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From Oystein.Grov...@Sun.COM (Øystein Grøvlen)
Subject Re: [jira] Created: (DERBY-510) DERBY-132 resolved ? Table not automatically compressed
Date Wed, 17 Aug 2005 13:26:57 GMT
>>>>> "MM" == Mike Matrigali <mikem_app@sbcglobal.net> writes:

    MM> Note that derby does automatically reclaim space from deletes
    MM> for subsequent inserts, but the granularity currently is at
    MM> a page level.  So deleting every 3rd or 5th row is the worst
    MM> case behavior.  The page level decision was a tradeoff as
    MM> reclaiming the space is time consuming so did not want to
    MM> schedule to work on a row by row basis.  Currently we schedule
    MM> the work when all the rows on a page are marked deleted.

It seems like you are mixing two things here:

  1. Reclaiming space for subsequent inserts in the same table, and

  2. Reclaiming space to the file system (which can be used for
     inserts into other tables).

I do not understand why reclaiming of space for 1. should be time
consuming.  You can have a list of pages that have lot of free space,
each time you delete a record so that the amount of free space is
above a certain threshold, the page is added to this list.

For 2., it does not seem to happen automatically even for empty pages?
I have today deleted all records of a table with a 440MB file.  The
size of the file has not changed.

-- 
Øystein


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