Postgresql源码（7）Xlog格式

typedef struct XLogPageHeaderData
{
【校验用magic数字】
	uint16		xlp_magic;		/* magic value for correctness checks */
【标志位信息】
	uint16		xlp_info;		/* flag bits, see below */
【时间线信息】
	TimeLineID	xlp_tli;		/* TimeLineID of first record on page */
【当前页面在日志文件中的位置】
	XLogRecPtr	xlp_pageaddr;	/* XLOG address of this page */
【日志跨页面保存，当前页面需要存的剩下的长度】
	uint32		xlp_rem_len;	/* total len of remaining data for record */
} XLogPageHeaderData;

typedef struct XLogRecord
{
【日记长度】
	uint32		xl_tot_len;		/* total len of entire record */
【事务ID】
	TransactionId xl_xid;		/* xact id */
【上一条日志的LSN】
	XLogRecPtr	xl_prev;		/* ptr to previous record in log */
【产生这个记录的动作】
	uint8		xl_info;		/* flag bits, see below */
【日志记录对应的资源管理器】
	RmgrId		xl_rmid;		/* resource manager for this record */
	/* 2 bytes of padding here, initialize to zero */
	pg_crc32c	xl_crc;			/* CRC for this record */

	/* XLogRecordBlockHeaders and XLogRecordDataHeader follow, no padding */
【日志的数据信息】
} XLogRecord;

/*
 * If a WAL record modifies any relation files, in ways not covered by the
 * usual block references, this flag is set. This is not used for anything
 * by PostgreSQL itself, but it allows external tools that read WAL and keep
 * track of modified blocks to recognize such special record types.
 */
#define XLR_SPECIAL_REL_UPDATE	0x01

/*
 * Enforces consistency checks of replayed WAL at recovery. If enabled,
 * each record will log a full-page write for each block modified by the
 * record and will reuse it afterwards for consistency checks. The caller
 * of XLogInsert can use this value if necessary, but if
 * wal_consistency_checking is enabled for a rmgr this is set unconditionally.
 */
#define XLR_CHECK_CONSISTENCY	0x02

#define XLOG_HEAP_INSERT		0x00
#define XLOG_HEAP_DELETE		0x10
#define XLOG_HEAP_UPDATE		0x20
#define XLOG_HEAP_TRUNCATE		0x30
#define XLOG_HEAP_HOT_UPDATE	0x40
#define XLOG_HEAP_CONFIRM		0x50
#define XLOG_HEAP_LOCK			0x60
#define XLOG_HEAP_INPLACE		0x70

#define XLOG_HEAP_OPMASK		0x70
/*
 * When we insert 1st item on new page in INSERT, UPDATE, HOT_UPDATE,
 * or MULTI_INSERT, we can (and we do) restore entire page in redo
 */
#define XLOG_HEAP_INIT_PAGE		0x80

typedef struct XLogRecordDataHeaderShort
{
	uint8		id;				/* XLR_BLOCK_ID_DATA_SHORT */
	uint8		data_length;	/* number of payload bytes */
}			XLogRecordDataHeaderShort;

#define SizeOfXLogRecordDataHeaderShort (sizeof(uint8) * 2)

typedef struct XLogRecordDataHeaderLong
{
	uint8		id;				/* XLR_BLOCK_ID_DATA_LONG */
	/* followed by uint32 data_length, unaligned */
}			XLogRecordDataHeaderLong;

#define SizeOfXLogRecordDataHeaderLong (sizeof(uint8) + sizeof(uint32))