has been executed? Directly? No. Indirectly, well, a *leetle* bit... Transactions done READ ONLY do not generate actual XIDs, which reduces the amount of XID generation (pretty tautological!), which reduces the need to do VACUUM to protect against XID wraparound. <http://www.postgresql.org/docs/8.4/static/routine-vacuuming.html#VACUUM-BASICS> If you process 50 million transactions, that chews thru 50 million XIDs. If 45 million of those were processed via READ ONLY transactions, then the same processing only chews thru 5 million XIDs, meaning that the XID-relevant vacuums can be done rather less frequently. This only terribly much matters if: a) your database is so large that there are tables on which VACUUM would run for a very long time, and b) you are chewing through XIDs mighty quickly. If either condition isn't true, then the indirect effect isn't important either. -- let name="cbbrowne" and tld="gmail.com" in name ^ "@" ^ tld;; "I'm not switching from slrn. I'm quite confident that anything that *needs* to be posted in HTML is fatuous garbage not worth my time." -- David M. Cook <davecook@xxxxxxxx> -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
