Fix nbtree posting list update desc output.

We cannot use the generic array_desc approach with per-tuple nbtree
posting list update metadata because array_desc can only deal with fixed
width elements (e.g., page offset numbers).  Using array_desc led to
incorrect rmgr descriptions for updates from nbtree DELETE/VACUUM WAL
records.

To fix, add specialized code to describe the update metadata as array
elements in desc output.  We now iterate over the update metadata using
an approach that matches related REDO routines.

Also stop showing the updates offset number array separately in nbtree
DELETE/VACUUM desc output.  It's redundant information, since the same
page offset numbers appear in the description of each individual update
element.  Also make some small tweaks to the way that we format arrays
in all desc routines (not just nbtree desc routines) to make arrays a
little less verbose.

Oversight in commit 1c453cfd, which enhanced the nbtree rmgr desc
routines.

Author: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAH2-WzkbYuvwYKm-Y-72QEh6SPMQcAo9uONv+mR3bMGcu9E_Cg@mail.gmail.com

4 files changed, 70 insertions, 81 deletions

diff --git a/src/backend/access/rmgrdesc/heapdesc.c b/src/backend/access/rmgrdesc/heapdesc.c
index 6dfd7d7d130..3bd08387520 100644
--- a/src/backend/access/rmgrdesc/heapdesc.c
+++ b/src/backend/access/rmgrdesc/heapdesc.c
@@ -127,7 +127,7 @@ heap_desc(StringInfo buf, XLogReaderState *record)
 		appendStringInfo(buf, ", nrelids: %u", xlrec->nrelids);
 		appendStringInfoString(buf, ", relids:");
 		array_desc(buf, xlrec->relids, sizeof(Oid), xlrec->nrelids,
-				   &relid_desc, NULL);
+				   &oid_elem_desc, NULL);
 	}
 	else if (info == XLOG_HEAP_CONFIRM)
 	{
diff --git a/src/backend/access/rmgrdesc/nbtdesc.c b/src/backend/access/rmgrdesc/nbtdesc.c
index 6bc0432650f..0db3274dc51 100644
--- a/src/backend/access/rmgrdesc/nbtdesc.c
+++ b/src/backend/access/rmgrdesc/nbtdesc.c
@@ -17,59 +17,8 @@
 #include "access/nbtxlog.h"
 #include "access/rmgrdesc_utils.h"
 
-static void btree_del_desc(StringInfo buf, char *block_data, uint16 ndeleted,
-						   uint16 nupdated);
-static void btree_update_elem_desc(StringInfo buf, void *update, void *data);
-
-static void
-btree_del_desc(StringInfo buf, char *block_data, uint16 ndeleted,
-			   uint16 nupdated)
-{
-	OffsetNumber *updatedoffsets;
-	xl_btree_update *updates;
-	OffsetNumber *data = (OffsetNumber *) block_data;
-
-	appendStringInfoString(buf, ", deleted:");
-	array_desc(buf, data, sizeof(OffsetNumber), ndeleted,
-			   &offset_elem_desc, NULL);
-
-	appendStringInfoString(buf, ", updated:");
-	array_desc(buf, data, sizeof(OffsetNumber), nupdated,
-			   &offset_elem_desc, NULL);
-
-	if (nupdated <= 0)
-		return;
-
-	updatedoffsets = (OffsetNumber *)
-		((char *) data + ndeleted * sizeof(OffsetNumber));
-	updates = (xl_btree_update *) ((char *) updatedoffsets +
-								   nupdated *
-								   sizeof(OffsetNumber));
-
-	appendStringInfoString(buf, ", updates:");
-	array_desc(buf, updates, sizeof(xl_btree_update),
-			   nupdated, &btree_update_elem_desc,
-			   &updatedoffsets);
-}
-
-static void
-btree_update_elem_desc(StringInfo buf, void *update, void *data)
-{
-	xl_btree_update *new_update = (xl_btree_update *) update;
-	OffsetNumber *updated_offset = *((OffsetNumber **) data);
-
-	appendStringInfo(buf, "{ updated offset: %u, ndeleted tids: %u",
-					 *updated_offset, new_update->ndeletedtids);
-
-	appendStringInfoString(buf, ", deleted tids:");
-
-	array_desc(buf, (char *) new_update + SizeOfBtreeUpdate, sizeof(uint16),
-			   new_update->ndeletedtids, &uint16_elem_desc, NULL);
-
-	updated_offset++;
-
-	appendStringInfo(buf, " }");
-}
+static void delvacuum_desc(StringInfo buf, char *block_data,
+						   uint16 ndeleted, uint16 nupdated);
 
