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"Invalid BLOB handle" problem

I am inquiring to find out more about this error and what is causing it. I'm using Delphi 2 with BDE v3.5 under SQL Server and Windows NT. Here is the line of code which generates the exception:

  ablobstream := TBlobStream.Create(ablobfield,bmRead);

The error message generated is:
 "Invalid BLOB handle in record buffer"

I've done a lot of searching on this particular error. Many people seem to get it, but no one has really replied to say what's causing it, or how to fix it.

Any help/information would be appreciated.
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csean
Asked:
csean
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1 Solution
 
arhCommented:
 This seems to be a bug in BDE. I encountered it when i tried
to display memo field contents in a grid connected to a query.
(server is Oracle).
I found that it occurs only if TQuery.RequestLive property is
set to false, and when you scroll several pages down and one page up. Setting RequestLive to true eliminates this error,
but also significally slows scrolling through data set.
  I tried to use direct  BDE API calls to read blob data, but it did not help (so the problem is not in TBlobStream).
  I don't know how this bug affect data sets which are tables (not queries) because I don't use TTable at all.
  Have anyone tried to submit this as a bug report to Borland?
(they say you can do it at www.borland.com)
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arhCommented:
I have found and (incomplete) answer on Borland web page.
It appears that for non-live cursors the number of accessed BLOBS is limited by BDE cache size, which can be adjusted in BDE 4.0.
Here is Borland answer:

Q: "Invalid BLOb handle" error: What is the cause and how do I fix this error?

A: If the error occurs on a non-live (dead, canned) query or a table with no indexes, then increasing the new BDE4.0 configuration parameter 'BLOBS TO CACHE' will fix the problem. This setting determines how many BLObs will be cached on the client. Applications that deal with fetching dead BLObs using dead table opens or queries can set a limit on the number of BLObs to cache depending on the resource available on the client. Setting a value 100 means the application can work with a maximum of 100 BLOb records cached. Fetching more than 100, then scrolling back 100 records results in an "Invalid BLOb handle in record buffer" error message.
NOTE: This parameter does not apply to live table opens.
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cseanAuthor Commented:
Thanks arh,

Your proposed answer fixed the problem we were having. Although
we did have to increase the value to 5000 because there was
nearly that many records in the result set.


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