[hibernate-dev] Missing transaction hangs the testsuite

Steve Ebersole steve at hibernate.org
Fri Jul 17 14:33:36 EDT 2015 

Here is something else interesting...

So at the point that the test hang against MySQL for me, I have:

MariaDB [(none)]> SHOW FULL processlist;
+-----+--------------------+-----------------+--------------------+---------+------+---------------------------------+--------------------------------+----------+
| Id  | User               | Host            | db                 | Command
| Time | State                           | Info                           |
Progress |
+-----+--------------------+-----------------+--------------------+---------+------+---------------------------------+--------------------------------+----------+
| 138 | root               | localhost       | NULL               | Query
|    0 | init                            | SHOW FULL processlist          |
   0.000 |
| 139 | hibernate_orm_test | localhost:52853 | hibernate_orm_test | Sleep
|   12 |                                 | NULL                           |
   0.000 |
| 140 | hibernate_orm_test | localhost:52854 | hibernate_orm_test | Query
|   12 | Waiting for table metadata lock | drop table if exists TheEntity |
   0.000 |
+-----+--------------------+-----------------+--------------------+---------+------+---------------------------------+--------------------------------+----------+

So we see 2 JDBC connections with process ids 139 and 140.  You can see 139
blocked waiting to be able to drop a table; specifically waiting on a lock
of some sort.

However, `SHOW OPEN TABLES;` shows no tables in use and no tables locked.

Unfortunately that is the extent of my "MySQL debugging skills".


On Fri, Jul 17, 2015 at 11:14 AM Steve Ebersole <steve at hibernate.org> wrote:

