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https://issues.apache.org/jira/browse/DERBY-1947?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12490311
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Knut Anders Hatlen commented on DERBY-1947:
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> Presumably the failure happens because the finalizers can't complete
> when gc() and runFinalization() is called, barring the
> result sets from being garbage collected as well.
It could also be that gc() just makes the garbage collection start, possibly in
another thread, so that runFinalization() is called before the objects are
marked as unreferenced. IIRC, gc() doesn't block whereas runFinalization() does.
Note that the IBM 1.5 VM implemented a much more aggressive gc than previous
versions. I remember that many tests had to be rewritten when people started
running tests with that VM because ResultSets were closed earlier, etc. That
probably explains why you don't see the deadlock in runFinalization() on IBM
1.5, since the objects most likely are gc'ed and finalized before you come to
that point.
> OutOfMemoryError after repeated calls to boot and shutdown a database
> ---------------------------------------------------------------------
>
> Key: DERBY-1947
> URL: https://issues.apache.org/jira/browse/DERBY-1947
> Project: Derby
> Issue Type: Bug
> Components: Services
> Affects Versions: 10.0.2.0, 10.0.2.1, 10.1.1.0, 10.1.2.1, 10.1.3.1,
> 10.2.1.6
> Environment: Any
> Reporter: Rajesh Kartha
> Assigned To: Dag H. Wanvik
> Attachments: DERBY-1947-1.diff, DERBY-1947-1.stat, DERBY-1947-2.diff,
> DERBY-1947-2.stat, DERBY-1947-3.diff, DERBY-1947-3.stat, HeapAnalysis_op.jpg,
> ProcedureInTriggerTest-threadstacks.txt, testEmbedAndClient.java
>
>
> I came across this OOM issue while running some system tests involving
> backup and restore against Derby. The test is expected to run forever but
> using the default heap space it runs into OOM within 2 days. I earlier
> mentioned about this
> in my reply to the 10.2.1.6 vote -
> http://www.nabble.com/Re%3A--VOTE--10.2.1.6-release-p6650528.html
> Also there has been some discussions on the list on the related topic:
> http://issues.apache.org/jira/browse/DERBY-23 and
> http://www.nabble.com/question-about-shutdown-tf2300504.html
> Basic Analysis:
> --------------------
> Wrote a simple Java app (attached to this issue) that booted and shutdown the
> same
> database multiple times. Depending on the heapsize the program ran into the
> OOM at some point, as expected. Some heap dump analysis using the IBM
> HeapAnalyzer
> and revealed that the HashSet (allContexts) within
> org.apache.derby.iapi.services.context.ContextService
> class seemed to be location of the leak (snapshot of the heapanalysis
> attached).
> A little bit of debugging shows that:
> - for every:connection two ContextManager objects (say, cm1, cm2) are added
> to the HashSet
> - for every shutdown a new ContextManager object (say, cm3) is added and two
> objects are removed
> - the object removed are cm2 and cm3 - in that sequence
> - but the object cm1 gets left behind
> This happens for every connect/shutdown sequence and since one of the
> ContextManager objects added to the
> HashSet is not removed as a part of the cleanup, it contributes to growth in
> memory usage, hence
> an OOM eventually.
> For example:
> ============
> A 64M heap could allow about 1107 iterations of connect/shutdown only before
> running into OOM and
> created 1108 un-used ContextManager objects in the memory.
> java -Xmx64M testEmbedAndClient
> ++++Debug: add() Size of allContexts HashSet obj= 1
> ----Debug: remove() Size of allContexts HashSet obj= 0
> ++++Debug: add() Size of allContexts HashSet obj= 1
> ----Debug: remove() Size of allContexts HashSet obj= 0
> ++++Debug: add() Size of allContexts HashSet obj= 1
> ++++Debug: add() Size of allContexts HashSet obj= 2
> ==== Database booted in embedded ====
> ++++Debug: add() Size of allContexts HashSet obj= 3
> ----Debug: remove() Size of allContexts HashSet obj= 2
> ----Debug: remove() Size of allContexts HashSet obj= 1
> ==== Shutdown complete in embedded ====
> ++++Debug: add() Size of allContexts HashSet obj= 2
> ++++Debug: add() Size of allContexts HashSet obj= 3
> ==== Database booted in embedded ====
> ++++Debug: add() Size of allContexts HashSet obj= 4
> ----Debug: remove() Size of allContexts HashSet obj= 3
> ----Debug: remove() Size of allContexts HashSet obj= 2
> ..
> ..
> ..
> ==== Database booted in embedded ====
> ++++Debug: add() Size of allContexts HashSet obj= 1109
> ----Debug: remove() Size of allContexts HashSet obj= 1108
> ----Debug: remove() Size of allContexts HashSet obj= 1107
> ==== Shutdown complete in embedded ====
> ++++Debug: add() Size of allContexts HashSet obj= 1108
> ++++Debug: add() Size of allContexts HashSet obj= 1109
> ----Debug: remove() Size of allContexts HashSet obj= 1108
> java.sql.SQLException: Failed to start database 'testdb', see the next
> exception
> for details.
> at
> org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(SQLExceptionFactory.java:45)
> at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Util.java:89)
> at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Util.java:95)
> at
> org.apache.derby.impl.jdbc.Util.generateCsSQLException(Util.java:174)
> at
> org.apache.derby.impl.jdbc.EmbedConnection.newSQLException(EmbedConnection.java:1985)
> at
> org.apache.derby.impl.jdbc.EmbedConnection.bootDatabase(EmbedConnection.java:1649)
> at
> org.apache.derby.impl.jdbc.EmbedConnection.<init>(EmbedConnection.java:223)
> at
> org.apache.derby.impl.jdbc.EmbedConnection30.<init>(EmbedConnection30.java:73)
> at
> org.apache.derby.jdbc.Driver30.getNewEmbedConnection(Driver30.java:74)
> at
> org.apache.derby.jdbc.InternalDriver.connect(InternalDriver.java:210)
> ----Debug: remove() Size of allContexts HashSet obj= 1107
> at
> org.apache.derby.jdbc.AutoloadedDriver.connect(AutoloadedDriver.java:117)
> at java.sql.DriverManager.getConnection(DriverManager.java:525)
> at java.sql.DriverManager.getConnection(DriverManager.java:193)
> at testEmbedAndClient.testInEmbedded(testEmbedAndClient.java:40)
> at testEmbedAndClient.main(testEmbedAndClient.java:19)
> java.lang.OutOfMemoryError: Java heap space
> OOM happened after 1107 iterations
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