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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2020) Change file option for syncing log file to disk from rws to rwd
Date Sun, 25 Mar 2007 07:14:32 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2020?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12483911

Knut Anders Hatlen commented on DERBY-2020:

Hi Olav,

I think your approach of moving the checking into a separate method run on boot is good. However,
I see two problems with checkJvmSyncError().

  1) By opening the temporary file in rw mode first, you will make sure it exists. When the
file exists, opening it in rws mode doesn't fail, so the bug will go undetected.
  2) When opening the temp file in rws mode, you check for IOException. The bug will always
cause a FileNotFoundException, so it's better to check for that exact exception so that other
(unexpected) IOExceptions are not swallowed/misinterpreted.

> Change file option for syncing log file to disk from rws to rwd
> ---------------------------------------------------------------
>                 Key: DERBY-2020
>                 URL: https://issues.apache.org/jira/browse/DERBY-2020
>             Project: Derby
>          Issue Type: Improvement
>          Components: Performance, Store
>    Affects Versions:
>            Reporter: Olav Sandstaa
>         Assigned To: Olav Sandstaa
>         Attachments: disk-cache.png, jvmsyncbug.diff, jvmsyncbug.stat, no-disk-cache.png,
rwd.diff, rwd.stat
> 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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