Fix backup-block numbering in redo of b-tree split.

I got the backup block numbers off-by-one in the commit that changed the
way incomplete-splits are handled. I blame the comments, which said
"backup block 1" and "backup block 2", even though the backup blocks
are numbered starting from 0, in the macros and functions used in replay.
Fix the comments and the code.

Per Jeff Janes' bug report about corruption caused by torn page writes.
The incorrect code is new in git master, but backpatch the comment change
down to 9.0, where the numbering in the redo-side macros  was changed.

diff --git a/src/backend/access/nbtree/nbtinsert.c b/src/backend/access/nbtree/nbtinsert.c
index d64cbd98223f4a8c97d3acbb90d9aa29406ca1c1..ecee5ac7f665fa42c7cb1d58e19f695f8cae0aa0 100644 (file)
--- a/src/backend/access/nbtree/nbtinsert.c
+++ b/src/backend/access/nbtree/nbtinsert.c
@@ -1299,7 +1299,7 @@ _bt_split(Relation rel, Buffer buf, Buffer cbuf, OffsetNumber firstright,
 
            lastrdata->data = (char *) newitem;
            lastrdata->len = MAXALIGN(newitemsz);
-           lastrdata->buffer = buf;    /* backup block 1 */
+           lastrdata->buffer = buf;    /* backup block 0 */
            lastrdata->buffer_std = true;
        }
 
@@ -1320,7 +1320,7 @@ _bt_split(Relation rel, Buffer buf, Buffer cbuf, OffsetNumber firstright,
            item = (IndexTuple) PageGetItem(origpage, itemid);
            lastrdata->data = (char *) item;
            lastrdata->len = MAXALIGN(IndexTupleSize(item));
-           lastrdata->buffer = buf;    /* backup block 1 */
+           lastrdata->buffer = buf;    /* backup block 0 */
            lastrdata->buffer_std = true;
        }
 
@@ -1333,11 +1333,11 @@ _bt_split(Relation rel, Buffer buf, Buffer cbuf, OffsetNumber firstright,
             * Although we don't need to WAL-log anything on the left page, we
             * still need XLogInsert to consider storing a full-page image of
             * the left page, so make an empty entry referencing that buffer.
-            * This also ensures that the left page is always backup block 1.
+            * This also ensures that the left page is always backup block 0.
             */
            lastrdata->data = NULL;
            lastrdata->len = 0;
-           lastrdata->buffer = buf;    /* backup block 1 */
+           lastrdata->buffer = buf;    /* backup block 0 */
            lastrdata->buffer_std = true;
        }
 
@@ -1353,7 +1353,7 @@ _bt_split(Relation rel, Buffer buf, Buffer cbuf, OffsetNumber firstright,
            cblkno = BufferGetBlockNumber(cbuf);
            lastrdata->data = (char *) &cblkno;
            lastrdata->len = sizeof(BlockNumber);
-           lastrdata->buffer = cbuf;   /* backup block 2 */
+           lastrdata->buffer = cbuf;   /* backup block 1 */
            lastrdata->buffer_std = true;
        }
 
@@ -1386,7 +1386,7 @@ _bt_split(Relation rel, Buffer buf, Buffer cbuf, OffsetNumber firstright,
 
            lastrdata->data = NULL;
            lastrdata->len = 0;
-           lastrdata->buffer = sbuf;   /* bkp block 2 (leaf) or 3 (non-leaf) */
+           lastrdata->buffer = sbuf;   /* bkp block 1 (leaf) or 2 (non-leaf) */
            lastrdata->buffer_std = true;
        }
 

diff --git a/src/backend/access/nbtree/nbtxlog.c b/src/backend/access/nbtree/nbtxlog.c
index 640639c175e58286da4a18ed1058e6f46d23c4a7..5f9fc49e78ca1388ab482e24c8b5a873238ae0b6 100644 (file)
--- a/src/backend/access/nbtree/nbtxlog.c
+++ b/src/backend/access/nbtree/nbtxlog.c
@@ -300,8 +300,8 @@ btree_xlog_split(bool onleft, bool isroot,
     */
    if (!isleaf)
    {
-       if (record->xl_info & XLR_BKP_BLOCK(2))
-           (void) RestoreBackupBlock(lsn, record, 2, false, false);
+       if (record->xl_info & XLR_BKP_BLOCK(1))
+           (void) RestoreBackupBlock(lsn, record, 1, false, false);
        else
            _bt_clear_incomplete_split(lsn, record, xlrec->node, cblkno);
    }
@@ -439,10 +439,10 @@ btree_xlog_split(bool onleft, bool isroot,
    if (xlrec->rnext != P_NONE)
    {
        /*
-        * the backup block containing right sibling is 2 or 3, depending
+        * the backup block containing right sibling is 1 or 2, depending
         * whether this was a leaf or internal page.
         */
-       int         rnext_index = isleaf ? 2 : 3;
+       int         rnext_index = isleaf ? 1 : 2;
 
        if (record->xl_info & XLR_BKP_BLOCK(rnext_index))
            (void) RestoreBackupBlock(lsn, record, rnext_index, false, false);