[jira] Updated: (DERBY-3130) Reduce memory footprint of StoredRecordHeader

["Knut Anders Hatlen (JIRA)" <ji...@apache.org>]

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

Knut Anders Hatlen updated DERBY-3130:
--------------------------------------

    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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