Marcio Sugar edited comment on NIFI-4926 at 3/3/18 12:13 AM:

In {{QueryDatabaseTable.java}}, method {{onTrigger}}, line 278, a JDBC result 
set is created but not used to control the _while_ loop two lines below. In 
fact, the {{resultSet}} is handled to another method, 
{{JdbcCommon.convertToAvroStream}}, which does its job and returns the number 
of rows it used to populate the output Avro file.

Because only the number of rows is returned, {{QueryDatabaseTable}} doesn't 
know the last {{rs.next()}} was false, which means (at least for the DB2 JDBC 
Driver) the result set is now closed. Instead of breaking out of the while 
loop, the processor once again calls {{convertToAvroStream}} and a 
{{SqlException}} is thrown soon after.

 * Perhaps this logic works fine for other databases, but considering 
{{resultSet}} was not created with try-with-resouces and I couldn't find any 
explicit {{resultSet.close()}}, it stands to reason we could also have a 
resource leakage here.
 * Using {{resultSet.isAfterLast()}} may not be a good idea because the support 
for that method is optional for {{TYPE_FORWARD_ONLY}} result sets.
 * Checking the {{resultSet}} is closed right after entering 
{{JdbcCommon.convertToAvroStream}} could work as a quick fix, but it would make 
the whole thing even harder to understand and maintain. Maybe some refactoring 
would be in order?

was (Author: msugar):
In QueryDatabaseTable.java, method onTrigger, line 278, a resultSet is created 
but not used to control the while loop two lines below. The resultSet is 
handled to another method, JdbcCommon.convertToAvroStream, which does its job 
and returns the number of rows it used to populate the output Avro file.

Since no other indication the last resultSet.next() returned false (and as a 
consequence the resultSet it's now closed) is passed back to 
QueryDatabaseTable, so it cannot know it should break out of the while loop and 
once again calls convertToAvroStream. This time the method throws an exception 
when trying to create the Schema (first line of JdbcCommon.convertToAvroStream, 
line 256).

Perhaps this logic works fine with other databases, but considering the 
resultSet was created without using try-with-resoruces and I couldn't find any 
explicit resultSet.close(), I'm wondering if the it would be left open or not.

Note: Using resultSet.isAfterLast() may not a good idea. It may be driver-, 
database-, or result-set-type dependent.

