| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
| Cc: | "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: HeapTupleHeaderAdvanceLatestRemovedXid doing the wrong thing with multixacts |
| Date: | 2011-10-17 19:03:50 |
| Message-ID: | 17713.1318878230@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> I just noticed that HeapTupleHeaderAdvanceLatestRemovedXid is comparing Xmax as a TransactionId without verifying whether it is a multixact or not. Since they advance separately, this could lead to bogus answers. This probably needs to be fixed. I didn't look into past releases to see if there's a live released bug here or not.
> I think the fix is simply to ignore the Xmax if the HEAP_XMAX_IS_MULTI bit is set.
> Additionally I think it should check HEAP_XMAX_INVALID before reading the Xmax at all.
If it's failing to even check XMAX_INVALID, surely it's completely
broken? Perhaps it assumes its caller has checked all this?
regards, tom lane
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