怎么使用PostgreSQL中pg_waldump工具-创新互联
这篇文章主要介绍“怎么使用PostgreSQL中pg_waldump工具”,在日常操作中,相信很多人在怎么使用PostgreSQL中pg_waldump工具问题上存在疑惑,小编查阅了各式资料,整理出简单好用的操作方法,希望对大家解答”怎么使用PostgreSQL中pg_waldump工具”的疑惑有所帮助!接下来,请跟着小编一起来学习吧!
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注:pg_waldump for PG 10.x+,如果是PG 9.x或以下版本,则使用pg_xlogdump.
一、pg_waldump简介
在Linux下执行,使用--help查看帮助.
[xdb@localhost pg_wal]$ 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, $PGDATA/pg_wal) -r, --rmgr=RMGR only show records generated by resource manager RMGR; use --rmgr=list to list valid resource manager names -s, --start=RECPTR start reading at WAL location RECPTR -t, --timeline=TLI timeline from which to read log records (default: 1 or the value used in STARTSEG) -V, --version output version information, then exit -x, --xid=XID only show records with transaction ID XID -z, --stats[=record] show statistics instead of records (optionally, show per-record statistics) -?, --help show this help, then exit [xdb@localhost pg_wal]$
-b, --bkp-details output detailed information about backup blocks
输出backup blocks即full-write-page的详细信息.
-e, --end=RECPTR stop reading at WAL location RECPTR
搜索在此LSN偏移处结束
-f, --follow keep retrying after reaching end of WAL
在到达WAL末尾时仍继续尝试
-n, --limit=N number of records to display
XLOG Record的输出个数
-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, $PGDATA/pg_wal)
在哪个目录下寻找WAL segment files
-r, --rmgr=RMGR only show records generated by resource manager RMGR;
use --rmgr=list to list valid resource manager names
只显示指定的RMGR的XLOG Record
-s, --start=RECPTR start reading at WAL location RECPTR
在此LSN偏移处开始搜索
-t, --timeline=TLI timeline from which to read log records
(default: 1 or the value used in STARTSEG)
指定的时间线timeline
-V, --version output version information, then exit
输出版本信息,然后退出
-x, --xid=XID only show records with transaction ID XID
只输出指定的事务ID的XLOG Record
-z, --stats[=record] show statistics instead of records
(optionally, show per-record statistics)
输出统计信息
-?, --help show this help, then exit
输出帮助信息
二、pg_waldump使用
下面是测试机上pg_wal目录中的文件
[xdb@localhost pg_wal]$ ll total 98332 -rw-------. 1 xdb xdb 16777216 Dec 20 12:02 000000010000000100000048 -rw-------. 1 xdb xdb 16777216 Dec 19 16:47 000000010000000100000049 -rw-------. 1 xdb xdb 16777216 Dec 19 16:47 00000001000000010000004A -rw-------. 1 xdb xdb 16777216 Dec 19 16:47 00000001000000010000004B -rw-------. 1 xdb xdb 16777216 Dec 19 16:47 00000001000000010000004C -rw-------. 1 xdb xdb 16777216 Dec 19 16:47 00000001000000010000004D drwx------. 2 xdb xdb 6 Nov 16 15:48 archive_status
输出文件000000010000000100000048最开始的4个XLOG Record
命令:pg_waldump -p ./ -s 1/48000000 -n 4
[xdb@localhost pg_wal]$ pg_waldump -p ./ -s 1/48000000 -n 4 rmgr: Heap len (rec/tot): 77/ 77, tx: 1964, lsn: 1/48000070, prev 1/47FFFFF8, desc: INSERT off 117, blkref #0: rel 1663/16402/17028 blk 1110 rmgr: Heap len (rec/tot): 77/ 77, tx: 1964, lsn: 1/480000C0, prev 1/48000070, desc: INSERT off 7, blkref #0: rel 1663/16402/17031 blk 1111 rmgr: Heap len (rec/tot): 77/ 77, tx: 1964, lsn: 1/48000110, prev 1/480000C0, desc: INSERT off 8, blkref #0: rel 1663/16402/17031 blk 1111 rmgr: Heap len (rec/tot): 77/ 77, tx: 1964, lsn: 1/48000160, prev 1/48000110, desc: INSERT off 9, blkref #0: rel 1663/16402/17031 blk 1111
注意第一条记录,上一个LSN为1/47FFFFF8(prev 1/47FFFFF8),提示上一page最后一个XLOG Record存储在本页的XLogLongPageHeaderData中,存储的空间大小可以从该XLOG Record的LSN(1/48000070)和XLogLongPageHeaderData的大小(40B)推算获得,有兴趣的同学可以自行计算.
注:LSN的计算请参照PostgreSQL DBA(15) - WAL文件结构
查看Redo point后的XLOG Record
首先使用pg_controldata命令查看Redo point --> 1/484336A0
[xdb@localhost pg_wal]$ pg_controldata pg_control version number: 1100 Catalog version number: 201809051 Database system identifier: 6624362124887945794 Database cluster state: in production pg_control last modified: Thu 20 Dec 2018 12:17:39 PM CST Latest checkpoint location: 1/484336D8 Latest checkpoint's REDO location: 1/484336A0 Latest checkpoint's REDO WAL file: 000000010000000100000048 Latest checkpoint's TimeLineID: 1 ...
然后使用pg_waldump查看
命令:pg_waldump -p ./ -s 1/484336A0
[xdb@localhost pg_wal]$ pg_waldump -p ./ -s 1/484336A0 rmgr: Standby len (rec/tot): 50/ 50, tx: 0, lsn: 1/484336A0, prev 1/48433668, desc: RUNNING_XACTS nextXid 1971 latestCompletedXid 1970 oldestRunningXid 1971 rmgr: XLOG len (rec/tot): 106/ 106, tx: 0, lsn: 1/484336D8, prev 1/484336A0, desc: CHECKPOINT_ONLINE redo 1/484336A0; tli 1; prev tli 1; fpw true; xid 0:1971; oid 17046; multi 1; offset 0; oldest xid 561 in DB 16402; oldest multi 1 in DB 16402; oldest/newest commit timestamp xid: 0/0; oldest running xid 1971; online rmgr: Standby len (rec/tot): 50/ 50, tx: 0, lsn: 1/48433748, prev 1/484336D8, desc: RUNNING_XACTS nextXid 1971 latestCompletedXid 1970 oldestRunningXid 1971 pg_waldump: FATAL: error in WAL record at 1/48433748: invalid record length at 1/48433780: wanted 24, got 0 [xdb@localhost pg_wal]$
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