 void
 btree_desc(StringInfo buf, XLogReaderState *record)
@@ -114,9 +63,8 @@ btree_desc(StringInfo buf, XLogReaderState *record)
 								 xlrec->ndeleted, xlrec->nupdated);
 
 				if (!XLogRecHasBlockImage(record, 0))
-					btree_del_desc(buf, XLogRecGetBlockData(record, 0, NULL),
+					delvacuum_desc(buf, XLogRecGetBlockData(record, 0, NULL),
 								   xlrec->ndeleted, xlrec->nupdated);
-
 				break;
 			}
 		case XLOG_BTREE_DELETE:
@@ -128,16 +76,15 @@ btree_desc(StringInfo buf, XLogReaderState *record)
 								 xlrec->ndeleted, xlrec->nupdated);
 
 				if (!XLogRecHasBlockImage(record, 0))
-					btree_del_desc(buf, XLogRecGetBlockData(record, 0, NULL),
+					delvacuum_desc(buf, XLogRecGetBlockData(record, 0, NULL),
 								   xlrec->ndeleted, xlrec->nupdated);
-
 				break;
 			}
 		case XLOG_BTREE_MARK_PAGE_HALFDEAD:
 			{
 				xl_btree_mark_page_halfdead *xlrec = (xl_btree_mark_page_halfdead *) rec;
 
-				appendStringInfo(buf, "topparent: %u; leaf: %u; left: %u; right: %u",
+				appendStringInfo(buf, "topparent: %u, leaf: %u, left: %u, right: %u",
 								 xlrec->topparent, xlrec->leafblk, xlrec->leftblk, xlrec->rightblk);
 				break;
 			}
@@ -146,11 +93,11 @@ btree_desc(StringInfo buf, XLogReaderState *record)
 			{
 				xl_btree_unlink_page *xlrec = (xl_btree_unlink_page *) rec;
 
-				appendStringInfo(buf, "left: %u; right: %u; level: %u; safexid: %u:%u; ",
+				appendStringInfo(buf, "left: %u, right: %u, level: %u, safexid: %u:%u, ",
 								 xlrec->leftsib, xlrec->rightsib, xlrec->level,
 								 EpochFromFullTransactionId(xlrec->safexid),
 								 XidFromFullTransactionId(xlrec->safexid));
-				appendStringInfo(buf, "leafleft: %u; leafright: %u; leaftopparent: %u",
+				appendStringInfo(buf, "leafleft: %u, leafright: %u, leaftopparent: %u",
 								 xlrec->leafleftsib, xlrec->leafrightsib,
 								 xlrec->leaftopparent);
 				break;
@@ -242,3 +189,59 @@ btree_identify(uint8 info)
 
