由于缺少驱动程序和数据库之间的连接，Pyspark与PostgreSQL的JDBC连接失败

时间：2017-03-27 12:38:48

标签： postgresql apache-spark jdbc pyspark

我们在EMR集群上使用Pyspark，以便访问和分析PostgreSQL数据库中的数据（可通过jdbc:postgresql://psqlhost:5432/psqldatabase处的JDBC连接器访问）。 EMR集群和PostgreSQL实例之间的网络是开放的，因此，当我们通过SSH访问EMR主机时，我们可以成功启动以下作业（在客户端和集群部署模式下）：

url = 'jdbc:postgresql://psqlhost:5432/psqldatabase'
table = 'mytable'

properties = {
    'user': 'user',
    'password': 'password',
    'driver': 'org.postgresql.Driver'
}

products_df = spark.read.jdbc(url=url, table=table, properties=properties)

我们现在想要从一个单独的客户端实例更改设置并在EMR集群上执行Pyspark命令，并与EMR集群完全连接。通过将必要的纱线配置文件复制到客户端计算机并使用--master yarn执行Pyspark，已成功设置此项。

然而，我们仍然遇到从客户端实例访问PostgreSQL数据库的问题。出于安全原因，客户端计算机无法访问PostgreSQL实例，但该实例仍可由EMR群集访问。上面的代码段对--deploy-mode cluster没有任何问题。但是，在--deploy-mode client中工作时，最后一行会产生以下错误：

17/03/27 11:39:21 ERROR Driver: Connection error: 
org.postgresql.util.PSQLException: The connection attempt failed.
    at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:275)
    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 org.apache.spark.sql.execution.datasources.jdbc.DriverWrapper.connect(DriverWrapper.scala:45)
    at org.apache.spark.sql.execution.datasources.jdbc.JdbcUtils$$anonfun$createConnectionFactory$2.apply(JdbcUtils.scala:65)
    at org.apache.spark.sql.execution.datasources.jdbc.JdbcUtils$$anonfun$createConnectionFactory$2.apply(JdbcUtils.scala:56)
    at org.apache.spark.sql.execution.datasources.jdbc.JDBCRDD$.resolveTable(JDBCRDD.scala:123)
    at org.apache.spark.sql.execution.datasources.jdbc.JDBCRelation.<init>(JDBCRelation.scala:117)
    at org.apache.spark.sql.DataFrameReader.jdbc(DataFrameReader.scala:237)
    at org.apache.spark.sql.DataFrameReader.jdbc(DataFrameReader.scala:159)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:237)
    at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:357)
    at py4j.Gateway.invoke(Gateway.java:280)
    at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:128)
    at py4j.commands.CallCommand.execute(CallCommand.java:79)
    at py4j.GatewayConnection.run(GatewayConnection.java:211)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.net.SocketTimeoutException: connect timed out
    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)
    ... 22 more
---------------------------------------------------------------------------
Py4JJavaError                             Traceback (most recent call last)
<ipython-input-2-f5f370f4d567> in <module>()
----> 1 products_df = spark.read.jdbc(url=url, table=table, properties=properties)

/opt/spark-2.0.0/python/pyspark/sql/readwriter.pyc in jdbc(self, url, table, column, lowerBound, upperBound, numPartitions, predicates, properties)
    420             jpredicates = utils.toJArray(gateway, gateway.jvm.java.lang.String, predicates)
    421             return self._df(self._jreader.jdbc(url, table, jpredicates, jprop))
--> 422         return self._df(self._jreader.jdbc(url, table, jprop))
    423 
    424 

/opt/spark-2.0.0/python/lib/py4j-0.10.1-src.zip/py4j/java_gateway.py in __call__(self, *args)
    931         answer = self.gateway_client.send_command(command)
    932         return_value = get_return_value(
--> 933             answer, self.gateway_client, self.target_id, self.name)
    934 
    935         for temp_arg in temp_args:

