*
* Definitions for the WAL record format.
*
- * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/access/xlogrecord.h
#include "access/rmgr.h"
#include "access/xlogdefs.h"
-#include "common/pg_crc.h"
+#include "port/pg_crc32c.h"
#include "storage/block.h"
#include "storage/relfilenode.h"
uint8 xl_info; /* flag bits, see below */
RmgrId xl_rmid; /* resource manager for this record */
/* 2 bytes of padding here, initialize to zero */
- pg_crc32 xl_crc; /* CRC for this record */
+ pg_crc32c xl_crc; /* CRC for this record */
/* XLogRecordBlockHeaders and XLogRecordDataHeader follow, no padding */
} XLogRecord;
-#define SizeOfXLogRecord (offsetof(XLogRecord, xl_crc) + sizeof(pg_crc32))
+#define SizeOfXLogRecord (offsetof(XLogRecord, xl_crc) + sizeof(pg_crc32c))
/*
* The high 4 bits in xl_info may be used freely by rmgr. The
*
* As a trivial form of data compression, the XLOG code is aware that
* PG data pages usually contain an unused "hole" in the middle, which
- * contains only zero bytes. If hole_length > 0 then we have removed
+ * contains only zero bytes. If the length of "hole" > 0 then we have removed
* such a "hole" from the stored data (and it's not counted in the
* XLOG record's CRC, either). Hence, the amount of block data actually
- * present is BLCKSZ - hole_length bytes.
+ * present is BLCKSZ - the length of "hole" bytes.
+ *
+ * When wal_compression is enabled, a full page image which "hole" was
+ * removed is additionally compressed using PGLZ compression algorithm.
+ * This can reduce the WAL volume, but at some extra cost of CPU spent
+ * on the compression during WAL logging. In this case, since the "hole"
+ * length cannot be calculated by subtracting the number of page image bytes
+ * from BLCKSZ, basically it needs to be stored as an extra information.
+ * But when no "hole" exists, we can assume that the "hole" length is zero
+ * and no such an extra information needs to be stored. Note that
+ * the original version of page image is stored in WAL instead of the
+ * compressed one if the number of bytes saved by compression is less than
+ * the length of extra information. Hence, when a page image is successfully
+ * compressed, the amount of block data actually present is less than
+ * BLCKSZ - the length of "hole" bytes - the length of extra information.
*/
typedef struct XLogRecordBlockImageHeader
{
+ uint16 length; /* number of page image bytes */
uint16 hole_offset; /* number of bytes before "hole" */
- uint16 hole_length; /* number of bytes in "hole" */
+ uint8 bimg_info; /* flag bits, see below */
+
+ /*
+ * If BKPIMAGE_HAS_HOLE and BKPIMAGE_IS_COMPRESSED, an
+ * XLogRecordBlockCompressHeader struct follows.
+ */
} XLogRecordBlockImageHeader;
-#define SizeOfXLogRecordBlockImageHeader sizeof(XLogRecordBlockImageHeader)
+#define SizeOfXLogRecordBlockImageHeader \
+ (offsetof(XLogRecordBlockImageHeader, bimg_info) + sizeof(uint8))
+
+/* Information stored in bimg_info */
+#define BKPIMAGE_HAS_HOLE 0x01 /* page image has "hole" */
+#define BKPIMAGE_IS_COMPRESSED 0x02 /* page image is compressed */
+
+/*
+ * Extra header information used when page image has "hole" and
+ * is compressed.
+ */
+typedef struct XLogRecordBlockCompressHeader
+{
+ uint16 hole_length; /* number of bytes in "hole" */
+} XLogRecordBlockCompressHeader;
+
+#define SizeOfXLogRecordBlockCompressHeader \
+ sizeof(XLogRecordBlockCompressHeader)
/*
* Maximum size of the header for a block reference. This is used to size a
#define MaxSizeOfXLogRecordBlockHeader \
(SizeOfXLogRecordBlockHeader + \
SizeOfXLogRecordBlockImageHeader + \
+ SizeOfXLogRecordBlockCompressHeader + \
sizeof(RelFileNode) + \
sizeof(BlockNumber))
{
uint8 id; /* XLR_BLOCK_ID_DATA_SHORT */
uint8 data_length; /* number of payload bytes */
-} XLogRecordDataHeaderShort;
+} XLogRecordDataHeaderShort;
#define SizeOfXLogRecordDataHeaderShort (sizeof(uint8) * 2)
{
uint8 id; /* XLR_BLOCK_ID_DATA_LONG */
/* followed by uint32 data_length, unaligned */
-} XLogRecordDataHeaderLong;
+} XLogRecordDataHeaderLong;
#define SizeOfXLogRecordDataHeaderLong (sizeof(uint8) + sizeof(uint32))
#define XLR_BLOCK_ID_DATA_SHORT 255
#define XLR_BLOCK_ID_DATA_LONG 254
+#define XLR_BLOCK_ID_ORIGIN 253
#endif /* XLOGRECORD_H */