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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3130) Reduce memory footprint of StoredRecordHeader
Date Mon, 15 Oct 2007 18:03:50 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3130?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12534918
] 

Knut Anders Hatlen commented on DERBY-3130:
-------------------------------------------

A StoredRecordHeader object is created the first time its corresponding record is accessed
after a page has been fetched into the page cache. When a page is evicted from the cache,
all its StoredRecordHeader objects can be gc'ed. The number 136814 means that there are 1000
pages, on each of which 136.8 records have been accessed.

> Reduce memory footprint of StoredRecordHeader
> ---------------------------------------------
>
>                 Key: DERBY-3130
>                 URL: https://issues.apache.org/jira/browse/DERBY-3130
>             Project: Derby
>          Issue Type: Improvement
>          Components: Store
>    Affects Versions: 10.4.0.0
>            Reporter: Knut Anders Hatlen
>            Priority: Minor
>         Attachments: SmallRecordsTest.java, srh.diff
>
>
> Derby's page cache often has a memory footprint that is much larger than pageSize*pageCacheSize.
One large contributor to the footprint is the array of StoredPageHeader objects in BasePage.
The memory consumed by these objects can be as large as, and sometimes even larger than, the
byte arrays containing the raw page data. (See for instance http://www.nabble.com/How-much-derby-need-memory--tf3307655.html.)
Reducing the size of the StoredPageHeader objects could therefore reduce Derby's memory footprint
significantly, especially if the page cache is large and contains many pages from tables with
small records or from indices.

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