Re: the XID question

Andres Freund <andres@anarazel.de> wrote:
> On Wednesday, January 19, 2011 07:06:58 PM Chris Browne wrote:

>> A read-only transaction won't consume XIDs, but if you don't
>> expressly declare it read-only, they're still liable to get
>> eaten...
> No. The Xid is generally only allocated at the first place a real
> xid is needed. See GetCurrentTransactionId, AssignTransactionId in
> xact.c and the caller of the former.

Or just test it in psql.  BEGIN, run your query, look at pg_locks.
If an xid has been assigned, you'll see it there in the
transactionid column.  You can easily satisfy yourself which
statements grab an xid....

-Kevin