PostgreSQL演變：「PSQLException：致命：對不起，客戶已經太多了」

Question

我正在嘗試設置開發PostgreSQL服務器。它正在運行，我可以從命令行創建角色，表等。然而，當我嘗試使用播放應用變陣，我得到以下錯誤：

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

我能夠連接，如果我把故意語法錯誤，它讓我知道，玩返回語法錯誤能夠連接到數據庫。但是，在演變成功應用後，我得到上面顯示的錯誤。

我對PostgreSQl管理並不十分精通，所以我不確定問題出在Play或PostgreSQL安裝上。我只是在運行Mountain Lion的Mac上使用Heroku的Postgres.app安裝它。

這裏是被寫入到控制檯：

! @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 - 

謝謝！

Answer 1

您可以減少應用程序使用的連接數。在mac安裝上有相同的錯誤。如圖中official documentation：

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 

Answer 2

使用GUC（「Grand Unified Configuration」）max_connections在postgresql.conf中設置允許的連接數。默認值爲100.

但是在您修補設置之前，您必須問自己：在您的羣集達到限制之前，所有其他100個連接都來自哪裏？這通常指向您的安裝或程序中的錯誤！

您可能也有興趣connection pooling和article about The Number of Connections在Postgres Wiki中。

Answer 3

Postgres.app默認爲MAX_CONNECTIONS = 10。參見~/Library/Application Support/Postgres/var/postgresql.conf。

我通過將max_connections增加到50來解決這個問題。在Mountain Lion，我還必須將shared_buffers減少到500kB以便Postgres啓動。