Question

我设置了一个分布式postgres数据库系统，并使用hot_standby wal_level配置了复制。

有一个中央主数据库，其中有多个副本（目前全世界有15个）用作只读实例 - 因此不需要故障转移 - 我们只想将数据同步到我们可以读取的远程位置它们。

主：

wal_level = hot_standby
max_wal_senders = 20
checkpoint_segments = 8    
wal_keep_segments = 8

客户端：

wal_level = hot_standby
max_wal_senders = 3
checkpoint_segments = 8    
wal_keep_segments = 8 
hot_standby = on

客户端的

/var/lib/postgresql/9.4/recovery.conf：

standby_mode = 'on'
primary_conninfo = 'host=<IP of master> port=5432 user=replicator password=xxxx sslmode=require'
trigger_file = '/tmp/postgresql.trigger'

复制开始 - 有些日子似乎都很好。几天之后，主人似乎没有接受更多连接进行复制......

客户：

2017-05-04 01:16:51 UTC [9608-1] FATAL:  could not connect to the primary server: FATAL:  sorry, too many clients already
2017-05-04 01:16:57 UTC [10807-1] FATAL:  could not connect to the primary server: FATAL:  sorry, too many clients already
2017-05-04 01:17:02 UTC [12022-1] FATAL:  could not connect to the primary server: FATAL:  sorry, too many clients already
2017-05-04 01:17:06 UTC [13217-1] FATAL:  could not connect to the primary server: FATAL:  remaining connection slots are reserved for non-replication superuser connections
...

主：

然后loag充满了下面的消息 - 它永远不会恢复......

2017-05-04 08:44:14 UTC [24850-1] replicator@[unknown] ERROR:  requested WAL segment 000000010000003500000014 has already been removed
2017-05-04 08:44:19 UTC [25958-1] replicator@[unknown] ERROR:  requested WAL segment 000000010000003500000014 has already been removed
2017-05-04 08:44:24 UTC [27063-1] replicator@[unknown] ERROR:  requested WAL segment 000000010000003500000014 has already been removed
2017-05-04 08:44:29 UTC [28144-1] replicator@[unknown] ERROR:  requested WAL segment 000000010000003500000014 has already been removed
2017-05-04 08:44:34 UTC [29227-1] replicator@[unknown] ERROR:  requested WAL segment 000000010000003500000014 has already been removed
2017-05-04 08:44:39 UTC [30316-1] replicator@[unknown] ERROR:  requested WAL segment 000000010000003500000014 has already been removed
...

客户端：

2017-04-30 11:26:22 UTC [28474-1] LOG:  started streaming WAL from primary at 35/14000000 on timeline 1
2017-04-30 11:26:22 UTC [28474-2] FATAL:  could not receive data from WAL stream: ERROR:  requested WAL segment 000000010000003500000014 has already been removed
2017-04-30 11:26:26 UTC [29328-1] LOG:  started streaming WAL from primary at 35/14000000 on timeline 1
2017-04-30 11:26:26 UTC [29328-2] FATAL:  could not receive data from WAL stream: ERROR:  requested WAL segment 000000010000003500000014 has already been removed
2017-04-30 11:26:31 UTC [30394-1] LOG:  started streaming WAL from primary at 35/14000000 on timeline 1
2017-04-30 11:26:31 UTC [30394-2] FATAL:  could not receive data from WAL stream: ERROR:  requested WAL segment 000000010000003500000014 has already been removed
...

所以我的问题：

是否有更好的方法只是将更改同步到远程只读实例，或者我只是在配置中出现错误，使我的复制在一段时间后中断？

Answer 1

https://www.postgresql.org/docs/current/static/runtime-config-replication.html：

max_wal_senders（整数）

指定备用数据库的最大并发连接数   服务器或流基备份客户端（即最大数量   同时运行WAL发送器进程）。默认值为零，   意味着禁用复制。 WAL发送者进程计入   连接总数，因此参数不能设置得更高   比max_connections。 突发的流媒体客户端可能会断开连接   导致孤立的连接槽，直到达到超时，所以这个   参数应设置略高于最大数量   预期客户所以断开连接的客户可以立即重新连接。

（强调我的）。应用程序连接或孤立连接导致您的

FATAL: sorry, too many clients already

您可能希望为应用程序使用某些连接池，例如pgbouncer，在实际发生之前限制太多连接。

如果您have archive_command设置为在某处实际复制WAL，请回答您的问题，修改slave上recovery.conf中的restore_command以获取它们。它将允许奴隶从失去的那一刻开始追赶。否则你必须重建它。

分发的postgres部署不同步

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