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From Oystein Grovlen - Sun Norway <Oystein.Grov...@Sun.COM>
Subject Re: [jira] Commented: (DERBY-2107) Move page latching out of the lock manager
Date Fri, 15 Dec 2006 10:09:19 GMT
Mike Matrigali (JIRA) wrote:
> The case I am trying to work out in my mind is the space reclamation thread.  It gets
latches on pages and 
> loops through rows requesting zero duration locks to see if it can purge a row from a
page.  In the first case
> the row we are requesting a lock on will never be purged as it is not possible for the
reclaim space thread to
> get a latch on a the page and purge the row we are waiting for a lock on (the lock request
for an update lock
> will fail because of our wait).  In the second case It can sneak in between the release
of the latch and queue
> of the waiting lock.

Looking at the code for purging deleted records, it does not seem to me 
that this operation uses the mechanism discussed here.  As far as I can 
tell, latches are not released until the entire page has been processed. 
  That is, the latch will not be released if the thread needs to wait 
for a lock.

-- 
Øystein

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