Update btree_xlog_delete() comments.

Commit fe97c61c updated LP_DEAD item deletion comments, but missed a
minor discrepancy on the REDO side.  Fix it now.

In passing, don't talk about the btree_xlog_vacuum() behavior within
btree_xlog_delete().  The reliance on XLOG_HEAP2_CLEANUP_INFO records
for recovery conflicts is already discussed within btvacuumpage() and
mentioned again in passing above btree_xlog_vacuum(), which seems
sufficient.

diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c
index f9e94c28c5b85703cccafa47c708c0b77fc3889d..8376a5e6b75946418d702ce6dec3a6fcf16af60a 100644 (file)
--- a/src/backend/access/nbtree/nbtree.c
+++ b/src/backend/access/nbtree/nbtree.c
@@ -1208,9 +1208,10 @@ restart:
                 * as long as the callback function only considers whether the
                 * index tuple refers to pre-cutoff heap tuples that were
                 * certainly already pruned away during VACUUM's initial heap
-                * scan by the time we get here. (We can rely on conflicts
-                * produced by heap pruning, rather than producing our own
-                * now.)
+                * scan by the time we get here. (XLOG_HEAP2_CLEANUP_INFO
+                * records produce conflicts using a latestRemovedXid value
+                * for the entire VACUUM, so there is no need to produce our
+                * own conflict now.)
                 *
                 * Backends with snapshots acquired after a VACUUM starts but
                 * before it finishes could have a RecentGlobalXmin with a

diff --git a/src/backend/access/nbtree/nbtxlog.c b/src/backend/access/nbtree/nbtxlog.c
index 72d8432d3c202bfc63f0e28ba5e1614495f05abd..5eca4ab2727879065e26cd612ac15b3f2209ccc4 100644 (file)
--- a/src/backend/access/nbtree/nbtxlog.c
+++ b/src/backend/access/nbtree/nbtxlog.c
@@ -428,14 +428,7 @@ btree_xlog_delete(XLogReaderState *record)
 
    /*
     * If we have any conflict processing to do, it must happen before we
-    * update the page.
-    *
-    * Btree delete records can conflict with standby queries.  You might
-    * think that vacuum records would conflict as well, but we've handled
-    * that already.  XLOG_HEAP2_CLEANUP_INFO records provide the highest xid
-    * cleaned by the vacuum of the heap and so we can resolve any conflicts
-    * just once when that arrives.  After that we know that no conflicts
-    * exist from individual btree vacuum records on that index.
+    * update the page
     */
    if (InHotStandby)
    {
@@ -463,10 +456,7 @@ btree_xlog_delete(XLogReaderState *record)
            PageIndexMultiDelete(page, unused, xlrec->nitems);
        }
 
-       /*
-        * Mark the page as not containing any LP_DEAD items --- see comments
-        * in _bt_delitems_delete().
-        */
+       /* Mark the page as not containing any LP_DEAD items */
        opaque = (BTPageOpaque) PageGetSpecialPointer(page);
        opaque->btpo_flags &= ~BTP_HAS_GARBAGE;