Re: [PATCHES] [pgsql-patches] Phantom Command IDs, updated patch

Bruce Momjian <bruce@momjian.us> writes:
> The way combo cid is supposed to work is that you are deleting a row
> created in your same transaction by a previous command id, so you look
> in the combo cid array to see if a match for that pair exists --- if
> not, you create a new entry and put the two cids on it.

> So, with the combo lock cid, you do the same process, and lookups of who
> holds the lock looks at the cid combo, and if the second subtransaction
> was aborted, the first one is the lock holder.  If you again lock the
> row, you create a new combo cid and use the original cid there because
> the second cid was aborted.

No, because no process other than the originator can see the combo-cid
data structure, and for locking situations you really need other
backends to be able to know whether the tuple is locked and how.

But I think my proposal of extending MultiXact would fix it; please look
at that.
        regards, tom lane