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Commit4b8e24b

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Fix a couple of bugs with wal_log_hints.
1. Replay of the WAL record for setting a bit in the visibility mapcontained an assertion that a full-page image of that record type can onlyoccur with checksums enabled. But it can also happen with wal_log_hints, soremove the assertion. Unlike checksums, wal_log_hints can be changed on thefly, so it would be complicated to figure out if it was enabled at the timethat the WAL record was generated.2. wal_log_hints has the same effect on the locking needed to read the LSNof a page as data checksums. BufferGetLSNAtomic() didn't get the memo.Backpatch to 9.4, where wal_log_hints was added.
1 parentf7bb7f0 commit4b8e24b

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2 files changed

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‎src/backend/access/heap/heapam.c

Lines changed: 8 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -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
7482-
* map bit (unless checksums are enabled, in which case we must),
7483-
* because that would generate an unworkable volume of full-page
7484-
* writes. This exposes us to torn page hazards, but since we're not
7485-
* inspecting the existing page contents in any way, we don't care.
7482+
* map bit (unless checksums or wal_hint_bits is enabled, in which
7483+
* case we must), because that would generate an unworkable volume of
7484+
* 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
@@ -7497,10 +7498,10 @@ heap_xlog_visible(XLogReaderState *record)
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elseif (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
7501-
* 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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*/
7503-
Assert(DataChecksumsEnabled());
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}
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if (BufferIsValid(buffer))
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UnlockReleaseBuffer(buffer);

‎src/backend/storage/buffer/bufmgr.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -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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*/
2499-
if (!DataChecksumsEnabled()||BufferIsLocal(buffer))
2499+
if (!XLogHintBitIsNeeded()||BufferIsLocal(buffer))
25002500
returnPageGetLSN(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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