PostgreSQL的pg_xlog下有大量日志，空間不足，如何刪除？

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/

清理步驟：

pg_resetxlog用來清理WAL日志，當數據庫服務啟動的情況下，是不能使用的，所以執行之前需要停機。

(1)停機

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

(2)查看NextXID和NextOID(發生checkpoint的時候，這兩個值會發生改變)

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)啟動數據庫

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