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From "Mike Matrigali (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5356) Tracking for Derby space reclamation issues
Date Wed, 14 Sep 2011 17:25:11 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5356?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13104687#comment-13104687

Mike Matrigali commented on DERBY-5356:

Some comments on expected behavior and debugging space loss issues:
1) Derby will never automatically give space back to operating system while deleting rows
from a table.  It has various methods for reusing this space eventually for future inserts
to the table.  The only way to get derby to give back unused
space in a table and its indexes is to manually call one of the 2 compress routines:  SYSCS_UTIL.SYSCS_COMPRESS_TABLE

2) SYSCS_UTIL.SYSCS_COMPRESS_TABLE is the recommended compress option.  It is guaranteed to
reclaim the maximum amount of space possible and return it to the OS.  It will lock the entire
table for the duration of the operation,
other threads will automatically wait while the compress procedes.

3) SYSCS_INPLACE_COMPRESS_TABLE can do some of its work concurrently with other updating processes.
 But it will request a table level lock in the phase that returns space to the OS.  As with
other defragmenters it does not guarantee
to return all space to the OS.  It also does no work on indexes as currently Derby only can
shrink an index with a table level lock.

> Tracking  for Derby space reclamation issues 
> ---------------------------------------------
>                 Key: DERBY-5356
>                 URL: https://issues.apache.org/jira/browse/DERBY-5356
>             Project: Derby
>          Issue Type: Task
>          Components: Store
>            Reporter: Kathey Marsden
> This issue is being used to track various Derby space reclamation issues. 
> Users have reported the need to do periodic compress due to these issues, so opening
this issue for centralized tracking of the problem and also to help users identify which issue
they are hitting and possible work arounds.

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