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.
Someone might match the xid with xids found on disk. If we replace the
xid with the vid, than this is impossible unless you also periodically
snapshot pg_locks.

I suppose there's no great harm in providing %v as an additional
prefix format code ...
Ok, I'll do this. Shouldn't be too hard, it seems...

BTW, my current patch doesn't show the vid in pg_stat_activity.

Hmm, actually it looks like the join key for that is supposed to be PID,
so maybe we needn't do anything to it.
Yes, that was my reasoning too. Maybe we want to add both xid and vid
to pg_stat_activity one day, but since this patch might hit 8.3, lets
keep it as minimal as possible...

Even in the case of a conflict, two transactions still wouldn't be
running with the same vid. Rather, the second one would block until
the first exits, because we hold an ExclusiveLock on the vid.

It's definitely sufficient then ...
This implies that connecting and the immediately starting a transaction
(which will then get "1" as it's localTransactionId) which you keep
open *will* block some other transaction after 4 billion other connects.

I'm not saying that this is unacceptable, I just wanted to clearly state
the consequences.

greetings, Florian Pflug

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