在没有数据库的情况下启动Java / Play2.5 REST API

Question

我想开始我的Java / Play！ 即使无法访问数据库也可以提供服务。 到目前为止，如果数据库不可用，该服务将停止。 在Play中，是否有可能尝试每秒重新连接一次而没有完全停止服务并在连接可用后立即重新连接到db。

我们的application.conf当前看起来像这样：

play.evolutions.enabled=false
//play.db.pool=bonecp

db {
   default.driver=org.postgresql.Driver
   default.url="jdbc:postgresql://postgresdb.postgres:5432/postcode"
   default.username="<username>"
   default.password="<strong-password>"
}

play.db {
  config = "db"
  prototype.hikaricp = {
    connectionTimeout = 250 milliseconds
    initializationFailFast = false
    readOnly = true
  }
}

ebean.default = ["models.*"]

目前，我得到以下日志：

2017-05-15 13:26:54.525 [error] postcode-play: Connection error: 
org.postgresql.util.PSQLException: FATAL: remaining connection slots are reserved for non-replication superuser connections
  Ort: Datei: postinit.c, Routine: InitPostgres, Zeile: 779.
  Server SQLState: 53300
    at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2412)
    at org.postgresql.core.v3.QueryExecutorImpl.readStartupMessages(QueryExecutorImpl.java:2538)
    at org.postgresql.core.v3.QueryExecutorImpl.<init>(QueryExecutorImpl.java:122)
    at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:227)
    at org.postgresql.core.ConnectionFactory.openConnection(ConnectionFactory.java:49)
    at org.postgresql.jdbc.PgConnection.<init>(PgConnection.java:194)
    at org.postgresql.Driver.makeConnection(Driver.java:431)
    at org.postgresql.Driver.connect(Driver.java:247)
    at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:95)
    at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:101)

2017-05-15 13:26:54.626 [error] postcode-play: Connection error: 
org.postgresql.util.PSQLException: FATAL: remaining connection slots are reserved for non-replication superuser connections
  Ort: Datei: postinit.c, Routine: InitPostgres, Zeile: 779.
  Server SQLState: 53300
    at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2412)
    at org.postgresql.core.v3.QueryExecutorImpl.readStartupMessages(QueryExecutorImpl.java:2538)
    at org.postgresql.core.v3.QueryExecutorImpl.<init>(QueryExecutorImpl.java:122)
    at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:227)
    at org.postgresql.core.ConnectionFactory.openConnection(ConnectionFactory.java:49)
    at org.postgresql.jdbc.PgConnection.<init>(PgConnection.java:194)
    at org.postgresql.Driver.makeConnection(Driver.java:431)
    at org.postgresql.Driver.connect(Driver.java:247)
    at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:95)
    at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:101)
.
.
.

指示服务器没有完全停止，而是尝试按需要多次连接到db。 但是，如果数据库可用，则会写入以下日志：

2017-05-15 14:08:43.748 [error] postcode-play: 

! @7430ed7gf - Internal server error, for (GET) [/?postcode=88682&country=DE] ->

play.api.Configuration$$anon$1: Configuration error[Cannot connect to database [default]]
    at play.api.Configuration$.configError(Configuration.scala:155)
    at play.api.Configuration.reportError(Configuration.scala:808)
    at play.api.db.DefaultDBApi$$anonfun$connect$1.apply(DefaultDBApi.scala:48)
    at play.api.db.DefaultDBApi$$anonfun$connect$1.apply(DefaultDBApi.scala:42)
    at scala.collection.immutable.List.foreach(List.scala:392)
    at play.api.db.DefaultDBApi.connect(DefaultDBApi.scala:42)
    at play.api.db.DBApiProvider.get$lzycompute(DBModule.scala:72)
    at play.api.db.DBApiProvider.get(DBModule.scala:62)
    at play.api.db.DBApiProvider.get(DBModule.scala:58)
    at com.google.inject.internal.ProviderInternalFactory.provision(ProviderInternalFactory.java:81)
Caused by: java.sql.SQLTransientConnectionException: HikariPool-4 - Connection is not available, request timed out after 5001ms.
    at com.zaxxer.hikari.pool.HikariPool.createTimeoutException(HikariPool.java:548)
    at com.zaxxer.hikari.pool.HikariPool.getConnection(HikariPool.java:186)
    at com.zaxxer.hikari.pool.HikariPool.getConnection(HikariPool.java:145)
    at com.zaxxer.hikari.HikariDataSource.getConnection(HikariDataSource.java:83)
    at play.api.db.DefaultDatabase.getConnection(Databases.scala:142)
    at play.api.db.DefaultDatabase.getConnection(Databases.scala:138)
    at play.api.db.DefaultDBApi$$anonfun$connect$1.apply(DefaultDBApi.scala:44)
    at play.api.db.DefaultDBApi$$anonfun$connect$1.apply(DefaultDBApi.scala:42)
    at scala.collection.immutable.List.foreach(List.scala:392)
    at play.api.db.DefaultDBApi.connect(DefaultDBApi.scala:42)
Caused by: org.postgresql.util.PSQLException: Connection to localhost:5432 refused. Check that the hostname and port are correct and that the postmaster is accepting TCP/IP connections.
    at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:265)
    at org.postgresql.core.ConnectionFactory.openConnection(ConnectionFactory.java:49)
    at org.postgresql.jdbc.PgConnection.<init>(PgConnection.java:194)
    at org.postgresql.Driver.makeConnection(Driver.java:431)
    at org.postgresql.Driver.connect(Driver.java:247)
    at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:95)
    at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:101)
    at com.zaxxer.hikari.pool.PoolBase.newConnection(PoolBase.java:341)
    at com.zaxxer.hikari.pool.PoolBase.newPoolEntry(PoolBase.java:193)
    at com.zaxxer.hikari.pool.HikariPool.createPoolEntry(HikariPool.java:430)
Caused by: java.net.ConnectException: Verbindungsaufbau abgelehnt (Connection refused)
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.net.Socket.connect(Socket.java:589)
    at org.postgresql.core.PGStream.<init>(PGStream.java:62)
    at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:144)
    at org.postgresql.core.ConnectionFactory.openConnection(ConnectionFactory.java:49)
    at org.postgresql.jdbc.PgConnection.<init>(PgConnection.java:194
)

即使服务器现在可用，也无法与数据库联系。 如果我重新启动服务器，将找到数据库并且可以使用该数据库，但是数据库始终必须在启动时存在。 如何解决此问题，以便可以独立于数据库启动应用程序？

如果数据库在应用程序启动后变得不可用，则在数据库再次变得可用之后没有问题。 它会自动重新连接。

非常感谢您的帮助！

Answer 1

似乎您在向Postgres开放一些联系。 这些连接必须关闭 ，否则Postgres将达到其max_connections限制。

您可以增加max_connections但不建议这样做，因为如果设置得太高，Postgres的性能将会降低。 此外，当您使用HikariCP时，看看HikariCP文档并不是一个坏主意，特别是idleTimeout和minimumIdle配置变量应该可以为您提供帮助。

如果上述方法不起作用，则必须确切确认与Postgres建立了多少连接。 甚至可以检查您个人通过SSH或其他应用与Postgres进行的会话数，而不仅仅是Play框架连接数。