db-derby-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Andrew Lawrenson <andrew.lawren...@coppereye.com>
Subject Blobs & Delete speed
Date Mon, 20 Apr 2009 09:53:14 GMT

I've been experiencing a performance problem with deleting blobs in derby, and was wondering
if anyone could offer any advice.

This is primarily with under windows and solaris, although I've also tested with
the new release candidate (as it has many lob changes), but this makes no significant

The problem is that with a table containing many large blobs, deleting a single row can take
a long time (often over a minute).

I've reproduced this with a small test that creates a table, inserts a few rows with blobs
of differing sizes, then deletes them.

The table schema is simple, just:

create table blobtest( id integer generated BY DEFAULT as identity, b blob )

and I've then created 7 rows with the following blob sizes : 1024 bytes, 1Mb, 10Mb, 25Mb,
50Mb, 75Mb, 100Mb.
I've read the blobs back, to check they have been created properly and are the correct size.

They have then been deleted using the sql statement ( "delete from blobtest where id = X"

If I delete the rows in the order I created them, average timings to delete a single row are:

1024 bytes: 19.5 seconds
1Mb: 16 seconds
10Mb: 18 seconds
25Mb: 15 seconds
50Mb: 17 seconds
75Mb: 10 seconds
100Mb: 1.5 seconds

If I delete them in reverse order, the average timings to delete a single row are:
100Mb: 20 seconds
75Mb: 10 seconds
50Mb: 4 seconds
25Mb: 0.3 seconds
10Mb: 0.25 seconds
1Mb: 0.02 seconds
1024 bytes: 0.005 seconds

If I create seven small blobs, delete times are all instantaneous.
It thus appears that the delete time seems to be related to the overall size of the rows in
the table more than the size of the blob being removed.
I've run the tests a few times, and the results seem reproducible.

So, does anyone have any explanation for the performance, and any suggestions on how to work
around it or fix it?  It does make using large blobs quite problematic in a production environment...

Many thanks in advance,


View raw message