> Process != test.  Process here == connection.  You have multiple.
>
> On Fri, Jul 17, 2015, 11:12 AM Sanne Grinovero <sanne at hibernate.org>
> wrote:
>
>> On 17 July 2015 at 16:25, Steve Ebersole <steve at hibernate.org> wrote:
>> > It would seem that this is a regression with ORM, I agree.  However, we
>> do
>> > not know how recent of a regression.  And that is the problem.  We have
>> no
>> > idea how far back to look.  Because the ORM CI jobs against MySQL,
>> > PostrgreSQL, Oracle, etc have not been running for many months.  IIRC
>> even
>> > when they were running on the old CI servers we had problems with those
>> jobs
>> > that were not looked at for some time.
>>
>> Sure, same problem here: not run these tests for months, and you're
>> right I could do a quick check on a slightly older branch which is
>> using ORM 4.3 and I have the same problem.
>>
>> > As far as what you see, I am not convinced it is what you think it is in
>> > terms of auto-commit for queries run outside of a transaction.  This
>> part
>> > has not changed in 5.0.  Assuming you are using the "built in Connection
>> > pool", there is a setting that controls the auto-commit mode of the
>> > connections we create (hibernate.connection.autocommit).  That setting
>> has
>> > always been there, and it has always defaulted to false.  This has not
>> > changed.  In fact the same exact code is used in 4.3 and 5.0 for
>> creating
>> > these Connections:
>> > org.hibernate.engine.jdbc.connections.internal.BasicConnectionCreator.
>> The
>> > autoCommit value in there comes from the setting I just mentioned.  The
>> > logical outcome is the same even before 4.3, just that it was done
>> > differently.  So bottom line, if you are not seeing auto-commit on these
>> > Connections now, you never were.  Now it is possible that their are some
>> > ancillary changes that cause the lack of auto-commit to now be an issue
>> > where it was not before.  So first, I'd need to know whether the
>> Connection
>> > here is auto-commit or is not.  From there we can start drilling down on
>> > what might be a cause.  But keep in mind too, that with hangs and
>> deadlocks
>> > the process that hangs is often not the culprit; often it is the
>> previous
>> > process that is holding locks that is the culprit.
>>
>> I understand, but in this specific case I can reproduce the issue by
>> running a single test.
>> Also that psql SQL I shared clearly shows which statement is causing it
>> to hang,
>> and I could fix the test by just wrapping that statement in a transaction.
>>
>> >
>> > My case is actually different, at least on the surface.  Mine happens on
>> > dropping tables after the test is complete (for MySQL anyway).  Which
>> got me
>> > to looking at schema export and friends and how they handle connections.
>> > They handle connections quite differently.  Again the same as they used
>> to,
>> > but I mean very different from how sessions manage connections.  In
>> schema
>> > export the connections are always set to auto-commit mode at the start
>> of
>> > processing.  Then they never do anything with auto-commit afterwards.
>> I am
>> > not sure this is right.
>>
>> Actually it sounds like you're having the same problem. I debugged the
>> PosgreSQL tests first, but I had the same on MySQL (as in the
>> stacktrace I shared),
>> and the test also hangs on schema drop.
>> The problem is that the schema can't be dropped because a previous
>> statement - from a session which is now correctly closed - is still
>> holding locks.
>>
>> Thanks,
>> Sanne
>>
>> >
>> >
>> >
>> >
>> > On Fri, Jul 17, 2015 at 3:51 AM Sanne Grinovero <sanne at hibernate.org>
>> wrote:
>> >>
>> >> Thanks Steve, I wasn't sure if I had found a problem.
>> >> Still, it looks like the Hibernate Search tests are not benefiting
>> >> from auto-commit, or I wouldn't have this problem right? Our testing
>> >> configuration properties have been the same for years and I'm just
>> >> re-enabling tests which haven't been run for a while, so I suspect
>> >> something changed in ORM.
>> >>
>> >> I think I'd expect Hibernate ORM to automatically enable auto-commit
>> >> on operations not running within a transaction, to make sure all locks
>> >> are released when the Session is closed.
>> >>
>> >> Thanks,
>> >> Sanne
>> >>
>> >> On 17 July 2015 at 00:14, Steve Ebersole <steve at hibernate.org> wrote:
>> >> > For what it is worth, I am running into the same problems on MySQL
>> for
>> >> > the
>> >> > ORM tests in terms of blocks on dropping tables.  PGSQL at least
>> >> > finishes,
>> >> > although I run into 55 errors which I still need to triage.
>> >> >
>> >> > On Thu, Jul 16, 2015 at 5:59 PM Steve Ebersole <steve at hibernate.org>
