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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Ticket CASSANDRA-3578 - Multithreaded CommitLog
Date Thu, 08 Dec 2011 07:40:57 GMT
2011/12/8 Piotr Kołaczkowski <pkolaczk@ii.pw.edu.pl>:
> Right, this would be the best option to have an ability to write into
> multiple log files, put on multiple disks. I'm not sure if it is part of
> that ticket, though.

It's not.  I don't think anyone needs more than 80MB/s or so of
commitlog bandwidth for a while.

> BTW: I'm not so sure if multiple, parallel writes to a memory mapped file
> would be actually slower or faster than sequential writes. I think the OS
> would optimise the writes so that physically they would be sequential, or
> even delay them until fsync (or low cached disk buffers), so no performance
> loss would occur

Right.  What we're trying to fix here is having a single thread doing
the copying + checksumming being a bottleneck.  The i/o pattern should
stay more or less the same.

-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com

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