Bruce Momjian wrote: > > > I am not so concerned about this case but about other cases where we are > > > computing xid distances across the invalid range. > > > > Such as? > > Not sure. I have not had time to research this, but there might be > cases where this backward movement matters --- remember our XIDs are > valid only within about a 2 billion range, and we do less/greater > comparisons in that range (using a macro). That macro is not going to > cover over backward xid movement.
OK, I am done training for the day, and found this macro: /* advance a transaction ID variable, handling wraparound correctly */ #define TransactionIdAdvance(dest) \ do { \ (dest)++; \ if ((dest) < FirstNormalTransactionId) \ (dest) = FirstNormalTransactionId; \ } while(0) which seems OK, but we the -= all over varsup.c /* * We'll refuse to continue assigning XIDs in interactive mode once we get * within 1M transactions of data loss. This leaves lots of room for the * DBA to fool around fixing things in a standalone backend, while not * being significant compared to total XID space. (Note that since * vacuuming requires one transaction per table cleaned, we had better be * sure there's lots of XIDs left...) */ xidStopLimit = xidWrapLimit - 1000000; if (xidStopLimit < FirstNormalTransactionId) xidStopLimit -= FirstNormalTransactionId; Now I am not sure where to add a C comment. :-( -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers