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Merge copies of converting an XID to a FullTransactionId.

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Assume twophase.c is the performance-sensitive caller, and preserve its
choice of unlikely() branch hint.  Add some retrospective rationale for
that choice.  Back-patch to v17, for the next commit to use it.

Reviewed (in earlier versions) by Michael Paquier.

Discussion: https://postgr.es/m/17821-dd8c334263399284@postgresql.org
Discussion: https://postgr.es/m/20250116010051.f3.nmisch@google.com
This commit is contained in:
Noah Misch
2025-01-25 11:28:14 -08:00
parent 4f6ec3831d
commit 81772a495e
5 changed files with 77 additions and 93 deletions
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18
src/backend/access/transam/xlogreader.c
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@@ -2166,28 +2166,14 @@ RestoreBlockImage(XLogReaderState *record, uint8 block_id, char *page)
FullTransactionId
XLogRecGetFullXid(XLogReaderState *record)
{
TransactionId xid,
next_xid;
uint32 epoch;
/*
* This function is only safe during replay, because it depends on the
* replay state. See AdvanceNextFullTransactionIdPastXid() for more.
*/
Assert(AmStartupProcess() || !IsUnderPostmaster);
xid = XLogRecGetXid(record);
next_xid = XidFromFullTransactionId(TransamVariables->nextXid);
epoch = EpochFromFullTransactionId(TransamVariables->nextXid);
/*
* If xid is numerically greater than next_xid, it has to be from the last
* epoch.
*/
if (unlikely(xid > next_xid))
--epoch;
return FullTransactionIdFromEpochAndXid(epoch, xid);
return FullTransactionIdFromAllowableAt(TransamVariables->nextXid,
XLogRecGetXid(record));
}
#endif