作者
digoal
日期
2021-01-07
标签
PostgreSQL , GUC , 参数 , in_hot_standby
背景
PostgreSQL 新增参数in_hot_standby , 用于判断当前实例是否处于recovery状态(内部调用RecoveryInProgress得到), 可以用来判断是否处于standby角色.
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=bf8a662c9afad6fd07b42cdc5e71416c51f75d31
```
Introduce a new GUC_REPORT setting "in_hot_standby".
author Tom Lane tgl@sss.pgh.pa.us
Tue, 5 Jan 2021 21:18:01 +0000 (16:18 -0500)
committer Tom Lane tgl@sss.pgh.pa.us
Tue, 5 Jan 2021 21:18:05 +0000 (16:18 -0500)
commit bf8a662c9afad6fd07b42cdc5e71416c51f75d31
tree 6b2d6c2e185a0dd4897101935d69ef3d5b3969cd tree | snapshot
parent 47b2ed1d06c1218eee8869c8eca8bf002b9d43a6 commit | diff
Introduce a new GUC_REPORT setting "in_hot_standby".
Aside from being queriable via SHOW, this value is sent to the client
immediately at session startup, and again later on if the server gets
promoted to primary during the session. The immediate report will be
used in an upcoming patch to avoid an extra round trip when trying to
connect to a primary server.
Haribabu Kommi, Greg Nancarrow, Tom Lane; reviewed at various times
by Laurenz Albe, Takayuki Tsunakawa, Peter Smith.
Discussion: https://postgr.es/m/CAF3+xM+8-ztOkaV9gHiJ3wfgENTq97QcjXQt+rbFQ6F7oNzt9A@mail.gmail.com
```
+static const char *
+show_in_hot_standby(void)
+{
+ /*
+ * We display the actual state based on shared memory, so that this GUC
+ * reports up-to-date state if examined intra-query. The underlying
+ * variable in_hot_standby changes only when we transmit a new value to
+ * the client.
+ */
+ return RecoveryInProgress() ? "on" : "off";
+}
show in_hot_standby; 判断当前数据库是否处于recovery状态.
使用pg_is_in_recovery函数也能得到相同结果.
```
postgres=> select pg_is_in_recovery();
pg_is_in_recovery
f
(1 row)
```
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