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https://issues.apache.org/jira/browse/CALCITE-5099?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17540245#comment-17540245
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Julian Hyde commented on CALCITE-5099:
--------------------------------------
It looks as it {{LimitIterator}} is the culprit. We need something that
implements {{AutoCloseable}} or at least {{Closeable}}.
{{Enumerable.takeWhile(Predicate2)}} should be able to do the job.
And then we need {{MetaImpl.collect}} to check whether the {{Iterable}}
implements {{Closeable}} and if so call {{close}} when done. Probably create a
new {{collect}} method that takes {{Enumerable}} and have the old
implementation delegate to it.
> ResultSetEnumerable.enumeratorBasedOnStatement cause the backend connection
> leak
> ---------------------------------------------------------------------------------
>
> Key: CALCITE-5099
> URL: https://issues.apache.org/jira/browse/CALCITE-5099
> Project: Calcite
> Issue Type: Bug
> Components: avatica, core
> Affects Versions: 1.30.0
> Reporter: itxiangkui
> Priority: Major
> Labels: connection, connection-pooling, leak
>
> We have extended JdbcSchema and JdbcCatalogSchema in order to connect to the
> back-end mysql database.
> At the same time, HikariDataSource was used to replace the original
> BasicDataSource. When the connection pool leak detection of HikariDataSource
> was activated, a connection leak was detected.
> {code:java}
> java.lang.Exception: Apparent connection leak detected
> at
> com.zaxxer.hikari.HikariDataSource.getConnection(HikariDataSource.java:128)
> at
> org.apache.calcite.runtime.ResultSetEnumerable.enumeratorBasedOnStatement(ResultSetEnumerable.java:267)
> at
> org.apache.calcite.runtime.ResultSetEnumerable.enumerator(ResultSetEnumerable.java:257)
> at
> org.apache.calcite.linq4j.AbstractEnumerable.iterator(AbstractEnumerable.java:33)
> at
> org.apache.calcite.jdbc.CalciteMetaImpl.fetch(CalciteMetaImpl.java:674)
> at
> org.apache.calcite.avatica.remote.LocalService.apply(LocalService.java:245)
> at
> org.apache.calcite.avatica.remote.Service$FetchRequest.accept(Service.java:1395)
> at
> org.apache.calcite.avatica.remote.Service$FetchRequest.accept(Service.java:1362)
> at
> org.apache.calcite.avatica.remote.AbstractHandler.apply(AbstractHandler.java:94)
> at
> org.apache.calcite.avatica.remote.JsonHandler.apply(JsonHandler.java:52)
> at
> org.apache.calcite.avatica.server.AvaticaJsonHandler.handle(AvaticaJsonHandler.java:133)
> at
> org.eclipse.jetty.server.handler.HandlerList.handle(HandlerList.java:59)
> at
> org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:127)
> at org.eclipse.jetty.server.Server.handle(Server.java:500)
> at
> org.eclipse.jetty.server.HttpChannel.lambda$handle$1(HttpChannel.java:383)
> at org.eclipse.jetty.server.HttpChannel.dispatch(HttpChannel.java:547)
> at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:375)
> at
> org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:270)
> at
> org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:311)
> at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:103)
> at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:117)
> at
> org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.runTask(EatWhatYouKill.java:336)
> at
> org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:313)
> at
> org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.tryProduce(EatWhatYouKill.java:171)
> at
> org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:129)
> at
> org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:388)
> at
> org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:806)
> at
> org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:938)
> at java.lang.Thread.run(Thread.java:748)
> {code}
> Navigating to the snippet is
> {code:java}
> private Enumerator<T> enumeratorBasedOnStatement() {
> Connection connection = null;
> Statement statement = null;
> try {
> connection = dataSource.getConnection();
> statement = connection.createStatement();
> setTimeoutIfPossible(statement);
> if (statement.execute(sql)) {
> final ResultSet resultSet = statement.getResultSet();
> statement = null;
> connection = null;
> return new ResultSetEnumerator<>(resultSet, rowBuilderFactory);
> } else {
> Integer updateCount = statement.getUpdateCount();
> //noinspection unchecked
> return Linq4j.singletonEnumerator((T) updateCount);
> }
> } catch (SQLException e) {
> throw Static.RESOURCE.exceptionWhilePerformingQueryOnJdbcSubSchema(sql)
> .ex(e);
> } finally {
> closeIfPossible(connection, statement);
> }
> }
> {code}
> obviously when you set:
> *statement = null;*
> *connection = null;*
> {code:java}
> if (statement.execute(sql)) {
> final ResultSet resultSet = statement.getResultSet();
> statement = null;
> connection = null;
> return new ResultSetEnumerator<>(resultSet, rowBuilderFactory);
> }
> {code}
> the connection may leak,closeIfPossible(connection, statement); will close a
> null connection
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