From fce43ad9d1f85e793bbcfc21efd796fbe4fa9b2a Mon Sep 17 00:00:00 2001
From: Peter Geoghegan <pg@bowt.ie>
Date: Tue, 18 Sep 2018 18:18:55 -0700
Subject: [PATCH v5 2/3] Add temporary page split debug LOG instrumentation.

LOGs details on the new left high key in the event of a leaf page split.
This is an easy way to directly observe the effectiveness of suffix
truncation as it happens, which was useful during development.  The
macro DEBUG_SPLITS must be defined (uncommented) for the instrumentation
to be enabled.
---
 src/backend/access/nbtree/nbtinsert.c | 69 +++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/src/backend/access/nbtree/nbtinsert.c b/src/backend/access/nbtree/nbtinsert.c
index 0cb8bb1816..598e702bf1 100644
--- a/src/backend/access/nbtree/nbtinsert.c
+++ b/src/backend/access/nbtree/nbtinsert.c
@@ -27,6 +27,11 @@
 #include "utils/datum.h"
 #include "utils/tqual.h"
 
+/* #define DEBUG_SPLITS */
+#ifdef DEBUG_SPLITS
+#include "catalog/catalog.h"
+#endif
+
 /* Minimum tree height for application of fastpath optimization */
 #define BTREE_FASTPATH_MIN_LEVEL	2
 #define STACK_SPLIT_POINTS			15
@@ -1287,9 +1292,64 @@ _bt_split(Relation rel, Buffer buf, Buffer cbuf, OffsetNumber firstright,
 		lefthikey = _bt_suffix_truncate(rel, lastleft, item);
 		itemsz = IndexTupleSize(lefthikey);
 		itemsz = MAXALIGN(itemsz);
+#ifdef DEBUG_SPLITS
+		if (IsNormalProcessingMode() && !IsSystemRelation(rel))
+		{
+			TupleDesc	itupdesc = RelationGetDescr(rel);
+			Datum		values[INDEX_MAX_KEYS];
+			bool		isnull[INDEX_MAX_KEYS];
+			char	   *lastleftstr;
+			char	   *firstrightstr;
+			char	   *newstr;
+
+			index_deform_tuple(lastleft, itupdesc, values, isnull);
+			lastleftstr = BuildIndexValueDescription(rel, values, isnull);
+			index_deform_tuple(item, itupdesc, values, isnull);
+			firstrightstr = BuildIndexValueDescription(rel, values, isnull);
+			index_deform_tuple(newitem, itupdesc, values, isnull);
+			newstr = BuildIndexValueDescription(rel, values, isnull);
+
+			elog(LOG, "\"%s\" leaf block %u "
+				 "last left %s first right %s "
+				 "attributes truncated: %u from %u%s new item %s",
+				 RelationGetRelationName(rel), BufferGetBlockNumber(buf),
+				 lastleftstr, firstrightstr,
+				 IndexRelationGetNumberOfKeyAttributes(rel) - BTreeTupleGetNAtts(lefthikey, rel),
+				 IndexRelationGetNumberOfKeyAttributes(rel),
+				 BTreeTupleGetHeapTID(lefthikey) != NULL ? " (heap TID added back)" : "",
+				 newstr);
+		}
+#endif
 	}
 	else
+	{
 		lefthikey = item;
+#ifdef DEBUG_SPLITS
+		if (IsNormalProcessingMode() && !IsSystemRelation(rel))
+		{
+			TupleDesc	itupdesc = RelationGetDescr(rel);
+			Datum		values[INDEX_MAX_KEYS];
+			bool		isnull[INDEX_MAX_KEYS];
+			char	   *newhighkey;
+			char	   *newstr;
+
+			index_deform_tuple(lefthikey, itupdesc, values, isnull);
+			newhighkey = BuildIndexValueDescription(rel, values, isnull);
+			index_deform_tuple(newitem, itupdesc, values, isnull);
+			newstr = BuildIndexValueDescription(rel, values, isnull);
+
+			elog(LOG, "\"%s\" internal block %u "
+				 "new high key %s "
+				 "attributes truncated: %u from %u%s new item %s",
+				 RelationGetRelationName(rel), BufferGetBlockNumber(buf),
+				 newhighkey,
+				 IndexRelationGetNumberOfKeyAttributes(rel) - BTreeTupleGetNAtts(lefthikey, rel),
+				 IndexRelationGetNumberOfKeyAttributes(rel),
+				 BTreeTupleGetHeapTID(lefthikey) != NULL ? " (heap TID added back)" : "",
+				 newstr);
+		}
+#endif
+	}
 
 	Assert(BTreeTupleGetNAtts(lefthikey, rel) > 0);
 	Assert(BTreeTupleGetNAtts(lefthikey, rel) <=
@@ -1861,6 +1921,11 @@ _bt_findsplitloc(Relation rel,
 
 		if (firstdiff <= perfectfirstdiff)
 		{
+#ifdef DEBUG_SPLITS
+			elog(LOG, "\"%s\" perfect firstdiff %d returned at point %d out of %d",
+				 RelationGetRelationName(rel), perfectfirstdiff, i,
+				 state.nsplits);
+#endif
 			bestfirstdiff = firstdiff;
 			lowsplit = i;
 			break;
@@ -1879,6 +1944,10 @@ _bt_findsplitloc(Relation rel,
 	if (state.splits != splits)
 		pfree(state.splits);
 
+#ifdef DEBUG_SPLITS
+	elog(LOG, "\"%s\" split location %d out of %u",
+		 RelationGetRelationName(rel), finalfirstright, maxoff);
+#endif
 	return finalfirstright;
 }
 
-- 
2.17.1