如何檢視主從複製的狀態，且備庫應用落後了多少位元組

這些資訊要在主庫中查詢

檢視流複製的資訊可以使用主庫上的檢視

select pid,state,client_addr,sync_priority,sync_state from pg_stat_replication;

pg_stat_replication中幾個字斷記錄了傳送wal的位置及備庫接收到的wal的位置、

sent_location--傳送wal的位置

write_location--備庫接收到的wal的位置

flush_location—備庫寫wal日誌到磁碟的位置

replay_location—備庫應用日誌的位置

檢視備庫落後主庫多少位元組

select pg_xlog_location_diff(pg_current_xlog_location(),replay_location)/1024/1024 as MB from pg_stat_replication;
select pg_xlog_location_diff(pg_current_xlog_location(),replay_location)/1024/1024/1024 as GB from pg_stat_replication;

級聯複製

select pg_xlog_location_diff(pg_last_xlog_replay_location(),replay_location)/1024/1024/1024 as GB from pg_stat_replication;

補充：pgsql之檢視主備複製延遲

檢視複製延遲：

10.0及以上：

SELECT 
  pg_wal_lsn_diff(A .c1,replay_lsn) /(1024 * 1024) AS slave_latency_MB,pg_wal_lsn_diff(A .c1,sent_lsn) /(1024 * 1024) AS send_latency_MB,flush_lsn) /(1024 * 1024) AS flush_latency_MB,backend_start,now()::timestamp with time zone
 FROM pg_stat_replication,pg_current_wal_lsn() AS A(c1)
 WHERE client_addr='192.168.46.173' and application_name = 'standby1'
 ORDER BY slave_latency_MB,send_latency_MB DESC
 LIMIT 1;

注：

192.168.46.173 表示從庫ip地址。

pg_wal_lsn_diff(lsn pg_lsn,lsn pg_lsn):計算兩個預寫式日誌位置間的差別。

pg_current_wal_lsn()：獲得當前預寫式日誌寫入位置

小於10.0版本：

SELECT 
  pg_xlog_location_diff(A .c1,pg_xlog_location_diff(A .c1,pg_current_xlog_location AS A(c1)
 WHERE client_addr='192.168.46.173' and application_name = 'standby1'
 ORDER BY slave_latency_MB,send_latency_MB DESC
 LIMIT 1;

注：

192.168.46.173 表示從庫ip地址。

pg_xlog_location_diff(lsn pg_lsn,lsn pg_lsn):計算兩個預寫式日誌位置間的差別。

pg_current_xlog_location ()：獲得當前預寫式日誌寫入位置

以上為個人經驗，希望能給大家一個參考，也希望大家多多支援我們。如有錯誤或未考慮完全的地方，望不吝賜教。