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Update PruneState.all_[visible|frozen] earlier in pruning
During pruning and freezing in phase I of vacuum, we delay clearing
all_visible and all_frozen in the presence of dead items. This allows
opportunistic freezing if the page would otherwise be fully frozen,
since those dead items are later removed in vacuum phase III.
To move the VM update into the same WAL record that
prunes and freezes tuples, we must know whether the page will
be marked all-visible/all-frozen before emitting WAL. Previously we
waited until after emitting WAL to update all_visible/all_frozen to
their correct values.
The only barrier to updating these flags immediately after deciding
whether to opportunistically freeze was that while emitting WAL for a
record freezing tuples, we use the pre-corrected value of all_frozen to
compute the snapshot conflict horizon. By determining the conflict
horizon earlier, we can update the flags immediately after making the
opportunistic freeze decision.
This is required to set the VM in the XLOG_HEAP2_PRUNE_VACUUM_SCAN
record emitted by pruning and freezing.
Author: Melanie Plageman <[email protected]>
Reviewed-by: Kirill Reshke <[email protected]>
Discussion: https://postgr.es/m/flat/CAAKRu_ZMw6Npd_qm2KM%2BFwQ3cMOMx1Dh3VMhp8-V7SOLxdK9-g%40mail.gmail.com
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