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https://issues.apache.org/jira/browse/DERBY-5632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13217796#comment-13217796
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Brett Bergquist commented on DERBY-5632:
----------------------------------------
I don't think it is clear that one MUST use the same connection. To me that
is an example of how one MIGHT do the backup. In any case, I could do it as
suggested by invoking a system command from within a Java utility but my fear
is as you suggested, what happens if the utility fails before performing an
unfreeze? Having to kill the network server is really not a good answer.
The 3 separate steps as I mentioned does in fact work frequently. I ran it a
bunch of other times with no problems, but unfortunately (or maybe
fortunately), it failed for me the very first time I tried it.
So if one were to do it within one connection, I think that maybe if the
connection is lost, then an unfreeze is done automatically to ensure not being
locked out of the network server.
> Logical deadlock happened when freezing/unfreezing the database
> ---------------------------------------------------------------
>
> Key: DERBY-5632
> URL: https://issues.apache.org/jira/browse/DERBY-5632
> Project: Derby
> Issue Type: Bug
> Components: Network Server
> Affects Versions: 10.8.2.2
> Environment: Oracle M3000/Solaris 10
> Reporter: Brett Bergquist
> Attachments: stack.txt
>
>
> Tried to make a quick database backup by freezing the database, performing a
> ZFS snapshot, and then unfreezing the database. The database was frozen but
> then a connection to the database could not be established to unfreeze the
> database.
> Looking at the stack trace of the network server, , I see 3 threads that are
> trying to process a connection request. Each of these is waiting on:
> at
> org.apache.derby.impl.store.access.RAMAccessManager.conglomCacheFind(Unknown
> Source)
> - waiting to lock <0xfffffffd3a7fcc68> (a
> org.apache.derby.impl.services.cache.ConcurrentCache)
> That object is owned by:
> - locked <0xfffffffd3a7fcc68> (a
> org.apache.derby.impl.services.cache.ConcurrentCache)
> at
> org.apache.derby.impl.store.access.RAMTransaction.findExistingConglomerate(Unknown
> Source)
> at
> org.apache.derby.impl.store.access.RAMTransaction.openGroupFetchScan(Unknown
> Source)
> at
> org.apache.derby.impl.services.daemon.IndexStatisticsDaemonImpl.updateIndexStatsMinion(Unknown
> Source)
> at
> org.apache.derby.impl.services.daemon.IndexStatisticsDaemonImpl.runExplicitly(Unknown
> Source)
> at
> org.apache.derby.impl.sql.execute.AlterTableConstantAction.updateStatistics(Unknown
> Source)
> which itself is waiting for the object:
> at java.lang.Object.wait(Native Method)
> - waiting on <0xfffffffd3ac1d608> (a
> org.apache.derby.impl.store.raw.log.LogToFile)
> at java.lang.Object.wait(Object.java:485)
> at
> org.apache.derby.impl.store.raw.log.LogToFile.flush(Unknown Source)
> - locked <0xfffffffd3ac1d608> (a
> org.apache.derby.impl.store.raw.log.LogToFile)
> at
> org.apache.derby.impl.store.raw.log.LogToFile.flush(Unknown Source)
> at
> org.apache.derby.impl.store.raw.data.BaseDataFileFactory.flush(Unknown Source)
> So basically what I think is happening is that the database is frozen, the
> statistics are being updated on another thread which has the
> "org.apache.derby.impl.services.cache.ConcurrentCache" locked and then waits
> for the LogToFile lock and the connecting threads are waiting to lock
> "org.apache.derby.impl.services.cache.ConcurrentCache" to connect and these
> are where the database is going to be unfrozen. Not a deadlock as far as
> the JVM is concerned but it will never leave this state either.
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