Add WAL consistency checking facility.

When the new GUC wal_consistency_checking is set to a non-empty value,
it triggers recording of additional full-page images, which are
compared on the standby against the results of applying the WAL record
(without regard to those full-page images).  Allowable differences
such as hints are masked out, and the resulting pages are compared;
any difference results in a FATAL error on the standby.

Kuntal Ghosh, based on earlier patches by Michael Paquier and Heikki
Linnakangas.  Extensively reviewed and revised by Michael Paquier and
by me, with additional reviews and comments from Amit Kapila, Álvaro
Herrera, Simon Riggs, and Peter Eisentraut.

1 files changed, 79 insertions, 0 deletions

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 5fd7f1e1a20..0be48fb3ee1 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -38,6 +38,7 @@
  */
 #include "postgres.h"
 
+#include "access/bufmask.h"
 #include "access/heapam.h"
 #include "access/heapam_xlog.h"
 #include "access/hio.h"
@@ -9142,3 +9143,81 @@ heap_sync(Relation rel)
 		heap_close(toastrel, AccessShareLock);
 	}
 }
+
+/*
+ * Mask a heap page before performing consistency checks on it.
+ */
+void
+heap_mask(char *pagedata, BlockNumber blkno)
+{
+	Page		page = (Page) pagedata;
+	OffsetNumber off;
+
+	mask_page_lsn(page);
+
+	mask_page_hint_bits(page);
+	mask_unused_space(page);
+
+	for (off = 1; off <= PageGetMaxOffsetNumber(page); off++)
+	{
+		ItemId		iid = PageGetItemId(page, off);
+		char	   *page_item;
+
+		page_item = (char *) (page + ItemIdGetOffset(iid));
+
+		if (ItemIdIsNormal(iid))
+		{
+
+			HeapTupleHeader page_htup = (HeapTupleHeader) page_item;
+
+			/*
+			 * If xmin of a tuple is not yet frozen, we should ignore
+			 * differences in hint bits, since they can be set without
+			 * emitting WAL.
+			 */
+			if (!HeapTupleHeaderXminFrozen(page_htup))
+				page_htup->t_infomask &= ~HEAP_XACT_MASK;
+			else
+			{
+				/* Still we need to mask xmax hint bits. */
+				page_htup->t_infomask &= ~HEAP_XMAX_INVALID;
+				page_htup->t_infomask &= ~HEAP_XMAX_COMMITTED;
+			}
+
+			/*
+			 * During replay, we set Command Id to FirstCommandId. Hence, mask
+			 * it. See heap_xlog_insert() for details.
+			 */
+			page_htup->t_choice.t_heap.t_field3.t_cid = MASK_MARKER;
+
+			/*
+			 * For a speculative tuple, heap_insert() does not set ctid in the
+			 * caller-passed heap tuple itself, leaving the ctid field to
+			 * contain a speculative token value - a per-backend monotonically
+			 * increasing identifier. Besides, it does not WAL-log ctid under
+			 * any circumstances.
+			 *
+			 * During redo, heap_xlog_insert() sets t_ctid to current block
+			 * number and self offset number. It doesn't care about any
+			 * speculative insertions in master. Hence, we set t_ctid to
+			 * current block number and self offset number to ignore any
+			 * inconsistency.
+			 */
+			if (HeapTupleHeaderIsSpeculative(page_htup))
+				ItemPointerSet(&page_htup->t_ctid, blkno, off);
+		}
+
+		/*
+		 * Ignore any padding bytes after the tuple, when the length of the
+		 * item is not MAXALIGNed.
+		 */
+		if (ItemIdHasStorage(iid))
+		{
+			int			len = ItemIdGetLength(iid);
+			int			padlen = MAXALIGN(len) - len;
+
+			if (padlen > 0)
+				memset(page_item + len, MASK_MARKER, padlen);
+		}
+	}
+}