Mailing-List: contact commits-help@cassandra.apache.org; run by ezmlm
Precedence: bulk
Reply-To: dev@cassandra.apache.org
Date: Mon, 21 Feb 2011 12:11:38 +0000 (UTC)
From: "Sylvain Lebresne (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: 
 <1291040486.5650.1298290298469.JavaMail.tomcat@hel.zones.apache.org>
In-Reply-To: <5613170.226211294457745232.JavaMail.jira@thor>
Subject: [jira] Commented: (CASSANDRA-1954) Double-check or replace RRW
 memtable lock
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit


    [ https://issues.apache.org/jira/browse/CASSANDRA-1954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12997369#comment-12997369 ] 

Sylvain Lebresne commented on CASSANDRA-1954:
---------------------------------------------

I agree with the change of frozen to pendingFlush, as well as that this should probably go to trunk (given it's in a fairly critical path).

> Double-check or replace RRW memtable lock
> -----------------------------------------
>
>                 Key: CASSANDRA-1954
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1954
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Stu Hood
>            Priority: Minor
>         Attachments: 0001-Double-check-in-maybeSwitchMemtable-to-minimize-writeL.txt, 0001-Remove-flusherLock-readLock.patch, 1954-v2.txt
>
>
> {quote}...when a Memtable reaches its threshold, up to (all) N write threads will often notice, and race to acquire the writeLock in order to freeze the memtable. This means that we do way more writeLock acquisitions than we need to...{quote}
> See CASSANDRA-1930 for backstory, but adding double checking inside a read lock before trying to re-entrantly acquire the writelock would eliminate most of these excess writelock acquisitions.
> Alternatively, we should explore removing locking from these structures entirely, and replacing the writeLock acquisition with a per-memtable counter of active threads.

-- 
This message is automatically generated by JIRA.
-
For more information on JIRA, see: http://www.atlassian.com/software/jira