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Remove obsolete nbtree split REDO routine comment.

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Commit dd299df8189, which added suffix truncation to nbtree, simplified
the WAL record format used by page splits.  It became necessary to
explicitly WAL-log the new high key for the left half of a split in all
cases, which relieved the REDO routine from having to reconstruct a new
high key for the left page by copying the first item from the right
page.  Remove a comment that referred to the previous practice.
This commit is contained in:
Peter Geoghegan 2019-05-08 12:47:20 -07:00
parent 61639816b8
commit d95e36dc38
1 changed files with 7 additions and 7 deletions
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14
src/backend/access/nbtree/nbtxlog.c
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@ -248,8 +248,6 @@ btree_xlog_split(bool onleft, XLogReaderState *record)
PageSetLSN(rpage, lsn); PageSetLSN(rpage, lsn);
MarkBufferDirty(rbuf); MarkBufferDirty(rbuf);
/* don't release the buffer yet; we touch right page's first item below */
/* Now reconstruct left (original) sibling page */ /* Now reconstruct left (original) sibling page */
if (XLogReadBufferForRedo(record, 0, &lbuf) == BLK_NEEDS_REDO) if (XLogReadBufferForRedo(record, 0, &lbuf) == BLK_NEEDS_REDO)
{ {
@ -257,10 +255,9 @@ btree_xlog_split(bool onleft, XLogReaderState *record)
* To retain the same physical order of the tuples that they had, we * To retain the same physical order of the tuples that they had, we
* initialize a temporary empty page for the left page and add all the * initialize a temporary empty page for the left page and add all the
* items to that in item number order. This mirrors how _bt_split() * items to that in item number order. This mirrors how _bt_split()
* works. It's not strictly required to retain the same physical * works. Retaining the same physical order makes WAL consistency
* order, as long as the items are in the correct item number order, * checking possible. See also _bt_restore_page(), which does the
* but it helps debugging. See also _bt_restore_page(), which does * same for the right page.
* the same for the right page.
*/ */
Page lpage = (Page) BufferGetPage(lbuf); Page lpage = (Page) BufferGetPage(lbuf);
BTPageOpaque lopaque = (BTPageOpaque) PageGetSpecialPointer(lpage); BTPageOpaque lopaque = (BTPageOpaque) PageGetSpecialPointer(lpage);
@ -345,7 +342,10 @@ btree_xlog_split(bool onleft, XLogReaderState *record)
MarkBufferDirty(lbuf); MarkBufferDirty(lbuf);
} }
/* We no longer need the buffers */ /*
* We no longer need the buffers. They must be released together, so that
* readers cannot observe two inconsistent halves.
*/
if (BufferIsValid(lbuf)) if (BufferIsValid(lbuf))
UnlockReleaseBuffer(lbuf); UnlockReleaseBuffer(lbuf);
UnlockReleaseBuffer(rbuf); UnlockReleaseBuffer(rbuf);