>> >> > wrote:
>> >> >>
>> >> >> There is really nothing to improve.  What would you suggest as an
>> >> >> improvement?  I mean from a ORM perspective, we have an ato-commit
>> >> >> Connection (presumably) and run a query.  How on earth would we
>> know to
>> >> >> expect that the database is holding locks for that?
>> >> >>
>> >> >> As far as "requiring transactions" I have tried to fly that plane
>> >> >> multiple
>> >> >> times in the past.  I think it is absolutely ridiculous to allow
>> these
>> >> >> auto-commit use cases.  In fact I personally wanted to take it to
>> the
>> >> >> more
>> >> >> extreme case of always using JTA and simply mimicking "single
>> resource
>> >> >> JTA
>> >> >> transactions" internally in the "JDBC transaction" case.  Gavin and
>> I
>> >> >> both
>> >> >> did in fact.  But we got a lot of push back.
>> >> >>
>> >> >> So I am not sure exactly what the improvement here might be.  What
>> is
>> >> >> it
>> >> >> you were thinking specifically?
>> >> >>
>> >> >> On Thu, Jul 16, 2015 at 5:36 PM Sanne Grinovero <
>> sanne at hibernate.org>
>> >>
>> >> >> wrote:
>> >> >>>
>> >> >>> I finally got to re-enable MariaDB and PostgreSQL based tests for
>> >> >>> Hibernate Search - which has been running on H2 only for some
>> months -
>> >> >>> and had to debug a case of a single test hanging for a long time.
>> >> >>>
>> >> >>> Essentially it would block - for hours - on the
>> SessionFactory#close()
>> >> >>> method, attempting to drop the database schema with the following
>> >> >>> statement:
>> >> >>>   > alter table AncientBook_alternativeTitles drop constraint
>> >> >>> FKn8hhkmhof1mdgc4oi77ccq989
>> >> >>>
>> >> >>> Dumping threads I would get a very similar stack trace on both
>> >> >>> databases; initially I thought someone had copy/pasted a socket
>> >> >>> handling bug from one JDBC driver to the other ;-)
>> >> >>>
>> >> >>> The PostgreSQL testsuite hanging:
>> >> >>>
>> >> >>> "main" prio=10 tid=0x00007f0f40009000 nid=0x5f7c runnable
>> >> >>> [0x00007f0f48956000]
>> >> >>>    java.lang.Thread.State: RUNNABLE
>> >> >>> at java.net.SocketInputStream.socketRead0(Native Method)
>> >> >>> at java.net.SocketInputStream.read(SocketInputStream.java:152)
>> >> >>> at java.net.SocketInputStream.read(SocketInputStream.java:122)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.postgresql.core.VisibleBufferedInputStream.readMore(VisibleBufferedInputStream.java:145)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.postgresql.core.VisibleBufferedInputStream.ensureBytes(VisibleBufferedInputStream.java:114)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.postgresql.core.VisibleBufferedInputStream.read(VisibleBufferedInputStream.java:73)
>> >> >>> at org.postgresql.core.PGStream.ReceiveChar(PGStream.java:274)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1660)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:257)
>> >> >>> - locked <0x00000007c11e3860> (a
>> >> >>> org.postgresql.core.v3.QueryExecutorImpl)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:500)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:374)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.postgresql.jdbc2.AbstractJdbc2Statement.executeUpdate(AbstractJdbc2Statement.java:302)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.hibernate.tool.hbm2ddl.DatabaseExporter.export(DatabaseExporter.java:47)
>> >> >>> at
>> >> >>>
>> org.hibernate.tool.hbm2ddl.SchemaExport.perform(SchemaExport.java:476)
>> >> >>> at
>> >> >>>
>> org.hibernate.tool.hbm2ddl.SchemaExport.execute(SchemaExport.java:430)
>> >> >>> at
>> org.hibernate.tool.hbm2ddl.SchemaExport.drop(SchemaExport.java:375)
>> >> >>> at
>> org.hibernate.tool.hbm2ddl.SchemaExport.drop(SchemaExport.java:371)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.hibernate.internal.SessionFactoryImpl.close(SessionFactoryImpl.java:1069)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.hibernate.search.test.util.FullTextSessionBuilder.close(FullTextSessionBuilder.java:149)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.hibernate.search.test.util.FullTextSessionBuilder$1.evaluate(FullTextSessionBuilder.java:248)
>> >> >>> at org.junit.rules.RunRules.evaluate(RunRules.java:20)
>> >> >>> at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:264)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:153)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:124)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.apache.maven.surefire.booter.ForkedBooter.invokeProviderInSameClassLoader(ForkedBooter.java:200)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:153)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:103)
>> >> >>>
