Fix a couple of bugs with wal_log_hints.
1. Replay of the WAL record for setting a bit in the visibility map contained an assertion that a full-page image of that record type can only occur with checksums enabled. But it can also happen with wal_log_hints, so remove the assertion. Unlike checksums, wal_log_hints can be changed on the fly, so it would be complicated to figure out if it was enabled at the time that the WAL record was generated. 2. wal_log_hints has the same effect on the locking needed to read the LSN of a page as data checksums. BufferGetLSNAtomic() didn't get the memo. Backpatch to 9.4, where wal_log_hints was added.
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@ -7479,10 +7479,11 @@ heap_xlog_visible(XLogReaderState *record)
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{
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/*
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* We don't bump the LSN of the heap page when setting the visibility
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* map bit (unless checksums are enabled, in which case we must),
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* because that would generate an unworkable volume of full-page
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* writes. This exposes us to torn page hazards, but since we're not
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* inspecting the existing page contents in any way, we don't care.
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* map bit (unless checksums or wal_hint_bits is enabled, in which
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* case we must), because that would generate an unworkable volume of
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* full-page writes. This exposes us to torn page hazards, but since
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* we're not inspecting the existing page contents in any way, we
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* don't care.
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*
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* However, all operations that clear the visibility map bit *do* bump
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* the LSN, and those operations will only be replayed if the XLOG LSN
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@ -7497,10 +7498,10 @@ heap_xlog_visible(XLogReaderState *record)
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else if (action == BLK_RESTORED)
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{
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/*
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* If heap block was backed up, restore it. This can only happen with
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* checksums enabled.
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* If heap block was backed up, we already restored it and there's
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* nothing more to do. (This can only happen with checksums or
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* wal_log_hints enabled.)
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*/
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Assert(DataChecksumsEnabled());
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}
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if (BufferIsValid(buffer))
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UnlockReleaseBuffer(buffer);
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@ -2496,7 +2496,7 @@ BufferGetLSNAtomic(Buffer buffer)
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/*
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* If we don't need locking for correctness, fastpath out.
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*/
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if (!DataChecksumsEnabled() || BufferIsLocal(buffer))
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if (!XLogHintBitIsNeeded() || BufferIsLocal(buffer))
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return PageGetLSN(page);
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/* Make sure we've got a real buffer, and that we hold a pin on it. */
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