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https://issues.apache.org/jira/browse/DERBY-3130?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Knut Anders Hatlen updated DERBY-3130:
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Attachment: SmallRecordsTest.java
Attached is a test which fills a table with 500000 small records (consisting of
a single int) and than waits for the user to press enter before it finishes.
With a default sized page cache (4000 pages), this is what jmap -histo:live
says about the contents of the heap when all the records have been inserted
(Sun Java 6, 32-bit):
num #instances #bytes class name
--------------------------------------
1: 136814 6567072
org.apache.derby.impl.store.raw.data.StoredRecordHeader
2: 5239 4568104 [B
3: 14465 1447800 <constMethodKlass>
4: 14465 1158248 <methodKlass>
5: 17416 808920 <symbolKlass>
6: 1000 559280
[Lorg.apache.derby.impl.store.raw.data.StoredRecordHeader;
The page cache is expected to contain ~4MB of byte arrays, but the
StoredRecordHeader objects consume even more memory, ~6.5MB.
> 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
>
>
> 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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