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From "Olav Sandstaa (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2020) Change file option for syncing log file to disk from rws to rwd
Date Fri, 03 Nov 2006 14:36:17 GMT
    [ http://issues.apache.org/jira/browse/DERBY-2020?page=comments#action_12446971 ] 
            
Olav Sandstaa commented on DERBY-2020:
--------------------------------------

I agree that it would be good to get a clarification of this into the specification. I will
try to discuss this with someone working in Sun's Java team and possibly enter a bug or a
request for improvement for this. Still, I think it is good to have some data from different
OSes on how this affect the performance in order to decide if this is worth the effort to
try to change how the log is written.

> Change file option for syncing log file to disk from rws to rwd
> ---------------------------------------------------------------
>
>                 Key: DERBY-2020
>                 URL: http://issues.apache.org/jira/browse/DERBY-2020
>             Project: Derby
>          Issue Type: Improvement
>          Components: Performance, Store
>    Affects Versions: 10.3.0.0
>            Reporter: Olav Sandstaa
>         Attachments: disk-cache.png, no-disk-cache.png
>
>
> For writing the transaction log to disk Derby uses a
> RandomAccessFile. If it is supported by the JVM, the log files are
> opened in "rws" mode making the file system take care of syncing
> writes to disk. "rws" mode will ensure that both the data and the file
> meta-data is updated for every write to the file. On some operating
> systems (e.g. Solaris) this leads to two write operation to the disk
> for every write issued by Derby. This is limiting the throughput of
> update intensive applications.  If we could change the file mode to
> "rwd" this could reduce the number of updates to the disk.
> I have run some simple tests where I have changed mode from "rws" to
> "rwd" for the Derby log file. When running a small numbers of
> concurrent client threads the throughput is almost doubled and the
> response time is almost halved. I will attach some graphs that show
> this when running a given number of concurrent "tpc-b" like clients. These
> graphs show the throughput when running with "rws" and "rwd" mode when the
> disk's write cache has been enabled and disabled.
> I am creating this Jira to have a place where we can collect
> information about issues both for and against changing the default
> mode for writing to log files.

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