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Commitd95e36d

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Remove obsolete nbtree split REDO routine comment.
Commitdd299df, which added suffix truncation to nbtree, simplifiedthe WAL record format used by page splits. It became necessary toexplicitly WAL-log the new high key for the left half of a split in allcases, which relieved the REDO routine from having to reconstruct a newhigh key for the left page by copying the first item from the rightpage. Remove a comment that referred to the previous practice.
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‎src/backend/access/nbtree/nbtxlog.c

Lines changed: 7 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -248,19 +248,16 @@ btree_xlog_split(bool onleft, XLogReaderState *record)
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PageSetLSN(rpage,lsn);
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MarkBufferDirty(rbuf);
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251-
/* don't release the buffer yet; we touch right page's first item below */
252-
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/* Now reconstruct left (original) sibling page */
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if (XLogReadBufferForRedo(record,0,&lbuf)==BLK_NEEDS_REDO)
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{
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/*
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* To retain the same physical order of the tuples that they had, we
258256
* initialize a temporary empty page for the left page and add all the
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* items to that in item number order. This mirrors how _bt_split()
260-
* works. It's not strictly required to retain the same physical
261-
* order, as long as the items are in the correct item number order,
262-
* but it helps debugging. See also _bt_restore_page(), which does
263-
* the same for the right page.
258+
* works. Retaining the same physical order makes WAL consistency
259+
* checking possible. See also _bt_restore_page(), which does the
260+
* same for the right page.
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*/
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Pagelpage= (Page)BufferGetPage(lbuf);
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BTPageOpaquelopaque= (BTPageOpaque)PageGetSpecialPointer(lpage);
@@ -345,7 +342,10 @@ btree_xlog_split(bool onleft, XLogReaderState *record)
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MarkBufferDirty(lbuf);
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}
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348-
/* We no longer need the buffers */
345+
/*
346+
* We no longer need the buffers. They must be released together, so that
347+
* readers cannot observe two inconsistent halves.
348+
*/
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if (BufferIsValid(lbuf))
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UnlockReleaseBuffer(lbuf);
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UnlockReleaseBuffer(rbuf);

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