[jira] Updated: (DERBY-2020) Change file option for syncing log file to disk from rws to rwd

["Olav Sandstaa (JIRA)" <ji...@apache.org>]

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

Olav Sandstaa updated DERBY-2020:
---------------------------------

    Attachment: jvmsyncbug_v3.stat
                jvmsyncbug_v3.diff

This patch includes changes based on comments from Suresh. The check for the JVM bug is now done in openLogFileInWriteMode. The test will be done on the log file that is going to be used. The check does first open the file in "rw" mode to ensure that the file exists and then re-opens it in "rws" mode. If a FileNotFoundExceptions is thrown, Derby will switch from using "write sync" mode to doing explicite syncing. The test is only done once when the first log file is opened in rws mode.

This patch does no change to the rws mode used by the log file writing.

I have run derbyall and the JUnit suite with no errors on Solaris 10. The patch is ready for review and commit.

> 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: 10.3.0.0
>            Reporter: Olav Sandstaa
>         Assigned To: Olav Sandstaa
>         Attachments: disk-cache.png, jvmsyncbug.diff, jvmsyncbug.stat, jvmsyncbug_v2.diff, jvmsyncbug_v2.stat, jvmsyncbug_v3.diff, jvmsyncbug_v3.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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