pg_waldump pg_xlogdump 的初步使用

os: centos 7.4
postgresql: 10.4

pg_waldump 是 postgres 10.x 之后的命令，对应之前版本的 pg_xlogdump。
postgresql 从 10 版本开始，将所用xlog相关的全部用wal替换了，同时大版本的命名规则也做了调整。

实际工作总用户难免会误操作，当寻求用户误操作时间时，基本只能得到一个大概的时间范围。
但是通过pg_waldump可以定位到具体的xid或者lsn，然后使用recovery.conf 设置 recovery_target_inclusive = false 进行pitr异机恢复。
具体如下：

# vi recovery.conf
standby_mode = on
restore_command = 'cp /mnt/walbackup/%f %p'
recovery_target_inclusive = false
#大概恢复
#recovery_target_time = '2017-12-21 10:00:00 +08'   
#精确恢复
recovery_target_xid = '1485020'
pause_at_recovery_target = true

pg_waldump –help

$ 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
  -e, --end=RECPTR       stop reading at WAL location RECPTR
  -f, --follow           keep retrying after reaching end of WAL
  -n, --limit=N          number of records to display
  -p, --path=PATH        directory in which to find log segment files or a
                         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;
                         use --rmgr=list to list valid resource manager names
  -s, --start=RECPTR     start reading at WAL location RECPTR
  -t, --timeline=TLI     timeline from which to read log records
                         (default: 1 or the value used in STARTSEG)
  -V, --version          output version information, then exit
  -x, --xid=XID          only show records with transaction ID XID
  -z, --stats[=record]   show statistics instead of records
                         (optionally, show per-record statistics)
  -?, --help             show this help, then exit

分析

 select pg_current_wal_lsn(),
        pg_walfile_name(pg_current_wal_lsn()),
        pg_walfile_name_offset(pg_current_wal_lsn());

 pg_current_wal_lsn |     pg_walfile_name      |       pg_walfile_name_offset       
--------------------+--------------------------+------------------------------------
 0/16A9330          | 000000010000000000000001 | (000000010000000000000001,6984496)
(1 row)

postgres=# create database peiybdb;

postgres=# create table tmp_t0(c1 varchar(100),c2 varchar(100));

postgres=# insert into tmp_t0(c1,c2) values('123','456');

select pg_current_wal_lsn(),
           pg_walfile_name(pg_current_wal_lsn()),
           pg_walfile_name_offset(pg_current_wal_lsn());
 pg_current_wal_lsn |     pg_walfile_name      |       pg_walfile_name_offset       
--------------------+--------------------------+------------------------------------
 0/16C16D8          | 000000010000000000000001 | (000000010000000000000001,7083736)
(1 row)

使用pg_waldump观察输出

$ pg_waldump -s 0/16A9330   $PGDATA/pg_wal/000000010000000000000001

挑选了一些关键信息如下

rmgr: Database    len (rec/tot):     42/    42, tx:        559, lsn: 0/016A9B50, prev 0/016A9AE0, desc: CREATE copy dir 1/1663 to 16388/1663

rmgr: Storage     len (rec/tot):     42/    42, tx:          0, lsn: 0/016A9CA8, prev 0/016A9C70, desc: CREATE base/13806/16389

rmgr: Heap        len (rec/tot):     63/    63, tx:        561, lsn: 0/016C1638, prev 0/016C1600, desc: INSERT+INIT off 1, blkref #0: rel 1663/13806/16389 blk 0
rmgr: Transaction len (rec/tot):     34/    34, tx:        561, lsn: 0/016C1678, prev 0/016C1638, desc: COMMIT 2018-06-10 10:46:52.926390 CST
rmgr: Standby     len (rec/tot):     50/    50, tx:          0, lsn: 0/016C16A0, prev 0/016C1678, desc: RUNNING_XACTS nextXid 562 latestCompletedXid 561 oldestRunningXid 562

再次插入一行

 select pg_current_wal_lsn(),
        pg_walfile_name(pg_current_wal_lsn()),
        pg_walfile_name_offset(pg_current_wal_lsn());
 pg_current_wal_lsn |     pg_walfile_name      |       pg_walfile_name_offset       
--------------------+--------------------------+------------------------------------
 0/16C17B8          | 000000010000000000000001 | (000000010000000000000001,7083960)
(1 row)

insert into tmp_t0(c1,c2) values('111','222');

 select pg_current_wal_lsn(),
        pg_walfile_name(pg_current_wal_lsn()),
        pg_walfile_name_offset(pg_current_wal_lsn());
 pg_current_wal_lsn |     pg_walfile_name      |       pg_walfile_name_offset       
--------------------+--------------------------+------------------------------------
 0/16C1878          | 000000010000000000000001 | (000000010000000000000001,7084152)
(1 row)

