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https://issues.apache.org/jira/browse/DERBY-7015?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17013859#comment-17013859
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Richard N. Hillegas commented on DERBY-7015:
--------------------------------------------
The DatabaseMetaData methods run queries against the SYS.SYS* tables. That is,
they do not rely on the DataDictionary's in-memory metadata cache. I am,
however, suprised that a DatabaseMetaData query would deadlock against another
instance of itself. Might there be another thread which issues DDL at the same
time?
> DatabaseMetaData.getTables gives exception when called from two threads and
> the statement is stale
> --------------------------------------------------------------------------------------------------
>
> Key: DERBY-7015
> URL: https://issues.apache.org/jira/browse/DERBY-7015
> Project: Derby
> Issue Type: Bug
> Components: JDBC
> Affects Versions: 10.14.2.0
> Environment: Linux amd64
> Reporter: Alex
> Priority: Minor
> Attachments: DerbyGetTablesDeadlockTest.java, exception-reported.txt,
> threads-during-hang.txt
>
>
> In certain circumstances, when two threads both call
> DatabaseMetaData.getTables at the same time, one fails with the exception "A
> lock could not be obtained within the time requested".
> This seems to be when the statement has been executed 100 times (I think as
> per derby.language.stalePlanCheckInterval) and the number of rows returned by
> the query is different compared to the first time getTables was called.
> I attach a test case which reproduces the problem on my workstation most
> times I execute it.
> Output from java org.apache.derby.tools.sysinfo:
> {noformat}
> ------------------ Java Information ------------------
> Java Version: 1.8.0_66
> Java Vendor: Oracle Corporation
> Java home: /home/myuser/bin/local/jdk1.8.0_66/jre
> Java classpath:
> /home/myuser/workspace/DerbyDemo/bin:/home/myuser/workspace/DerbyDemo/lib/derby.jar:/home/myuser/workspace/DerbyDemo/lib/junit-4.11.jar:/home/myuser/workspace/DerbyDemo/lib/hamcrest-core-1.3.jar
> OS name: Linux
> OS architecture: amd64
> OS version: 4.4.0-134-generic
> Java user name: myuser
> Java user home: /home/myuser
> Java user dir: /home/myuser/workspace/DerbyDemo
> java.specification.name: Java Platform API Specification
> java.specification.version: 1.8
> java.runtime.version: 1.8.0_66-b17
> --------- Derby Information --------
> [/home/myuser/workspace/DerbyDemo/lib/derby.jar] 10.14.2.0 - (1828579)
> ------------------------------------------------------
> ----------------- Locale Information -----------------
> ------------------------------------------------------
> ------------------------------------------------------{noformat}
> Also attached is the exception that it produces, and also a jstack of the two
> threads when everything is hung but before the exception is thrown.
>
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