Heikki Linnakangas wrote:
Tom Lane wrote:
"Florian G. Pflug" <[EMAIL PROTECTED]> writes:
Tom Lane wrote:
"Heikki Linnakangas" <[EMAIL PROTECTED]> writes:
Should there be new a log_line_prefix percent code for virtual
transaction ids? Or should we change the meaning of %x to be virtual
transaction id instead of the real one.
I think the latter should be sufficient, especially if we also are showing
vxid in pg_locks and pg_stat_activity.
Hm.. Wouldn't that kind of defeat the idea of a log, if you need the
output of pg_locks to interpret it? Maybe we should just show both
values for %x? Or just the xid if it's set, and the vid otherwise?
Well, how do you interpret xid in the log today, if not by reference
to those views?  The last option seems quite unworkable, especially
for CSV-based logs.


I don't think people usually interpret the xid in logs in any way. It's
just a handy unique (unique enough, ignoring xid wraparound) identifier
for the transaction that you can use to figure out what each separate
transaction is doing. For that purpose, it doesn't matter if it doesn't
match the normal on-disk xid, using vid instead of xid works just fine.

Hmm. Or is it unique enough after all? Do we reuse session ids after a
server restart?
Yes - the sessionIs is just a counter in shared memory, so we start "1"
after a restart again.

For debugging PostgreSQL bugs, though, having the real xid in the logs
is really nice. You can then compare the logs against the tuples on the
disk.
I take this as a vote for having both "%x" and "%v" for xid and virtual xid
respectively.

greetings, Florian Pflug

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