/opt/spark-2.0.0/python/pyspark/sql/utils.pyc in deco(*a, **kw)
     61     def deco(*a, **kw):
     62         try:
---> 63             return f(*a, **kw)
     64         except py4j.protocol.Py4JJavaError as e:
     65             s = e.java_exception.toString()

/opt/spark-2.0.0/python/lib/py4j-0.10.1-src.zip/py4j/protocol.py in get_return_value(answer, gateway_client, target_id, name)
    310                 raise Py4JJavaError(
    311                     "An error occurred while calling {0}{1}{2}.\n".
--> 312                     format(target_id, ".", name), value)
    313             else:
    314                 raise Py4JError(

Py4JJavaError: An error occurred while calling o47.jdbc.
: org.postgresql.util.PSQLException: The connection attempt failed.
    at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:275)
    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 org.apache.spark.sql.execution.datasources.jdbc.DriverWrapper.connect(DriverWrapper.scala:45)
    at org.apache.spark.sql.execution.datasources.jdbc.JdbcUtils$$anonfun$createConnectionFactory$2.apply(JdbcUtils.scala:65)
    at org.apache.spark.sql.execution.datasources.jdbc.JdbcUtils$$anonfun$createConnectionFactory$2.apply(JdbcUtils.scala:56)
    at org.apache.spark.sql.execution.datasources.jdbc.JDBCRDD$.resolveTable(JDBCRDD.scala:123)
    at org.apache.spark.sql.execution.datasources.jdbc.JDBCRelation.<init>(JDBCRelation.scala:117)
    at org.apache.spark.sql.DataFrameReader.jdbc(DataFrameReader.scala:237)
    at org.apache.spark.sql.DataFrameReader.jdbc(DataFrameReader.scala:159)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:237)
    at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:357)
    at py4j.Gateway.invoke(Gateway.java:280)
    at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:128)
    at py4j.commands.CallCommand.execute(CallCommand.java:79)
    at py4j.GatewayConnection.run(GatewayConnection.java:211)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.net.SocketTimeoutException: connect timed out
    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)
    ... 22 more

失败的原因可能是应用程序驱动程序（在--deploy-mode client中存在于客户端计算机上）尝试连接到PostgreSQL实例，但是由于无法从客户端访问PostgreSQL实例而失败。但是，我不明白为什么应该要求连接driver-postgreSQL：当在数据帧上执行实际操作时，实际操作将由集群上的机器执行（而不是由客户机上的驱动程序执行），并且结果将通过集群主机发送回驱动程序。因此，只要可以从集群中访问postgreSQL实例，缺少连接driver-postgreSQL就不应该阻止执行数据帧操作。

问题：

  • 驱动程序必须能够连接到数据库才能执行操作吗？
  • 有什么理由说明为什么我必须建立这种连接？
  • 如果不是这样，我们是否可以绕过此连接检查？

1 个答案:

答案 0 :(得分：0)

正如Samson Scharfrichter所指出的，驱动程序需要能够访问数据库才能获取架构。

不幸的是，我们的客户端无法直接访问数据库。但是，由于EMR集群可以访问数据库并且客户端具有对集群的SSH访问权限，因此我们可以使用基于SSH隧道的以下解决方法：

products_df

在此步骤之后，即使隧道关闭，也可以操纵数据帧FATAL EXCEPTION: IntentService[] Process: com.frenzin.alert, PID: 5892 java.lang.SecurityException: getDeviceId: Neither user 10240 nor current process has android.permission.READ_PHONE_STATE. at android.os.Parcel.readException(Parcel.java:1620) at android.os.Parcel.readException(Parcel.java:1573) at com.android.internal.telephony.ITelephony$Stub$Proxy.getDeviceId(ITelephony.java:4207) at android.telephony.TelephonyManager.getDeviceId(TelephonyManager.java:706) at com.frenzin.alert.RegistrationIntentService.onHandleIntent(RegistrationIntentService.java:44) at android.app.IntentService$ServiceHandler.handleMessage(IntentService.java:66) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:148) at android.os.HandlerThread.run(HandlerThread.java:61) 。通过此解决方法，客户端计算机甚至可以在客户端部署模式下查询数据库。

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