检查异步流复制情况：
主库查询：
select pid,state,client_addr,sync_priority,sync_state from pg_stat_replication;
 
postgres=# \d pg_stat_replication;
          View "pg_catalog.pg_stat_replication"
      Column      |           Type           | Modifiers
------------------+--------------------------+-----------
 pid              | integer                  |
 usesysid         | oid                      |
 usename          | name                     |
 application_name | text                     |
 client_addr      | inet                     |
 client_hostname  | text                     |
 client_port      | integer                  |
 backend_start    | timestamp with time zone |
 backend_xmin     | xid                      |
 state            | text                     |
 sent_location    | pg_lsn                   |
 write_location   | pg_lsn                   |
 flush_location   | pg_lsn                   |
 replay_location  | pg_lsn                   |
 sync_priority    | integer                  |
 sync_state       | text                     |
 
 
 
查看备库落后主库多少字节的WAL日志：
select pg_xlog_location_diff(pg_current_xlog_location(),replay_location) from pg_stat_replication;
 
检查同步流复制的情况：
select pid,sync_state from pg_stat_replication;
 
将主库上WAL位置转换为WAL文件名和偏移量：
select * from pg_xlogfile_name_offset('');
postgres=# select write_location from pg_stat_replication;
 write_location
----------------
 0/15008550
(1 row)
 
postgres=# select * from pg_xlogfile_name_offset('0/15008550');
        file_name         | file_offset
--------------------------+-------------
 000000010000000000000015 |       34128
(1 row)
 
postgres=#
 
 
查看备库状态：
select pg_is_in_recovery();  --主库为f，备库为t
如果不能连进去，可以用命令行工具：
pg_controldata
 
在hot standby，查看备库接收WAL日志和应用WAL日志的状态：
pg_last_xlog_receive_location()
pg_last_xlog_replay_location()
pg_last_xact_replay_timestamp()