Postgresql - WAL - pg_waldump

首先我们看一下pg_waldump的帮助信息。

# pg_waldump --help
pg_waldump decodes and displays PostgreSQL write-ahead logs for debugging.
Usage:
  pg_waldump [OPTION]... [STARTSEG [ENDSEG]]
Options:
  -b, --bkp-details      output detailed information about backup blocks    输出相关备份块的信息。
  -e, --end=RECPTR       stop reading at WAL location RECPTR    设置读取的WAL停止点。
  -f, --follow           keep retrying after reaching end of WAL    到达末尾之后，保持每秒轮询是否有新的WAL出现。
  -n, --limit=N          number of records to display    显示总共输出的条数。
  -p, --path=PATH        directory in which to find log segment files or a    目录。
                         directory with a ./pg_wal that contains such files
                         (default: current directory, ./pg_wal, $PGDATA/pg_wal)
  -r, --rmgr=RMGR        only show records generated by resource manager RMGR;    指定资源管理器生成的记录。list用来展示所有资源管理器名称。
                         use --rmgr=list to list valid resource manager names
  -s, --start=RECPTR     start reading at WAL location RECPTR    设置读取的WAL开始点。
  -t, --timeline=TLI     timeline from which to read log records    设置从那个时间开始读取日志。默认为STARTSEG。
                         (default: 1 or the value used in STARTSEG)
  -V, --version          output version information, then exit    版本信息。
  -x, --xid=XID          only show records with transaction ID XID    显示事务ID
  -z, --stats[=record]   show statistics instead of records    显示概括统计信息。而不是每个记录。可以选择针对每个记录生成统计信息，而不是针对每个 资源管理器生成。
                         (optionally, show per-record statistics)
  -?, --help             show this help, then exit

看一下资源管理器列表

# pg_waldump --rmgr=list
XLOG
Transaction
Storage
CLOG
Database
Tablespace
MultiXact
RelMap
Standby
Heap2
Heap
Btree
Hash
Gin
Gist
Sequence
SPGist
BRIN
CommitTs
ReplicationOrigin
Generic
LogicalMessage

看一下执行的命令

# pg_waldump --start=1/304CEEA8 --end=1/304E1E28
rmgr: Heap2       len (rec/tot):     58/    58, tx:          0, lsn: 1/304CEEA8, prev 1/304CEE70, desc: CLEAN remxid 10102, blkref #0: rel 1663/16385/1247 blk 8
rmgr: Storage     len (rec/tot):     42/    42, tx:          0, lsn: 1/304CEEE8, prev 1/304CEEA8, desc: CREATE base/16385/64511
rmgr: Heap        len (rec/tot):    203/   203, tx:      10103, lsn: 1/304CEF18, prev 1/304CEEE8, desc: INSERT off 31, blkref #0: rel 1663/16385/1247 blk 8
rmgr: Btree       len (rec/tot):     64/    64, tx:      10103, lsn: 1/304CEFE8, prev 1/304CEF18, desc: INSERT_LEAF off 38, blkref #0: rel 1663/16385/2703 blk 2
rmgr: Btree       len (rec/tot):     72/    72, tx:      10103, lsn: 1/304CF028, prev 1/304CEFE8, desc: INSERT_LEAF off 33, blkref #0: rel 1663/16385/2704 blk 2

rmgr : 资源名称

lsn: 1/304CEEA8 日志编号

prev 1/304CEE70

desc ： 对日志详细信息的描述

xid 事务id

增删改的日志

DELETE:

rmgr: Heap        len (rec/tot):     59/   227, tx:      10109, lsn: 1/304EE1A0, prev 1/304EE168, desc: DELETE off 1 KEYS_UPDATED , blkref #0: rel 1663/16385/64501 blk 0 FPW
rmgr: Heap        len (rec/tot):     54/    54, tx:      10109, lsn: 1/304EE288, prev 1/304EE1A0, desc: DELETE off 2 KEYS_UPDATED , blkref #0: rel 1663/16385/64501 blk 0
rmgr: Heap        len (rec/tot):     54/    54, tx:      10109, lsn: 1/304EE2C0, prev 1/304EE288, desc: DELETE off 3 KEYS_UPDATED , blkref #0: rel 1663/16385/64501 blk 0
rmgr: Heap        len (rec/tot):     54/    54, tx:      10109, lsn: 1/304EE2F8, prev 1/304EE2C0, desc: DELETE off 4 KEYS_UPDATED , blkref #0: rel 1663/16385/64501 blk 0
rmgr: Transaction len (rec/tot):     34/    34, tx:      10109, lsn: 1/304EE330, prev 1/304EE2F8, desc: COMMIT 2019-01-15 04:06:31.239516 EST
rmgr: Standby     len (rec/tot):     50/    50, tx:          0, lsn: 1/304EE358, prev 1/304EE330, desc: RUNNING_XACTS nextXid 10110 latestCompletedXid 10109 oldestRunningXid 10110

INSERT:

rmgr: Heap        len (rec/tot):     59/    59, tx:      10110, lsn: 1/304EE390, prev 1/304EE358, desc: INSERT off 5, blkref #0: rel 1663/16385/64501 blk 0
rmgr: Transaction len (rec/tot):     34/    34, tx:      10110, lsn: 1/304EE3D0, prev 1/304EE390, desc: COMMIT 2019-01-15 04:07:05.287538 EST
rmgr: Heap        len (rec/tot):     59/    59, tx:      10111, lsn: 1/304EE3F8, prev 1/304EE3D0, desc: INSERT off 6, blkref #0: rel 1663/16385/64501 blk 0
rmgr: Transaction len (rec/tot):     34/    34, tx:      10111, lsn: 1/304EE438, prev 1/304EE3F8, desc: COMMIT 2019-01-15 04:07:09.351770 EST
rmgr: Standby     len (rec/tot):     50/    50, tx:          0, lsn: 1/304EE460, prev 1/304EE438, desc: RUNNING_XACTS nextXid 10112 latestCompletedXid 10111 oldestRunningXid 10112

UPDATE:

rmgr: Heap        len (rec/tot):     69/    69, tx:      10112, lsn: 1/304EE498, prev 1/304EE460, desc: HOT_UPDATE off 5 xmax 10112 ; new off 7 xmax 0, blkref #0: rel 1663/16385/64501 blk 0
rmgr: Transaction len (rec/tot):     34/    34, tx:      10112, lsn: 1/304EE4E0, prev 1/304EE498, desc: COMMIT 2019-01-15 04:07:36.153162 EST
rmgr: Standby     len (rec/tot):     50/    50, tx:          0, lsn: 1/304EE508, prev 1/304EE4E0, desc: RUNNING_XACTS nextXid 10113 latestCompletedXid 10112 oldestRunningXid 10113