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From "Keith Turner (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-624) iterators may open lots of compressors
Date Thu, 21 Jun 2012 19:16:42 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-624?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13398761#comment-13398761
] 

Keith Turner commented on ACCUMULO-624:
---------------------------------------

The experiment I did was the following :

 * Edit conf/generic_logger.xml and set org.apache.accumulo.core.file.rfile.bcfile to DEBUG
 * Start tservers
 * Look at shard example and run the query command (after indexing)
 * Look at tserver logs, should see messages about allocating and deallocting multiple decompressors
 * Enable block cache on shard table
 * Major compact table or wait a few minutes for file to close, file open by previous query
does not have cache set
 * run shard example query again
 * look at tservers logs, should only see one decompressor used
 * subsequent queries may not show any decompressor use because data is cached

                
> iterators may open lots of compressors
> --------------------------------------
>
>                 Key: ACCUMULO-624
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-624
>             Project: Accumulo
>          Issue Type: Bug
>          Components: tserver
>            Reporter: Eric Newton
>            Assignee: Keith Turner
>
> A large iterator tree may create many instances of Compressors.  These instances are
pulled from a pool that never decreases in size.  So, if 50 simultaneous queries are run over
dozens of files, each with a complex iterator stack, there will be thousands of compressors
created.  Each of these holds a large buffer.  This can cause the server to run out of memory.

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