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From "Tom Wilkie (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-3116) Compactions can (seriously )delay schema migrations
Date Thu, 01 Sep 2011 17:02:17 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-3116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13095416#comment-13095416
] 

Tom Wilkie commented on CASSANDRA-3116:
---------------------------------------

Its worse than this too; a migration tried to get the write lock, which gets blocked on a
big compaction (holding the read lock).  This migration waiting on the write lock then blocks
all other compactions waiting on the read lock.  So you only get one compaction going on and
thousands backing up.

A really hacky temporary fix would be to use a tryLock(timeout) and short sleep in a loop
in the migration.  This would at least not starve the merges, but would starve the migrations
quite badly.

> Compactions can (seriously )delay schema migrations
> ---------------------------------------------------
>
>                 Key: CASSANDRA-3116
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3116
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 0.8.4
>            Reporter: Eric Evans
>             Fix For: 1.1
>
>
> A compaction lock is acquired when dropping keyspaces or column families which will cause
the schema migration to block if a compaction is in progress.

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