PostgreSQL的pg_xlog下有大量日志，空间不足，如何删除？

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Darren1:postgres:/usr/local/pgsql/data/pg_xlog:>ls

000000010000000000000008.00000028.backup  00000001000000000000009D  0000000100000000000000C9  0000000100000000000000F5  000000010000000100000021  00000001000000010000004D

000000010000000000000072                  00000001000000000000009E  0000000100000000000000CA  0000000100000000000000F6  000000010000000100000022  00000001000000010000004E

000000010000000000000073                  00000001000000000000009F  0000000100000000000000CB  0000000100000000000000F7  000000010000000100000023  00000001000000010000004F

......

Darren1:postgres:/usr/local/pgsql/data/pg_xlog:>ll|wc -l

263

Darren1:postgres:/usr/local/pgsql/data/pg_xlog:>du -sh /usr/local/pgsql/data/pg_xlog/

4.1G    /usr/local/pgsql/data/pg_xlog/

清理步骤：

pg_resetxlog用来清理WAL日志，当数据库服务启动的情况下，是不能使用的，所以执行之前需要停机。

(1)停机

Darren1:postgres:/usr/local/pgsql/bin:>pg_ctl stop -m fast

(2)查看NextXID和NextOID(发生checkpoint的时候，这两个值会发生改变)

Darren1:postgres:/usr/local/pgsql/bin:>pg_controldata

pg_control version number:            960

Catalog version number:               201608131

Database system identifier:           6446917631406040181

Database cluster state:               shut down

pg_control last modified:             Thu 27 Jul 2017 05:04:12 AM CST

Latest checkpoint location:           1/73000028

Prior checkpoint location:            1/720048F8

Latest checkpoint's REDO location:    1/73000028

Latest checkpoint's REDO WAL file:    000000010000000100000073

Latest checkpoint's TimeLineID:       1

Latest checkpoint's PrevTimeLineID:   1

Latest checkpoint's full_page_writes: on

Latest checkpoint's NextXID:          0:19545

Latest checkpoint's NextOID:          16646

......

(3)使用pg_resetxlog，指定oid和xid

Darren1:postgres:/usr/local/pgsql/bin:>pg_resetxlog -o 16646 -x 19545 -f /usr/local/pgsql/data/

Transaction log reset

Darren1:postgres:/usr/local/pgsql/data/pg_xlog:>ll

-rw-------. 1 postgres dba      302 Jul 26 12:12 000000010000000000000008.00000028.backup

-rw-------. 1 postgres dba 16777216 Jul 27 05:07 000000010000000100000077

drwx------. 2 postgres dba    20480 Jul 27 05:07 archive_status

Darren1:postgres:/usr/local/pgsql/data/pg_xlog:>du -sh /usr/local/pgsql/data/pg_xlog/

17M    /usr/local/pgsql/data/pg_xlog/

(4)启动数据库

Darren1:postgres:/usr/local/pgsql/data/pg_xlog:>pg_ctl start

当前名称：pg_resetxlog清理的pg_xlog下的WAL日志
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