On 2018-09-28 09:35:48 +0200, Peter Eisentraut wrote: > On 26/09/2018 23:48, Peter Eisentraut wrote: > > That's certainly a good argument. Note that if we implemented that the > > transaction timestamp is advanced inside procedures, that would also > > mean that the transaction timestamp as observed in pg_stat_activity > > would move during VACUUM, for example. That might or might not be > > desirable.
I think it doesn't hurt, although it's also not a huge advantage. > diff --git a/src/backend/access/transam/xact.c > b/src/backend/access/transam/xact.c > index 9aa63c8792..245735420c 100644 > --- a/src/backend/access/transam/xact.c > +++ b/src/backend/access/transam/xact.c > @@ -1884,14 +1884,19 @@ StartTransaction(void) > TRACE_POSTGRESQL_TRANSACTION_START(vxid.localTransactionId); > > /* > - * set transaction_timestamp() (a/k/a now()). We want this to be the > same > - * as the first command's statement_timestamp(), so don't do a fresh > - * GetCurrentTimestamp() call (which'd be expensive anyway). Also, mark > - * xactStopTimestamp as unset. > - */ > - xactStartTimestamp = stmtStartTimestamp; > - xactStopTimestamp = 0; > + * set transaction_timestamp() (a/k/a now()). Normally, we want this to > + * be the same as the first command's statement_timestamp(), so don't > do a > + * fresh GetCurrentTimestamp() call (which'd be expensive anyway). But > + * for transactions started inside statements (e.g., procedure calls), > we > + * want to advance the timestamp. > + */ > + if (xactStartTimestamp < stmtStartTimestamp) > + xactStartTimestamp = stmtStartTimestamp; > + else > + xactStartTimestamp = GetCurrentTimestamp(); > pgstat_report_xact_timestamp(xactStartTimestamp); > + /* Mark xactStopTimestamp as unset. */ > + xactStopTimestamp = 0; It's a bit weird to make this decision based on these two timestamps differing. For one, it only indirectly seems to be guaranteed that xactStartTimestamp is even set to anything here (to 0 by virtue of being a global var). Greetings, Andres Freund
