7714c63829
This simplifies the code a little bit. The new rule is that to update XLogCtl->LogwrtResult, you must hold both WALWriteLock and info_lck, whereas before we had two copies, one that was protected by WALWriteLock and another protected by info_lck. The code that updates them was already holding both locks, so merging the two is trivial. The third copy, XLogCtl->Insert.LogwrtResult, was not totally redundant, it was used in AdvanceXLInsertBuffer to update the backend-local copy, before acquiring the info_lck to read the up-to-date value. But the value of that seems dubious; at best it's saving one spinlock acquisition per completed WAL page, which is not significant compared to all the other work involved. And in practice, it's probably not saving even that much.
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