db-derby-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From T K <sanokist...@yahoo.com>
Subject Re: Horrible performance - how can I reclaim table space?
Date Thu, 24 Sep 2009 01:35:21 GMT
Ouch... I have! I will consider the upgrade

Thanks Bret.

From: Brett Wooldridge <brett.wooldridge@gmail.com>
To: Derby Discussion <derby-user@db.apache.org>
Sent: Wednesday, September 23, 2009 9:31:51 PM
Subject: Re: Horrible performance - how can I reclaim table space?

If you are on 10.3, you might consider, as a space reclamation issue for large objects
was resolved (http://issues.apache.org/jira/browse/DERBY-4050) between 10.3 and
 According to that defect, the upgraded version ( will still not reclaim space lost
prior to the update, so a full offline compression is required.


On Thu, Sep 24, 2009 at 10:03 AM, T K <sanokistoka@yahoo.com> wrote:

We have a horrific performance issue with a table of 13 rows, each one containing a very small
blob, because the table is presumably full of dead rows and we are table-scanning; here's
part of the explain plan:
>                        Source result set:
>                                Table Scan ResultSet for SOMETABLE at read committed isolation
level using instantaneous share row locking chosen by the
> optimizer
>                                        Number of columns fetched=4
>                                        Number of pages visited=8546
>                                        Number of rows
> qualified=13
>                                        Number of rows visited=85040
>                                        optimizer estimated cost:       787747.94
>So I assume I have over 85,000 dead rows in the table, and compressing it does not reclaim
the space. In fact, because we keep adding and deleting rows, the performance gets worse by
the hour, and according to the above plan, Derby has processed over 32MB of data just to match
4 of the 13 rows. For the time being, I want to optimize this table scan before I resort to
> indices and/or reusing rows. This is with Derby 10.3
>Any thoughts?

View raw message