Chris Browne <cbbrowne@xxxxxxx> writes: > 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. You're right that a read-only transaction doesn't generate an XID. But that is not a function of whether you do SET TRANSACTION READ ONLY; it's a function of refraining from attempting any database changes. The SET might be useful for clarifying and enforcing your intent, but it's not a performance boost to use it, versus just doing the read-only transaction without it. Also, I believe that SET TRANSACTION READ ONLY isn't a "hard" read only restriction anyway --- it'll still allow writes to temp tables for example, which will cause assignment of an XID. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