再次 pg_waldump

$ pg_waldump -s 0/16C17B8   $PGDATA/pg_wal/000000010000000000000001

挑选了一些关键信息如下

rmgr: Heap        len (rec/tot):     54/   150, tx:        562, lsn: 0/016C17B8, prev 0/016C1780, desc: INSERT off 2, blkref #0: rel 1663/13806/16389 blk 0 FPW
rmgr: Transaction len (rec/tot):     34/    34, tx:        562, lsn: 0/016C1850, prev 0/016C17B8, desc: COMMIT 2018-06-10 10:54:03.267369 CST
rmgr: Standby     len (rec/tot):     50/    50, tx:          0, lsn: 0/016C1878, prev 0/016C1850, desc: RUNNING_XACTS nextXid 563 latestCompletedXid 562 oldestRunningXid 563

插入两行

 select pg_current_wal_lsn(),
        pg_walfile_name(pg_current_wal_lsn()),
        pg_walfile_name_offset(pg_current_wal_lsn());

 pg_current_wal_lsn |     pg_walfile_name      |       pg_walfile_name_offset       
--------------------+--------------------------+------------------------------------
 0/16C1AB8          | 000000010000000000000001 | (000000010000000000000001,7084728)
(1 row)

insert into tmp_t0(c1,c2) values('111','222'),('112','333');

 select pg_current_wal_lsn(),
        pg_walfile_name(pg_current_wal_lsn()),
        pg_walfile_name_offset(pg_current_wal_lsn());
pg_current_wal_lsn |     pg_walfile_name      |       pg_walfile_name_offset       
--------------------+--------------------------+------------------------------------
 0/16C1BD0          | 000000010000000000000001 | (000000010000000000000001,7085008)
(1 row)

$ pg_waldump -s 0/16C1AB8   $PGDATA/pg_wal/000000010000000000000001

rmgr: Standby     len (rec/tot):     50/    50, tx:          0, lsn: 0/016C1AB8, prev 0/016C1A90, desc: RUNNING_XACTS nextXid 564 latestCompletedXid 563 oldestRunningXid 564
rmgr: Heap        len (rec/tot):     63/    63, tx:        564, lsn: 0/016C1AF0, prev 0/016C1AB8, desc: INSERT off 5, blkref #0: rel 1663/13806/16389 blk 0
rmgr: Heap        len (rec/tot):     63/    63, tx:        564, lsn: 0/016C1B30, prev 0/016C1AF0, desc: INSERT off 6, blkref #0: rel 1663/13806/16389 blk 0
rmgr: Transaction len (rec/tot):     34/    34, tx:        564, lsn: 0/016C1B70, prev 0/016C1B30, desc: COMMIT 2018-06-10 10:58:37.405144 CST
rmgr: Standby     len (rec/tot):     50/    50, tx:          0, lsn: 0/016C1B98, prev 0/016C1B70, desc: RUNNING_XACTS nextXid 565 latestCompletedXid 564 oldestRunningXid 565

可以看出，wal记录的格式是row

checkpoint 的日志输出
随后发现有一些 checkpoint 的日志输出

rmgr: Standby     len (rec/tot):     50/    50, tx:          0, lsn: 0/016C1BD0, prev 0/016C1B98, desc: RUNNING_XACTS nextXid 565 latestCompletedXid 564 oldestRunningXid 565
rmgr: XLOG        len (rec/tot):    106/   106, tx:          0, lsn: 0/016C1C08, prev 0/016C1BD0, desc: CHECKPOINT_ONLINE redo 0/16C1BD0; tli 1; prev tli 1; fpw true; xid 0:565; oid 24576; multi 1; offset 0; oldest xid 548 in DB 1; oldest multi 1 in DB 1; oldest/newest commit timestamp xid: 0/0; oldest running xid 565; online
rmgr: Standby     len (rec/tot):     50/    50, tx:          0, lsn: 0/016C1C78, prev 0/016C1C08, desc: RUNNING_XACTS nextXid 565 latestCompletedXid 564 oldestRunningXid 565
pg_waldump: FATAL:  error in WAL record at 0/16C1C78: invalid record length at 0/16C1CB0: wanted 24, got 0

wal日志记录了数据库集群操作的整个流水，是pitr的关键文件。

pg_waldump pg_xlogdump 的初步使用

pg_waldump –help

分析

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