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From "Ferdy Galema (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (GORA-84) SqlStore not thread-safe because of Closed Statements
Date Mon, 23 Jan 2012 10:56:41 GMT

    [ https://issues.apache.org/jira/browse/GORA-84?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13191107#comment-13191107

Ferdy Galema commented on GORA-84:

We can put this issue on hold until the set of libraries is updated and well. Perhaps this
issue will be superseded in the process.
> SqlStore not thread-safe because of Closed Statements
> -----------------------------------------------------
>                 Key: GORA-84
>                 URL: https://issues.apache.org/jira/browse/GORA-84
>             Project: Gora
>          Issue Type: Bug
>          Components: storage-sql
>            Reporter: Ferdy Galema
> In some multithreaded test code (actually Nutchgora TestGoraStorage) the current trunk
of Gora SqlStore fails because of Closed Statements:
> Caused by: java.sql.SQLException: statement is closed
> 	at org.hsqldb.jdbc.Util.sqlException(Unknown Source)
> 	at org.hsqldb.jdbc.JDBCPreparedStatement.executeBatch(Unknown Source)
> 	at org.apache.gora.sql.store.SqlStore.flush(SqlStore.java:329)
> 	... 9 more
> Caused by: org.hsqldb.HsqlException: statement is closed
> 	at org.hsqldb.error.Error.error(Unknown Source)
> 	at org.hsqldb.error.Error.error(Unknown Source)
> 	at org.hsqldb.Session.executeCompiledBatchStatement(Unknown Source)
> 	at org.hsqldb.Session.execute(Unknown Source)
> 	... 11 more
> I am not sure why this problem suddenly arises as I could not find relevant changes in
the SqlStore related code. 
> The problem is caused of incorrectly synchronized code when buffering and flushing put
requests. Some statements are accidently shared between threads because of the shared write
buffer (the HashSet writeCache). So it may happen that some closed statements are trying to
be executed, raising the above exception. When I disabled SqlUtils.close() by making the method
empty, the tests worked again. So that is the lazy man's solution: Disable the writeCache.

> I suggest that somebody who is more into maintaining this store fixes it user a better
solution (proper synchronization). When there is no interest in doing so, I can still always
implement the lazy man's solution :)
> By the way, the fact that this error was not detected in Gora's own tests suggests that
we might want to expand it's coverage. This is in line what was already mentioned a few days
ago on the dev list ("inconsistencies in TestXXXStore").

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