hash: Add write-ahead logging support.

The warning about hash indexes not being write-ahead logged and their
use being discouraged has been removed.  "snapshot too old" is now
supported for tables with hash indexes.  Most importantly, barring
bugs, hash indexes will now be crash-safe and usable on standbys.

This commit doesn't yet add WAL consistency checking for hash
indexes, as we now have for other index types; a separate patch has
been submitted to cure that lack.

Amit Kapila, reviewed and slightly modified by me.  The larger patch
series of which this is a part has been reviewed and tested by Álvaro
Herrera, Ashutosh Sharma, Mark Kirkwood, Jeff Janes, and Jesper
Pedersen.

Discussion: http://postgr.es/m/CAA4eK1JOBX=YU33631Qh-XivYXtPSALh514+jR8XeD7v+K3r_Q@mail.gmail.com

src/include/access/hash_xlog.h

@@ -16,7 +16,239 @@
 
 #include "access/xlogreader.h"
 #include "lib/stringinfo.h"
+#include "storage/off.h"
 
+/* Number of buffers required for XLOG_HASH_SQUEEZE_PAGE operation */
+#define HASH_XLOG_FREE_OVFL_BUFS	6
+
+/*
+ * XLOG records for hash operations
+ */
+#define XLOG_HASH_INIT_META_PAGE	0x00		/* initialize the meta page */
+#define XLOG_HASH_INIT_BITMAP_PAGE	0x10		/* initialize the bitmap page */
+#define XLOG_HASH_INSERT		0x20	/* add index tuple without split */
+#define XLOG_HASH_ADD_OVFL_PAGE 0x30	/* add overflow page */
+#define XLOG_HASH_SPLIT_ALLOCATE_PAGE	0x40	/* allocate new page for split */
+#define XLOG_HASH_SPLIT_PAGE	0x50	/* split page */
+#define XLOG_HASH_SPLIT_COMPLETE	0x60		/* completion of split
+												 * operation */
+#define XLOG_HASH_MOVE_PAGE_CONTENTS	0x70	/* remove tuples from one page
+												 * and add to another page */
+#define XLOG_HASH_SQUEEZE_PAGE	0x80	/* add tuples to one of the previous
+										 * pages in chain and free the ovfl
+										 * page */
+#define XLOG_HASH_DELETE		0x90	/* delete index tuples from a page */
+#define XLOG_HASH_SPLIT_CLEANUP 0xA0	/* clear split-cleanup flag in primary
+										 * bucket page after deleting tuples
+										 * that are moved due to split	*/
+#define XLOG_HASH_UPDATE_META_PAGE	0xB0		/* update meta page after
+												 * vacuum */
+
+
+/*
+ * xl_hash_split_allocate_page flag values, 8 bits are available.
+ */
+#define XLH_SPLIT_META_UPDATE_MASKS		(1<<0)
+#define XLH_SPLIT_META_UPDATE_SPLITPOINT		(1<<1)
+
+/*
+ * This is what we need to know about a HASH index create.
+ *
+ * Backup block 0: metapage
+ */
+typedef struct xl_hash_createidx
+{
+	double		num_tuples;
+	RegProcedure procid;
+	uint16		ffactor;
+}	xl_hash_createidx;
+#define SizeOfHashCreateIdx (offsetof(xl_hash_createidx, ffactor) + sizeof(uint16))
+
+/*
+ * This is what we need to know about simple (without split) insert.
+ *
+ * This data record is used for XLOG_HASH_INSERT
+ *
+ * Backup Blk 0: original page (data contains the inserted tuple)
+ * Backup Blk 1: metapage (HashMetaPageData)
+ */
+typedef struct xl_hash_insert
+{
+	OffsetNumber offnum;
+}	xl_hash_insert;
+
+#define SizeOfHashInsert	(offsetof(xl_hash_insert, offnum) + sizeof(OffsetNumber))
+
+/*
+ * This is what we need to know about addition of overflow page.
+ *
+ * This data record is used for XLOG_HASH_ADD_OVFL_PAGE
+ *
+ * Backup Blk 0: newly allocated overflow page
+ * Backup Blk 1: page before new overflow page in the bucket chain
+ * Backup Blk 2: bitmap page
+ * Backup Blk 3: new bitmap page
+ * Backup Blk 4: metapage
+ */
+typedef struct xl_hash_add_ovfl_page
+{
+	uint16		bmsize;
+	bool		bmpage_found;
+}	xl_hash_add_ovfl_page;
+
+#define SizeOfHashAddOvflPage	\
+	(offsetof(xl_hash_add_ovfl_page, bmpage_found) + sizeof(bool))
+
+/*
+ * This is what we need to know about allocating a page for split.
+ *
+ * This data record is used for XLOG_HASH_SPLIT_ALLOCATE_PAGE
+ *
+ * Backup Blk 0: page for old bucket
+ * Backup Blk 1: page for new bucket
+ * Backup Blk 2: metapage
+ */
+typedef struct xl_hash_split_allocate_page
+{
+	uint32		new_bucket;
+	uint16		old_bucket_flag;
+	uint16		new_bucket_flag;
+	uint8		flags;
