PostgreSQL演變：“PSQLException：致命：抱歉，已經有太多客戶”

Question

我正在嘗試建立一個開發PostgreSQL服務器。 它正在運行，我可以從命令行創建角色，表等。 但是當我嘗試使用Play應用evolution時，我收到以下錯誤：

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

我能夠連接，如果我故意輸入語法錯誤，它會返回語法錯誤，所以我知道Play能夠連接到數據庫。 但是，在演變成功應用后，我得到上面顯示的錯誤。

我對PostgreSQl管理並不十分精通，所以我不確定問題是Play還是我的PostgreSQL安裝。 我剛剛在運行Mountain Lion的Mac上使用Heroku的Postgres.app安裝它。

這是寫入控制台的內容：

! @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 - 

謝謝！

Answer 1

允許的連接數在postgresql.conf使用GUC（“Grand Unified Configuration”） max_connections 。 默認值為100。

但是，在你修改設置之前，你必須問自己：在你的集群達到極限之前，所有其他100個連接的來源是什么？ 這通常指向您的安裝或程序中的錯誤！

您可能還對連接池和本文關於 Postgres Wiki中的連接數感興趣。

Answer 2

Postgres.app默認為max_connections = 10.請參閱~/Library/Application Support/Postgres/var/postgresql.conf 。

我通過將max_connections增加到50來修復此問題。在Mountain Lion上，我還必須將shared_buffers減少到500kB才能啟動Postgres。

Answer 3

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。 如官方文檔所示：

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