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From "Dag H. Wanvik (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-704) Large page cache kills initial performance
Date Mon, 29 Jun 2009 14:45:47 GMT

     [ https://issues.apache.org/jira/browse/DERBY-704?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Dag H. Wanvik updated DERBY-704:
--------------------------------

    Derby Categories: [Performance]

> Large page cache kills initial performance
> ------------------------------------------
>
>                 Key: DERBY-704
>                 URL: https://issues.apache.org/jira/browse/DERBY-704
>             Project: Derby
>          Issue Type: Bug
>          Components: Services
>    Affects Versions: 10.1.1.0, 10.1.2.1, 10.1.3.1, 10.2.1.6
>         Environment: All platforms
>            Reporter: Knut Anders Hatlen
>            Assignee: Knut Anders Hatlen
>             Fix For: 10.1.3.1, 10.2.1.6
>
>         Attachments: cpu-usage.png, DERBY-704-extra-comments.diff, DERBY-704.diff, derbyall_report.txt,
throughput.png
>
>
> When the page cache is large the performance gets lower as the page
> cache is being filled. As soon as the page cache is filled, the
> throughput increases. In the period with low performance, the CPU
> usage is high, and when the performance increases the CPU usage is
> lower.
> This behaviour is caused by the algorithm for finding free slots in
> the page cache. If there are invalid pages in the page cache, it will
> be scanned to find one of those pages. However, when multiple clients
> access the database, the invalid pages are often already taken. This
> means that the entire page cache will be scanned, but no free invalid
> page is found. Since the scan of the page cache is synchronized on the
> cache manager, all other threads that want to access the page cache
> have to wait. When the page cache is large, this will kill the
> performance.
> When the page cache is full, this is not a problem, as there will be
> no invalid pages.

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