+}	xl_hash_split_allocate_page;
+
+#define SizeOfHashSplitAllocPage	\
+	(offsetof(xl_hash_split_allocate_page, flags) + sizeof(uint8))
+
+/*
+ * This is what we need to know about completing the split operation.
+ *
+ * This data record is used for XLOG_HASH_SPLIT_COMPLETE
+ *
+ * Backup Blk 0: page for old bucket
+ * Backup Blk 1: page for new bucket
+ */
+typedef struct xl_hash_split_complete
+{
+	uint16		old_bucket_flag;
+	uint16		new_bucket_flag;
+}	xl_hash_split_complete;
+
+#define SizeOfHashSplitComplete \
+	(offsetof(xl_hash_split_complete, new_bucket_flag) + sizeof(uint16))
+
+/*
+ * This is what we need to know about move page contents required during
+ * squeeze operation.
+ *
+ * This data record is used for XLOG_HASH_MOVE_PAGE_CONTENTS
+ *
+ * Backup Blk 0: bucket page
+ * Backup Blk 1: page containing moved tuples
+ * Backup Blk 2: page from which tuples will be removed
+ */
+typedef struct xl_hash_move_page_contents
+{
+	uint16		ntups;
+	bool		is_prim_bucket_same_wrt;		/* TRUE if the page to which
+												 * tuples are moved is same as
+												 * primary bucket page */
+}	xl_hash_move_page_contents;
+
+#define SizeOfHashMovePageContents	\
+	(offsetof(xl_hash_move_page_contents, is_prim_bucket_same_wrt) + sizeof(bool))
+
+/*
+ * This is what we need to know about the squeeze page operation.
+ *
+ * This data record is used for XLOG_HASH_SQUEEZE_PAGE
+ *
+ * Backup Blk 0: page containing tuples moved from freed overflow page
+ * Backup Blk 1: freed overflow page
+ * Backup Blk 2: page previous to the freed overflow page
+ * Backup Blk 3: page next to the freed overflow page
+ * Backup Blk 4: bitmap page containing info of freed overflow page
+ * Backup Blk 5: meta page
+ */
+typedef struct xl_hash_squeeze_page
+{
+	BlockNumber prevblkno;
+	BlockNumber nextblkno;
+	uint16		ntups;
+	bool		is_prim_bucket_same_wrt;		/* TRUE if the page to which
+												 * tuples are moved is same as
+												 * primary bucket page */
+	bool		is_prev_bucket_same_wrt;		/* TRUE if the page to which
+												 * tuples are moved is the
+												 * page previous to the freed
+												 * overflow page */
+}	xl_hash_squeeze_page;
+
+#define SizeOfHashSqueezePage	\
+	(offsetof(xl_hash_squeeze_page, is_prev_bucket_same_wrt) + sizeof(bool))
+
+/*
+ * This is what we need to know about the deletion of index tuples from a page.
+ *
+ * This data record is used for XLOG_HASH_DELETE
+ *
+ * Backup Blk 0: primary bucket page
+ * Backup Blk 1: page from which tuples are deleted
+ */
+typedef struct xl_hash_delete
+{
+	bool		is_primary_bucket_page; /* TRUE if the operation is for
+										 * primary bucket page */
+}	xl_hash_delete;
+
+#define SizeOfHashDelete	(offsetof(xl_hash_delete, is_primary_bucket_page) + sizeof(bool))
+
+/*
+ * This is what we need for metapage update operation.
+ *
+ * This data record is used for XLOG_HASH_UPDATE_META_PAGE
+ *
+ * Backup Blk 0: meta page
+ */
+typedef struct xl_hash_update_meta_page
+{
+	double		ntuples;
+}	xl_hash_update_meta_page;
+
+#define SizeOfHashUpdateMetaPage	\
+	(offsetof(xl_hash_update_meta_page, ntuples) + sizeof(double))
+
+/*
+ * This is what we need to initialize metapage.
+ *
+ * This data record is used for XLOG_HASH_INIT_META_PAGE
+ *
+ * Backup Blk 0: meta page
+ */
+typedef struct xl_hash_init_meta_page
+{
+	double		num_tuples;
+	RegProcedure procid;
+	uint16		ffactor;
+}	xl_hash_init_meta_page;
+
+#define SizeOfHashInitMetaPage		\
+	(offsetof(xl_hash_init_meta_page, ffactor) + sizeof(uint16))
+
+/*
+ * This is what we need to initialize bitmap page.
+ *
+ * This data record is used for XLOG_HASH_INIT_BITMAP_PAGE
+ *
+ * Backup Blk 0: bitmap page
+ * Backup Blk 1: meta page
+ */
+typedef struct xl_hash_init_bitmap_page
+{
+	uint16		bmsize;
+}	xl_hash_init_bitmap_page;
+
+#define SizeOfHashInitBitmapPage	\
+	(offsetof(xl_hash_init_bitmap_page, bmsize) + sizeof(uint16))
 
 extern void hash_redo(XLogReaderState *record);
 extern void hash_desc(StringInfo buf, XLogReaderState *record);