On Sun, Oct 22, 2017 at 9:23 PM, Eric Ridge <eeb...@gmail.com> wrote:
> When sitting inside an extension, and given an arbitrary TransactionId, how
> can you determine that it aborted/crashed *and* that no other active
> transaction thinks it is still running?
>
> I've tried to answer this question myself (against the 9.3 sources), and it
> seems like it's just:
>
> {
> TransactionId oldestXmin = GetOldestXmin (false, false);
> TransactionId xid = 42;
>
> if (TransactionIdPrecedes(xid, oldestXmin) &&
> !TransactionIdDidCommit(xid) &&
> !TransactionIdIsInProgress(xid)) /* not even sure this is necessary? */
> {
> /* xid is aborted/crashed and no active transaction cares */
> }
> }
>
> Can anyone confirm or deny that this is correct? I feel like it is correct,
> but I'm no expert.
I think TransactionIdPrecedes(xid, oldestXmin) &&
!TransactionIdDidCommit(xid) is sufficient. If the transaction ID
precedes oldestXmin, then it's either committed or aborted; no other
state is possible. If it didn't commit, it aborted, and it is right
to test that using !TransactionIdDidCommit(xid) since commits are
always recorded but aborts are only usually recorded.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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