>> >> >>> The MariaDB testsuite hanging:
>> >> >>>
>> >> >>> "main" prio=10 tid=0x00007f8ca0009000 nid=0x4043 runnable
>> >> >>> [0x00007f8ca5f5c000]
>> >> >>>    java.lang.Thread.State: RUNNABLE
>> >> >>> at java.net.SocketInputStream.socketRead0(Native Method)
>> >> >>> at java.net.SocketInputStream.read(SocketInputStream.java:152)
>> >> >>> at java.net.SocketInputStream.read(SocketInputStream.java:122)
>> >> >>> at
>> >> >>>
>> >> >>>
>> com.mysql.jdbc.util.ReadAheadInputStream.fill(ReadAheadInputStream.java:114)
>> >> >>> at
>> >> >>>
>> >> >>>
>> com.mysql.jdbc.util.ReadAheadInputStream.readFromUnderlyingStreamIfNecessary(ReadAheadInputStream.java:161)
>> >> >>> at
>> >> >>>
>> >> >>>
>> com.mysql.jdbc.util.ReadAheadInputStream.read(ReadAheadInputStream.java:189)
>> >> >>> - locked <0x00000007c0baa518> (a
>> >> >>> com.mysql.jdbc.util.ReadAheadInputStream)
>> >> >>> at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2499)
>> >> >>> at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2952)
>> >> >>> at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2941)
>> >> >>> at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3489)
>> >> >>> at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1959)
>> >> >>> at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2113)
>> >> >>> at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2562)
>> >> >>> - locked <0x00000007c0baa850> (a java.lang.Object)
>> >> >>> at
>> com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1664)
>> >> >>> - locked <0x00000007c0baa850> (a java.lang.Object)
>> >> >>> at
>> com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1583)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.hibernate.tool.hbm2ddl.DatabaseExporter.export(DatabaseExporter.java:47)
>> >> >>> at
>> >> >>>
>> org.hibernate.tool.hbm2ddl.SchemaExport.perform(SchemaExport.java:476)
>> >> >>> at
>> >> >>>
>> org.hibernate.tool.hbm2ddl.SchemaExport.execute(SchemaExport.java:430)
>> >> >>> at
>> org.hibernate.tool.hbm2ddl.SchemaExport.drop(SchemaExport.java:375)
>> >> >>> at
>> org.hibernate.tool.hbm2ddl.SchemaExport.drop(SchemaExport.java:371)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.hibernate.internal.SessionFactoryImpl.close(SessionFactoryImpl.java:1069)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.hibernate.search.test.util.FullTextSessionBuilder.close(FullTextSessionBuilder.java:149)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.hibernate.search.test.util.FullTextSessionBuilder$1.evaluate(FullTextSessionBuilder.java:248)
>> >> >>> at org.junit.rules.RunRules.evaluate(RunRules.java:20)
>> >> >>> at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:264)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:153)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:124)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.apache.maven.surefire.booter.ForkedBooter.invokeProviderInSameClassLoader(ForkedBooter.java:200)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:153)
>> >> >>> at
>> >> >>>
>> >> >>>
>> org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:103)
>> >> >>>
>> >> >>> On Gail's suggestion I went looking for database level locks; I
>> hadn't
>> >> >>> thought of that as I assumed it would have timed out more
>> aggressively
>> >> >>> rather than have me wait for hours.
>> >> >>> It turns out she was right and the reason for blocking was a simple
>> >> >>> "count *" query being run as a post-test assertion, which we had
>> >> >>> forgotten to wrap in an "open transaction & commit" statements
>> pair.
>> >> >>> The test assertion would be successful, but apparently it would
>> hold
>> >> >>> on the table lock beyond closing the Session and, then fail to drop
>> >> >>> the database at the teardown of the test.
>> >> >>>
>> >> >>> I'm wondering if this is expected, or if there's something in the
>> new
>> >> >>> transaction handling code which could be improved? It took me
>> several
>> >> >>> hours to figure this out; maybe I'm just not using ORM as
>> frequently
>> >> >>> as once :)
>> >> >>> If it's this critical to have the transaction, maybe it should be
>> >> >>> mandatory?
>> >> >>>
>> >> >>> And as a memo for next time, this is the query to figure out
>> details
>> >> >>> about locks on our testing db:
>> >> >>>  > SELECT * FROM pg_locks pl LEFT JOIN pg_stat_activity psa ON
>> pl.pid
>> >> >>> = psa.pid where datname = 'testingdb';
>> >> >>>
>> >> >>> Thanks,
>> >> >>> Sanne
>> >> >>> _______________________________________________
>> >> >>> hibernate-dev mailing list
>> >> >>> hibernate-dev at lists.jboss.org
>> >> >>> https://lists.jboss.org/mailman/listinfo/hibernate-dev
>>
>

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