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Thread Invalid BLOB offset
Mon, Oct 5 2009 11:31 AMPermanent Link

Ries van der Velden
Hello,

We are getting the following error when inserting a record, with CopyOnAppend = True and when we are trying to access a BLOB field [fieldtype ftMemo] in
the new record with Field.AsString in the AfterInsert event. This only goes bad when the BLOB field is empty. Checking for Field.IsNull always returns False.

DBISAM Engine Error # 9998 Invalid BLOB offset into the table 'Keuring_partijen'

We are using DBIsam version 4.29.1 in a Client - Server environment.

Is this a known issue? And if yes, any idea when it will be fixed?

Regards Ries van der Velden
Mon, Oct 5 2009 1:55 PMPermanent Link

Tim Young [Elevate Software]

Elevate Software, Inc.

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Email timyoung@elevatesoft.com

Ries,

<< We are getting the following error when inserting a record, with
CopyOnAppend = True and when we are trying to access a BLOB field [fieldtype
ftMemo] in the new record with Field.AsString in the AfterInsert event. This
only goes bad when the BLOB field is empty. Checking for Field.IsNull always
returns False. >>

We have an open incident report for this already, and a fix will be
available in the next couple of days.

Thanks,

--
Tim Young
Elevate Software
www.elevatesoft.com

Tue, Oct 6 2009 5:43 AMPermanent Link

Ries van der Velden
>"Tim Young [Elevate Software]" wrote:
>
>We have an open incident report for this already, and a fix will be
>available in the next couple of days.

Hi Tim,

OK.

Some more info: We have build some work-arounds in the code to prevent the 'invalid BLOB offset' error with version 4.29.1, but now the databaseserver is
giving an out of memory error about every two hours. See the attached log file. The service is then consuming about 1.5 Gb of memory on the server. I
suspect this to be an effect of the BLOB errors, but posting it to let you know.

We are going back to version 4.27.4 untill the problem is solved.

Regards, Ries



Attachments: pkoDatabaseServices.log
Tue, Oct 6 2009 6:55 AMPermanent Link

"Eduardo [HPro]"
Ries

I think it is valid a warning about downgrade from 4.27 and shorter from
4.29:

The structure of BLB file is different and you can catch by a "corrupted
blob".

Eduardo

Tue, Oct 6 2009 12:33 PMPermanent Link

Tim Young [Elevate Software]

Elevate Software, Inc.

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Email timyoung@elevatesoft.com

Ries,

<<We are going back to version 4.27.4 untill the problem is solved. >>

As Eduardo indicated, you cannot do that without risking corruption of the
BLOBs.  The way that free BLOB blocks are recycled is completely different
in 4.28 or higher.

--
Tim Young
Elevate Software
www.elevatesoft.com

Wed, Oct 7 2009 3:20 AMPermanent Link

Ries van der Velden
>"Tim Young [Elevate Software]" wrote:

>As Eduardo indicated, you cannot do that without risking corruption of the
>BLOBs.  The way that free BLOB blocks are recycled is completely different
>in 4.28 or higher.

That's right. We are experiencing some corruption problems with the BLOB fields. But the thing is that i've made a backup prior to going back to verion
4.27.4 and the BLOB fields in the tables from this backup [only edited with 4.29.1] are also corrupted.

The alternative [?] was a cutomer with a crashing DB every two hours, in which we cannot guarantee any data at all.

One off the record question: What is normal memory consumption for a DBISAM DB Server with about 40 concurrent users?

Regards, Ries
Wed, Oct 7 2009 1:14 PMPermanent Link

Tim Young [Elevate Software]

Elevate Software, Inc.

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Email timyoung@elevatesoft.com

Ries,

<< That's right. We are experiencing some corruption problems with the BLOB
fields. But the thing is that i've made a backup prior to going back to
verion 4.27.4 and the BLOB fields in the tables from this backup [only
edited with 4.29.1] are also corrupted. >>

I don't understand what you're saying here at all.  Are you accessing the
tables that were updated with 4.29 using 4.27 or not ?  If not, then
repairing the tables with 4.29 should correct any issue with them, and make
them usable with 4.29.

<< The alternative [?] was a cutomer with a crashing DB every two hours, in
which we cannot guarantee any data at all. >>

The workaround would have been to disable CopyOnAppend for the time being
until I can get a fix out.  I just learned about this issue two days ago and
I'm working on a fix.

<< One off the record question: What is normal memory consumption for a
DBISAM DB Server with about 40 concurrent users? >>

It completely depends upon the application.  If you're experiencing
unbounded memory consumption, however, then there is something wrong.  My
first suggestion would be to repair the database tables and make sure that
you don't have any issues with the BLOBs, such as BLOB blocks that are
circularly-linked.

--
Tim Young
Elevate Software
www.elevatesoft.com

Thu, Oct 8 2009 4:36 PMPermanent Link

Tim Young [Elevate Software]

Elevate Software, Inc.

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Email timyoung@elevatesoft.com

Ries,

I cannot reproduce this here using 4.29 B1.  Would it be possible for you to
send me a sample project that reproduces this ?  The incident report that we
received was basically the exact same circumstances that you describe, but I
cannot seem to cause an error no matter what I do.

I'm holding up a B2 release until I can determine what is going on with
this.

--
Tim Young
Elevate Software
www.elevatesoft.com

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