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From "Mikael Sundberg" <Mikael.Sundb...@artificial-solutions.com>
Subject RE: how to get data out from Clob?
Date Tue, 25 Nov 2008 13:59:28 GMT
Thanks for the info 
Does the same problem exist for Blob?
Will update my testservers and try it. 

-----Original Message-----
From: Kristian.Waagan@Sun.COM [mailto:Kristian.Waagan@Sun.COM] 
Sent: den 25 november 2008 14:01
To: Derby Discussion
Subject: Re: how to get data out from Clob?

Mikael Sundberg wrote:
> Hi
> Im using derby 10.4.2 and the clientdriver.
> I changed from 
>                 BufferedReader r = new BufferedReader(new
> InputStreamReader(res.getAsciiStream("data")));
>                 for (String line = r.readLine(); line != null; line =
> r.readLine())
>                 {
>                     w.println(line);
>                 }
>
> To
> 	String data = res.getString("data");
>
> In a recent update to our application since the getString seemed to be
> twice as fast then. Not entirely sure what versions of derby I tested
on
> then.
> So bacisly I should change back now?

On the client driver, it doesn't matter (with respect to the bug I'm 
talking about). I'm afraid you're stuck with the performance problem 
until you upgrade to a newer version.

> We don't want to use any unstable
> version on production so guess I will have to solve it some other way.

> Il atleast try out the latest version on my testservers to see if that
> realy is the problem.
>   

I would consider using the newest bits from the 10.4 branch. The changes

after the latest release are bug fixes, not new features.
You can download test binaries from here 
http://dbtg.thresher.com/derby/bits/
Note that these are bits used for the nightly testing and should *not* 
be used in production without verification and testing.

Note that the performance problem in this case is severe; the larger the

Clob the worse the impact (we're talking hours instead of 
seconds/minutes). I would strongly suggest you test with a newer, though

unreleased, version.


-- 
Kristian

>  
> -----Original Message-----
> From: Kristian.Waagan@Sun.COM [mailto:Kristian.Waagan@Sun.COM] 
> Sent: den 25 november 2008 13:32
> To: Derby Discussion
> Subject: Re: how to get data out from Clob?
>
> Mikael Sundberg write:
>   
>> We are having some trouble with retrieving data from big Clob fields.

>> The data is about 40-50MB and it takes forever to retrieve it.  
>>
>> Tried a lot of different methods, getString, getClob, getAsciiStream.

>> They all take forever (hours).
>>
>> When checking whats running in derby we find
>>
>> CALL SYSIBM.CLOBGETSUBSTRING(?, ?, ?)
>>
>> A lot of times.
>>
>> How should I retrieve large CLob fields fastest?
>>
>>  
>>
>>     
>
>
> Hello Mikael,
>
> You are being hit by a serious performance bug (a lot more prominent 
> since Derby 10.3).
> I understand you are using the client driver, but which version of
Derby
>
> are you using?
>
> I believe the issue you are experiencing has been fixed in trunk and
in 
> the 10.4 branch, but a release hasn't been made after the fix was 
> committed. If you don't want to build Derby yourself, *test binaries* 
> are available if you want to test with a newer version. It should be 
> sufficient to update the server side only (i.e. derbynet.jar and 
> derby.jar). If you try it out, please remember to take a backup of
your 
> database! If you need to upgrade you database to trunk, you also need
to
>
> enable pre-release upgrades.
>
> Unfortunately, there is no way to properly work around the problem in 
> older releases. You can adjust the buffer/block size used to fetch
data 
> in the client application, but this will only help a little bit and
will
>
> probably not be sufficient.
> The optimal buffer size is dependent on the Clob content (due to the 
> UTF-8 encoding used). If your Clobs contain ASCII data, you should set

> your buffer size to 32672 (note that this is smaller than 32KB). If
you 
> are using the embedded driver, make sure you access the Clob using one

> of the streaming methods (getSubString has been fixed by now).
> There will be several changes regarding Clob performance in the next 
> feature release.
>
> We're also in the progress of adding performance regression tests for 
> LOBs, as this is a problem we should have detected a long time ago!
> If you are still seeing the problem with the newest version, I'm very 
> interested in getting more details from you.
>
>
> regards,
>   


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