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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DERBY-5632) Logical deadlock happened when freezing/unfreezing the database
Date Wed, 19 Dec 2012 10:11:13 GMT

     [ https://issues.apache.org/jira/browse/DERBY-5632?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Knut Anders Hatlen updated DERBY-5632:

    Attachment: experimental-v2.diff

Attaching version 2 of the patch that removes the explicit synchronization on the conglomerate
cache. The only difference from version 1 is the way it retrieves a handle to the current
transaction from CacheableConglomerate.setIdentity(). Now it uses the nested transaction instead
of the top-level user transaction if there is one.

I wasn't quite happy with the approach used to get the current transaction (see RAMAccessManager.getCurrentTransactionContext())
as it needed to make some assumptions on how different transaction context types are stacked.
I think it should do the right thing, though.

Apart from that, I think the patch is an improvement, as it allows more concurrent access
to the conglomerate cache. Whether or not it helps with the deadlock, or if it just makes
it block on some other monitor, I don't know.
> 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: Documentation, Services
>    Affects Versions:
>         Environment: Oracle M3000/Solaris 10
>            Reporter: Brett Bergquist
>              Labels: derby_triage10_10
>         Attachments: experimental-v1.diff, experimental-v2.diff, 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
>                 - 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
>                 at org.apache.derby.impl.store.access.RAMTransaction.openGroupFetchScan(Unknown
>                 at org.apache.derby.impl.services.daemon.IndexStatisticsDaemonImpl.updateIndexStatsMinion(Unknown
>                 at org.apache.derby.impl.services.daemon.IndexStatisticsDaemonImpl.runExplicitly(Unknown
>                 at org.apache.derby.impl.sql.execute.AlterTableConstantAction.updateStatistics(Unknown
> 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
> 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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