> QueryDatabaseTable throws SqlException after reading entire DB2 table
> ---------------------------------------------------------------------
>                 Key: NIFI-4926
>                 URL: https://issues.apache.org/jira/browse/NIFI-4926
>             Project: Apache NiFi
>          Issue Type: Bug
>          Components: Extensions
>    Affects Versions: 1.5.0
>         Environment: ubuntu 16.04
> nifi 1.5.0
> db2 v10.5.0.7
> JDBC driver db2jcc4-
>            Reporter: Marcio Sugar
>            Priority: Major
> I'm trying to replicate a table from one database to another using NiFi. My 
> flow is just a  QueryDatabaseTable connected to a PutDatabaseRecord. The 
> former fails with this SQLException after reading the whole table: 
> {code:java}
> 2018-03-02 15:20:44,688 INFO [NiFi Web Server-2017] 
> o.a.n.c.s.StandardProcessScheduler Starting 
> QueryDatabaseTable[id=e83d9370-0161-1000-d7d6-702ae791aaf1]
> 2018-03-02 15:20:44,692 INFO [StandardProcessScheduler Thread-2] 
> o.a.n.c.s.TimerDrivenSchedulingAgent Scheduled 
> QueryDatabaseTable[id=e83d9370-0161-1000-d7d6-702ae791aaf1] to run with 1 
> threads
> 2018-03-02 15:20:44,692 DEBUG [Timer-Driven Process Thread-2] 
> o.a.n.p.standard.QueryDatabaseTable 
> QueryDatabaseTable[id=e83d9370-0161-1000-d7d6-702ae791aaf1] Returning CLUSTER 
> State: StandardStateMap[version=54, values={}]
> 2018-03-02 15:20:44,693 DEBUG [Timer-Driven Process Thread-2] 
> o.a.n.p.standard.QueryDatabaseTable 
> QueryDatabaseTable[id=e83d9370-0161-1000-d7d6-702ae791aaf1] Executing query 
> 2018-03-02 15:20:45,159 INFO [Flow Service Tasks Thread-1] 
> o.a.nifi.controller.StandardFlowService Saved flow controller 
> org.apache.nifi.controller.FlowController@77b729c4 // Another save pending = 
> false
> 2018-03-02 15:21:41,577 INFO [Timer-Driven Process Thread-2] 
> o.a.n.p.standard.QueryDatabaseTable 
> QueryDatabaseTable[id=e83d9370-0161-1000-d7d6-702ae791aaf1] 
> StandardFlowFileRecord[uuid=fc5e66c0-14ef-4ed5-8d84-7c4d582000b7,claim=StandardContentClaim
>  [resourceClaim=StandardResourceClaim[id=1520022044698-4, container=default, 
> section=4], offset=0, 
> length=222061615],offset=0,name=264583001281149,size=222061615] contains 
> 652026 Avro records; transferring to 'success'
> 2018-03-02 15:21:41,578 ERROR [Timer-Driven Process Thread-2] 
> o.a.n.p.standard.QueryDatabaseTable 
> QueryDatabaseTable[id=e83d9370-0161-1000-d7d6-702ae791aaf1] Unable to execute 
> SQL select query SELECT * FROM FXSCHEMA.USER due to 
> org.apache.nifi.processor.exception.ProcessException: Error during database 
> query or conversion of records to Avro.: {}
> org.apache.nifi.processor.exception.ProcessException: Error during database 
> query or conversion of records to Avro.
> at 
> org.apache.nifi.processors.standard.QueryDatabaseTable.lambda$onTrigger$0(QueryDatabaseTable.java:291)
> at 
> org.apache.nifi.controller.repository.StandardProcessSession.write(StandardProcessSession.java:2571)
> at 
> org.apache.nifi.processors.standard.QueryDatabaseTable.onTrigger(QueryDatabaseTable.java:285)
> at 
> org.apache.nifi.controller.StandardProcessorNode.onTrigger(StandardProcessorNode.java:1122)
> at 
> org.apache.nifi.controller.tasks.ContinuallyRunProcessorTask.call(ContinuallyRunProcessorTask.java:147)
> at 
> org.apache.nifi.controller.tasks.ContinuallyRunProcessorTask.call(ContinuallyRunProcessorTask.java:47)
> at 
> org.apache.nifi.controller.scheduling.TimerDrivenSchedulingAgent$1.run(TimerDrivenSchedulingAgent.java:128)
> at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
> at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
> at 
> java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
> at 
> java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
> at 
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> at 
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> at java.lang.Thread.run(Thread.java:748)
> Caused by: com.ibm.db2.jcc.am.SqlException: [jcc][t4][10120][10898][4.19.26] 
> Invalid operation: result set is closed. ERRORCODE=-4470, SQLSTATE=null
> at com.ibm.db2.jcc.am.kd.a(Unknown Source)
> at com.ibm.db2.jcc.am.kd.a(Unknown Source)
> at com.ibm.db2.jcc.am.kd.a(Unknown Source)
> at com.ibm.db2.jcc.am.ResultSet.checkForClosedResultSet(Unknown Source)
> at com.ibm.db2.jcc.am.ResultSet.getMetaDataX(Unknown Source)
> at com.ibm.db2.jcc.am.ResultSet.getMetaData(Unknown Source)
> at 
> org.apache.commons.dbcp.DelegatingResultSet.getMetaData(DelegatingResultSet.java:322)
> at 
> org.apache.commons.dbcp.DelegatingResultSet.getMetaData(DelegatingResultSet.java:322)
> at 
> org.apache.nifi.processors.standard.util.JdbcCommon.createSchema(JdbcCommon.java:452)
> at 
> org.apache.nifi.processors.standard.util.JdbcCommon.convertToAvroStream(JdbcCommon.java:256)
> at 
> org.apache.nifi.processors.standard.QueryDatabaseTable.lambda$onTrigger$0(QueryDatabaseTable.java:289)
> ... 13 common frames omitted
> {code}
> According to [DB2's 
> documentation|http://www-01.ibm.com/support/docview.wss?uid=swg21461670], 
> this particular exception could be avoided by adding this setting (semicolon 
> included) to the JDBC connection URL:
> {code:java}
> allowNextOnExhaustedResultSet=1;{code}
> But it didn't make a difference.
> I also tried to set the 'Fetch Size' and 'Max Rows Per Flow File' to 
> different values, to no avail.
> Setting the 'Additional WHERE clause' to get just a small number of rows 
> didn't help either.
> It looks like the connection is been prematurely closed by the processor.

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