 	return id;
 }
+
+static void
+delvacuum_desc(StringInfo buf, char *block_data,
+			   uint16 ndeleted, uint16 nupdated)
+{
+	OffsetNumber *deletedoffsets;
+	OffsetNumber *updatedoffsets;
+	xl_btree_update *updates;
+
+	/* Output deleted page offset number array */
+	appendStringInfoString(buf, ", deleted:");
+	deletedoffsets = (OffsetNumber *) block_data;
+	array_desc(buf, deletedoffsets, sizeof(OffsetNumber), ndeleted,
+			   &offset_elem_desc, NULL);
+
+	/*
+	 * Output updates as an array of "update objects", where each element
+	 * contains a page offset number from updated array.  (This is not the
+	 * most literal representation of the underlying physical data structure
+	 * that we could use.  Readability seems more important here.)
+	 */
+	appendStringInfoString(buf, ", updated: [");
+	updatedoffsets = (OffsetNumber *) (block_data + ndeleted *
+									   sizeof(OffsetNumber));
+	updates = (xl_btree_update *) ((char *) updatedoffsets +
+								   nupdated *
+								   sizeof(OffsetNumber));
+	for (int i = 0; i < nupdated; i++)
+	{
+		OffsetNumber off = updatedoffsets[i];
+
+		Assert(OffsetNumberIsValid(off));
+		Assert(updates->ndeletedtids > 0);
+
+		appendStringInfo(buf, "{ off: %u, nptids: %u, ptids: [",
+						 off, updates->ndeletedtids);
+		for (int p = 0; p < updates->ndeletedtids; p++)
+		{
+			uint16	   *ptid;
+
+			ptid = (uint16 *) ((char *) updates + SizeOfBtreeUpdate) + p;
+			appendStringInfo(buf, "%u", *ptid);
+
+			if (p < updates->ndeletedtids - 1)
+				appendStringInfoString(buf, ", ");
+		}
+		appendStringInfoString(buf, "] }");
+		if (i < nupdated - 1)
+			appendStringInfoString(buf, ", ");
+
+		updates = (xl_btree_update *)
+			((char *) updates + SizeOfBtreeUpdate +
+			 updates->ndeletedtids * sizeof(uint16));
+	}
+	appendStringInfoString(buf, "]");
+}
diff --git a/src/backend/access/rmgrdesc/rmgrdesc_utils.c b/src/backend/access/rmgrdesc/rmgrdesc_utils.c
index c95a41a254b..3d16b1fcba3 100644
--- a/src/backend/access/rmgrdesc/rmgrdesc_utils.c
+++ b/src/backend/access/rmgrdesc/rmgrdesc_utils.c
@@ -29,16 +29,11 @@
  * or comma, however all subsequent appends to the string are responsible for
  * prepending themselves with a comma followed by a space.
  *
- * Arrays should have a space between the opening square bracket and first
- * element and between the last element and closing brace.
- *
  * Flags should be in ALL CAPS.
  *
  * For lists/arrays of items, the number of those items should be listed at
  * the beginning with all of the other numbers.
  *
- * List punctuation should still be included even if there are 0 items.
- *
  * Composite objects in a list should be surrounded with { }.
  */
 void
@@ -51,16 +46,14 @@ array_desc(StringInfo buf, void *array, size_t elem_size, int count,
 		appendStringInfoString(buf, " []");
 		return;
 	}
-	appendStringInfo(buf, " [");
+	appendStringInfoString(buf, " [");
 	for (int i = 0; i < count; i++)
 	{
-		if (i > 0)
-			appendStringInfoString(buf, ",");
-		appendStringInfoString(buf, " ");
-
 		elem_desc(buf, (char *) array + elem_size * i, data);
+		if (i < count - 1)
+			appendStringInfoString(buf, ", ");
 	}
-	appendStringInfoString(buf, " ]");
+	appendStringInfoString(buf, "]");
 }
 
 void
@@ -78,13 +71,7 @@ redirect_elem_desc(StringInfo buf, void *offset, void *data)
 }
 
 void
-relid_desc(StringInfo buf, void *relid, void *data)
+oid_elem_desc(StringInfo buf, void *relid, void *data)
 {
 	appendStringInfo(buf, "%u", *(Oid *) relid);
 }
-
-void
-uint16_elem_desc(StringInfo buf, void *value, void *data)
-{
-	appendStringInfo(buf, "%u", *(uint16 *) value);
-}
diff --git a/src/include/access/rmgrdesc_utils.h b/src/include/access/rmgrdesc_utils.h
index 13552d6f350..00e61464906 100644
--- a/src/include/access/rmgrdesc_utils.h
+++ b/src/include/access/rmgrdesc_utils.h
@@ -17,7 +17,6 @@ extern void array_desc(StringInfo buf, void *array, size_t elem_size, int count,
 					   void *data);
 extern void offset_elem_desc(StringInfo buf, void *offset, void *data);
 extern void redirect_elem_desc(StringInfo buf, void *offset, void *data);
-extern void relid_desc(StringInfo buf, void *relid, void *data);
-extern void uint16_elem_desc(StringInfo buf, void *value, void *data);
+extern void oid_elem_desc(StringInfo buf, void *relid, void *data);
 
 #endif							/* RMGRDESC_UTILS_H */