Fix pageinspect failures on hash indexes.

Make every page in a hash index which isn't all-zeroes have a valid
special space, so that tools like pageinspect don't error out.

Also, make pageinspect cope with all-zeroes pages, because
_hash_alloc_buckets can leave behind large numbers of those until
they're consumed by splits.

Ashutosh Sharma and Robert Haas, reviewed by Amit Kapila.
Original trouble report from Jeff Janes.

Discussion: http://postgr.es/m/CAMkU=1y6NjKmqbJ8wLMhr=F74WzcMALYWcVFhEpm7i=mV=XsOg@mail.gmail.com

3 files changed, 34 insertions, 4 deletions

diff --git a/src/backend/access/hash/hash_xlog.c b/src/backend/access/hash/hash_xlog.c
index d9ac42c394..2ccaf469e7 100644
--- a/src/backend/access/hash/hash_xlog.c
+++ b/src/backend/access/hash/hash_xlog.c
@@ -697,11 +697,20 @@ hash_xlog_squeeze_page(XLogReaderState *record)
 	if (XLogReadBufferForRedo(record, 2, &ovflbuf) == BLK_NEEDS_REDO)
 	{
 		Page		ovflpage;
+		HashPageOpaque ovflopaque;
 
 		ovflpage = BufferGetPage(ovflbuf);
 
 		_hash_pageinit(ovflpage, BufferGetPageSize(ovflbuf));
 
+		ovflopaque = (HashPageOpaque) PageGetSpecialPointer(ovflpage);
+
+		ovflopaque->hasho_prevblkno = InvalidBlockNumber;
+		ovflopaque->hasho_nextblkno = InvalidBlockNumber;
+		ovflopaque->hasho_bucket = -1;
+		ovflopaque->hasho_flag = LH_UNUSED_PAGE;
+		ovflopaque->hasho_page_id = HASHO_PAGE_ID;
+
 		PageSetLSN(ovflpage, lsn);
 		MarkBufferDirty(ovflbuf);
 	}
diff --git a/src/backend/access/hash/hashovfl.c b/src/backend/access/hash/hashovfl.c
index 41ef654862..d5f5023068 100644
--- a/src/backend/access/hash/hashovfl.c
+++ b/src/backend/access/hash/hashovfl.c
@@ -590,11 +590,22 @@ _hash_freeovflpage(Relation rel, Buffer bucketbuf, Buffer ovflbuf,
 	}
 
 	/*
-	 * Initialize the freed overflow page.  Just zeroing the page won't work,
-	 * because WAL replay routines expect pages to be initialized. See
-	 * explanation of RBM_NORMAL mode atop XLogReadBufferExtended.
+	 * Reinitialize the freed overflow page.  Just zeroing the page won't
+	 * work, because WAL replay routines expect pages to be initialized. See
+	 * explanation of RBM_NORMAL mode atop XLogReadBufferExtended.  We are
+	 * careful to make the special space valid here so that tools like
+	 * pageinspect won't get confused.
 	 */
 	_hash_pageinit(ovflpage, BufferGetPageSize(ovflbuf));
+
+	ovflopaque = (HashPageOpaque) PageGetSpecialPointer(ovflpage);
+
+	ovflopaque->hasho_prevblkno = InvalidBlockNumber;
+	ovflopaque->hasho_nextblkno = InvalidBlockNumber;
+	ovflopaque->hasho_bucket = -1;
+	ovflopaque->hasho_flag = LH_UNUSED_PAGE;
+	ovflopaque->hasho_page_id = HASHO_PAGE_ID;
+
 	MarkBufferDirty(ovflbuf);
 
 	if (BufferIsValid(prevbuf))
diff --git a/src/backend/access/hash/hashpage.c b/src/backend/access/hash/hashpage.c
index b5a1c7ed28..3cd4daa325 100644
--- a/src/backend/access/hash/hashpage.c
+++ b/src/backend/access/hash/hashpage.c
@@ -993,6 +993,7 @@ _hash_alloc_buckets(Relation rel, BlockNumber firstblock, uint32 nblocks)
 	BlockNumber lastblock;
 	char		zerobuf[BLCKSZ];
 	Page		page;
+	HashPageOpaque ovflopaque;
 
 	lastblock = firstblock + nblocks - 1;
 
@@ -1007,10 +1008,19 @@ _hash_alloc_buckets(Relation rel, BlockNumber firstblock, uint32 nblocks)
 
 	/*
 	 * Initialize the page.  Just zeroing the page won't work; see
-	 * _hash_freeovflpage for similar usage.
+	 * _hash_freeovflpage for similar usage.  We take care to make the
+	 * special space valid for the benefit of tools such as pageinspect.
 	 */
 	_hash_pageinit(page, BLCKSZ);
 
+	ovflopaque = (HashPageOpaque) PageGetSpecialPointer(page);
+
+	ovflopaque->hasho_prevblkno = InvalidBlockNumber;
+	ovflopaque->hasho_nextblkno = InvalidBlockNumber;
+	ovflopaque->hasho_bucket = -1;
+	ovflopaque->hasho_flag = LH_UNUSED_PAGE;
+	ovflopaque->hasho_page_id = HASHO_PAGE_ID;
+
 	if (RelationNeedsWAL(rel))
 		log_newpage(&rel->rd_node,
 					MAIN_FORKNUM,