PostgreSQL演变：“PSQLException：致命：抱歉，已经有太多客户”

Question

我正在尝试建立一个开发PostgreSQL服务器。 它正在运行，我可以从命令行创建角色，表等。 但是当我尝试使用Play应用evolution时，我收到以下错误：

org.postgresql.util.PSQLException: FATAL: sorry, too many clients already

我能够连接，如果我故意输入语法错误，它会返回语法错误，所以我知道Play能够连接到数据库。 但是，在演变成功应用后，我得到上面显示的错误。

我对PostgreSQl管理并不十分精通，所以我不确定问题是Play还是我的PostgreSQL安装。 我刚刚在运行Mountain Lion的Mac上使用Heroku的Postgres.app安装它。

这是写入控制台的内容：

! @6cnb0blpp - Internal server error, for request [GET /] ->

play.api.db.evolutions.InvalidDatabaseRevision: Database 'default' needs evolution! [An SQL script need to be run on your database.]
    at play.api.db.evolutions.EvolutionsPlugin$$anonfun$onStart$1$$anonfun$apply$1.apply$mcV$sp(Evolutions.scala:427) ~[play_2.9.1.jar:2.0.4]
    at play.api.db.evolutions.EvolutionsPlugin.withLock(Evolutions.scala:448) ~[play_2.9.1.jar:2.0.4]
    at play.api.db.evolutions.EvolutionsPlugin$$anonfun$onStart$1.apply(Evolutions.scala:414) ~[play_2.9.1.jar:2.0.4]
    at play.api.db.evolutions.EvolutionsPlugin$$anonfun$onStart$1.apply(Evolutions.scala:412) ~[play_2.9.1.jar:2.0.4]
    at scala.collection.LinearSeqOptimized$class.foreach(LinearSeqOptimized.scala:59) ~[scala-library.jar:0.11.3]
    at scala.collection.immutable.List.foreach(List.scala:45) ~[scala-library.jar:0.11.3]
[error] c.j.b.h.AbstractConnectionHook - Failed to acquire connection Sleeping for 1000ms and trying again. Attempts left: 10. Exception: null
[error] c.j.b.h.AbstractConnectionHook - Failed to acquire connection Sleeping for 1000ms and trying again. Attempts left: 9. Exception: null
[error] c.j.b.h.AbstractConnectionHook - Failed to acquire connection Sleeping for 1000ms and trying again. Attempts left: 8. Exception: null
[error] c.j.b.h.AbstractConnectionHook - Failed to acquire connection Sleeping for 1000ms and trying again. Attempts left: 7. Exception: null
[error] c.j.b.h.AbstractConnectionHook - Failed to acquire connection Sleeping for 1000ms and trying again. Attempts left: 6. Exception: null
[error] c.j.b.h.AbstractConnectionHook - Failed to acquire connection Sleeping for 1000ms and trying again. Attempts left: 5. Exception: null
[error] c.j.b.h.AbstractConnectionHook - Failed to acquire connection Sleeping for 1000ms and trying again. Attempts left: 4. Exception: null
[error] c.j.b.h.AbstractConnectionHook - Failed to acquire connection Sleeping for 1000ms and trying again. Attempts left: 3. Exception: null
[error] c.j.b.h.AbstractConnectionHook - Failed to acquire connection Sleeping for 1000ms and trying again. Attempts left: 2. Exception: null
[error] c.j.b.h.AbstractConnectionHook - Failed to acquire connection Sleeping for 1000ms and trying again. Attempts left: 1. Exception: null
[error] application - 

谢谢！

Answer 1

允许的连接数在postgresql.conf使用GUC（“Grand Unified Configuration”） max_connections 。 默认值为100。

但是，在你修改设置之前，你必须问自己：在你的集群达到极限之前，所有其他100个连接的来源是什么？ 这通常指向您的安装或程序中的错误！

您可能还对连接池和本文关于 Postgres Wiki中的连接数感兴趣。

Answer 2

Postgres.app默认为max_connections = 10.请参阅~/Library/Application Support/Postgres/var/postgresql.conf 。

我通过将max_connections增加到50来修复此问题。在Mountain Lion上，我还必须将shared_buffers减少到500kB才能启动Postgres。

Answer 3

您可以减少应用程序使用的连接数。 在mac安装上有相同的错误。 如官方文档所示：

db.default.partitionCount=2

# The number of connections to create per partition. Setting this to 
# 5 with 3 partitions means you will have 15 unique connections to the 
# database. Note that BoneCP will not create all these connections in   
# one go but rather start off with minConnectionsPerPartition and 
# gradually increase connections as required.
db.default.maxConnectionsPerPartition=5

# The number of initial connections, per partition.
db.default.minConnectionsPerPartition=5