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10.29.2007 at 02:36AM PDT, ID: 22923907
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9.8

Gotcha when updating LOBs via OCCI

Asked by davidhq in Oracle Database

Tags: , ,

hi!

I discovered that when I try to update a blob with a new blob that is shorter in size, the data from the first blob is left behind.

Example might help:
- there is a 100k blob in a column
- I update it with another 200k blob -> everything is ok
- I update that with a new 50k blob -> now the size stays at 200k with first 50k from the new blob and the rest from the previous one

I really didn't expect that behaviour.. am I lacking a broader understanding how OCCI really works?

Anyway.. I managed to figure a "dirty workaround".. It seems to work, but I don't like it and besides I'm not sure if there is no "orphaned data" left around in the database.


Current solution (suppose LOB_COL contains a 200k binary lob):

- get a Blob from the database ("SELECT LOB_COL FROM TABLE WHERE ID=1 FOR UPDATE"; .....
Blob blob = rset1->getBlob (2);)

- Set blob object to empty (blob.setEmpty();) and UPDATE it back ("UPDATE TABLE SET LOB_COL=:val1 WHERE ID=1;"

- After that run EMPTY_BLOB() function.. if not, I get LOB Locator errors.. so "UPDATE TABLE SET LOB_COL=EMPTY_BLOB() WHERE ID=1"

- Get Blob object from the DB again (same as the first step)

- Populate the blob (from a 50k file) (blob.getStream() and stream->writeBuffer())

- Update it again


Please help me understand why this happened and suggest the right way to make it work.. or at least tell me that my solution is good enough after all.. (or it even has to be done that way). Thank you very much!

DavidStart Free Trial
 
Keywords: Gotcha when updating LOBs via OCCI
Title
1 Oracle LOB Issue??
2 Writing Reading LOBS
3 LOB Error !!
4 Converting LongRaw to LOB ?
5 Unsupported LOB problem
6 table with lob field and storing lob at fil…
 
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[+][-]10.29.2007 at 08:30AM PDT, ID: 20170290

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About this solution

Zone: Oracle Database
Tags: examples, lobs, occi
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Solution Provided By: schwertner
Participating Experts: 1
Solution Grade: A
 
 
 
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