Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>He means that the tuple that heap_update moves to page 1 (which will no
>longer be processed by vacuum) will contain a multixact that's older
>than relminmxid -- because it is copied unchanged by heap_update instead
>of properly checking against age limit.
I see. The problem is more or less with this heap_update() code:
/* * And also prepare an Xmax value for the new copy of the tuple. If there * was no xmax previously, or
therewas one but all lockers are now gone, * then use InvalidXid; otherwise, get the xmax from the old tuple. (In
* rare cases that might also be InvalidXid and yet not have the * HEAP_XMAX_INVALID bit set; that's fine.) */
if((oldtup.t_data->t_infomask & HEAP_XMAX_INVALID) || HEAP_LOCKED_UPGRADED(oldtup.t_data->t_infomask) ||
(checked_lockers&& !locker_remains)) xmax_new_tuple = InvalidTransactionId; else xmax_new_tuple =
HeapTupleHeaderGetRawXmax(oldtup.t_data);
My naive guess is that we have to create a new MultiXactId here in at
least some cases, just like FreezeMultiXactId() sometimes does.
--
Peter Geoghegan
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