在管道末尾将简单记录写入Postgres中的表（可以是任何db）时，某些潜在记录会违反唯一性约束并触发异常。据我所知，没有任何一种可以妥善处理这些问题的直接方法-管道要么完全出错，要么取决于运行程序，从而进入了无限的死亡螺旋。
在光束docs中似乎没有提及这种情况下的错误处理。关于错误处理的媒介posts似乎不适用于返回PDone的这种特殊类型的PTransform。
This的答案难以理解，并且没有示例。
在我的示例中，我正在读取包含2条重复行的文件，并尝试将它们写入表中。
CREATE TABLE foo (
field CHARACTER VARYING(100) UNIQUE
);
foo.txt包含：
a
a
管道如下所示：
Pipeline p = Pipeline.create();
p.apply(TextIO.read().from("/path/to/foo.txt"))
.apply(
JdbcIO.<String>write()
.withDataSourceConfiguration(JdbcIO.DataSourceConfiguration.create("org.postgresql.Driver", "jdbc:postgresql://localhost:5432/somedb"))
.withStatement("INSERT INTO foo (field) VALUES (?)")
.withPreparedStatementSetter(new JdbcIO.PreparedStatementSetter<String>() {
private static final long serialVersionUID = 1L;
public void setParameters(String element, PreparedStatement query) throws SQLException {
query.setString(1, element);
}
}))
;
p.run();
这是上面简单示例的输出：
[WARNING]
org.apache.beam.sdk.Pipeline$PipelineExecutionException: java.sql.BatchUpdateException: Batch entry 0 INSERT INTO foo (field) VALUES ('a') was aborted: ERROR: duplicate key value violates unique constraint "foo_field_key"
Detail: Key (field)=(a) already exists. Call getNextException to see other errors in the batch.
at org.apache.beam.runners.direct.DirectRunner$DirectPipelineResult.waitUntilFinish (DirectRunner.java:332)
at org.apache.beam.runners.direct.DirectRunner$DirectPipelineResult.waitUntilFinish (DirectRunner.java:302)
at org.apache.beam.runners.direct.DirectRunner.run (DirectRunner.java:197)
at org.apache.beam.runners.direct.DirectRunner.run (DirectRunner.java:64)
at org.apache.beam.sdk.Pipeline.run (Pipeline.java:313)
at org.apache.beam.sdk.Pipeline.run (Pipeline.java:299)
at com.thing.Main.main (Main.java:105)
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 org.codehaus.mojo.exec.ExecJavaMojo$1.run (ExecJavaMojo.java:282)
at java.lang.Thread.run (Thread.java:748)
Caused by: java.sql.BatchUpdateException: Batch entry 0 INSERT INTO foo (field) VALUES ('a') was aborted: ERROR: duplicate key value violates unique constraint "foo_field_key"
Detail: Key (field)=(a) already exists. Call getNextException to see other errors in the batch.
at org.postgresql.jdbc.BatchResultHandler.handleError (BatchResultHandler.java:148)
at org.postgresql.core.ResultHandlerDelegate.handleError (ResultHandlerDelegate.java:50)
at org.postgresql.core.v3.QueryExecutorImpl.processResults (QueryExecutorImpl.java:2184)
at org.postgresql.core.v3.QueryExecutorImpl.execute (QueryExecutorImpl.java:481)
at org.postgresql.jdbc.PgStatement.executeBatch (PgStatement.java:840)
at org.postgresql.jdbc.PgPreparedStatement.executeBatch (PgPreparedStatement.java:1538)
at org.apache.commons.dbcp2.DelegatingStatement.executeBatch (DelegatingStatement.java:345)
at org.apache.commons.dbcp2.DelegatingStatement.executeBatch (DelegatingStatement.java:345)
at org.apache.commons.dbcp2.DelegatingStatement.executeBatch (DelegatingStatement.java:345)
at org.apache.commons.dbcp2.DelegatingStatement.executeBatch (DelegatingStatement.java:345)
at org.apache.beam.sdk.io.jdbc.JdbcIO$Write$WriteFn.executeBatch (JdbcIO.java:846)
at org.apache.beam.sdk.io.jdbc.JdbcIO$Write$WriteFn.finishBundle (JdbcIO.java:819)
Caused by: org.postgresql.util.PSQLException: ERROR: duplicate key value violates unique constraint "foo_field_key"
Detail: Key (field)=(a) already exists.
at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse (QueryExecutorImpl.java:2440)
at org.postgresql.core.v3.QueryExecutorImpl.processResults (QueryExecutorImpl.java:2183)
at org.postgresql.core.v3.QueryExecutorImpl.execute (QueryExecutorImpl.java:481)
at org.postgresql.jdbc.PgStatement.executeBatch (PgStatement.java:840)
at org.postgresql.jdbc.PgPreparedStatement.executeBatch (PgPreparedStatement.java:1538)
at org.apache.commons.dbcp2.DelegatingStatement.executeBatch (DelegatingStatement.java:345)
at org.apache.commons.dbcp2.DelegatingStatement.executeBatch (DelegatingStatement.java:345)
at org.apache.commons.dbcp2.DelegatingStatement.executeBatch (DelegatingStatement.java:345)
at org.apache.commons.dbcp2.DelegatingStatement.executeBatch (DelegatingStatement.java:345)
at org.apache.beam.sdk.io.jdbc.JdbcIO$Write$WriteFn.executeBatch (JdbcIO.java:846)
at org.apache.beam.sdk.io.jdbc.JdbcIO$Write$WriteFn.finishBundle (JdbcIO.java:819)
at org.apache.beam.sdk.io.jdbc.JdbcIO$Write$WriteFn$DoFnInvoker.invokeFinishBundle (Unknown Source)
at org.apache.beam.repackaged.beam_runners_direct_java.runners.core.SimpleDoFnRunner.finishBundle (SimpleDoFnRunner.java:285)
at org.apache.beam.repackaged.beam_runners_direct_java.runners.core.SimplePushbackSideInputDoFnRunner.finishBundle (SimplePushbackSideInputDoFnRunner.java:118)
at org.apache.beam.runners.direct.ParDoEvaluator.finishBundle (ParDoEvaluator.java:223)
at org.apache.beam.runners.direct.DoFnLifecycleManagerRemovingTransformEvaluator.finishBundle (DoFnLifecycleManagerRemovingTransformEvaluator.java:73)
at org.apache.beam.runners.direct.DirectTransformExecutor.finishBundle (DirectTransformExecutor.java:188)
at org.apache.beam.runners.direct.DirectTransformExecutor.run (DirectTransformExecutor.java:126)
at java.util.concurrent.Executors$RunnableAdapter.call (Executors.java:511)
at java.util.concurrent.FutureTask.run (FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:624)
at java.lang.Thread.run (Thread.java:748)
我希望能够阻止该异常并将其转移到某些死信构造上。
答案 0 :(得分：0)
在Beam中还没有通用的方法。不时有关于修改IO以不返回PDone的讨论，但据我所知，目前尚无可用的方法。
目前，我可以想到几种解决方法，所有这些都不是理想的选择：