pgsql之查看主备复制延迟_pg如何查看主从复制延迟

查看复制延迟：

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,
       pg_wal_lsn_diff(A .c1, flush_lsn) /(1024 * 1024) AS flush_latency_MB,
       state,
       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 表示从库ip地址。

pg_wal_lsn_diff(lsn pg_lsn, lsn pg_lsn):计算两个预写式日志位置间的差别。

pg_current_wal_lsn()：获得当前预写式日志写入位置

小于10.0版本：

SELECT  
       pg_xlog_location_diff(A .c1, replay_lsn) /(1024 * 1024) AS slave_latency_MB,
       pg_xlog_location_diff(A .c1, sent_lsn) /(1024 * 1024) AS send_latency_MB,
       pg_xlog_location_diff(A .c1, flush_lsn) /(1024 * 1024) AS flush_latency_MB,
       state,
       backend_start,
       now()::timestamp with time zone
   FROM pg_stat_replication, 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 表示从库ip地址。

pg_xlog_location_diff(lsn pg_lsn, lsn pg_lsn):计算两个预写式日志位置间的差别。

pg_current_xlog_location ()：获得当前预写式日志写入位置

大量数据导入和从库备份导致了大量的主从延迟，延迟的wal日志超过wal_keep_segments

造成了主库上的xlog目录被清理，从库需要的日志被清理掉了，最终复制中断。