This is why I said that using RowData when transferring columns with BLOB
contents is dangerous...

So much so that I am tempted to raise an exception if you try it...

Regards,
Jason Wharton
CPS - Mesa AZ
http://www.ibobjects.com

----- Original Message -----
From: <noreply@...>
Newsgroups: mers.interbase.build
To: <prenosil@...>; <noreply@...>;
<firebird-devel@...>
Sent: Tuesday, November 21, 2000 6:07 AM
Subject: [Firebird-devel] [Bug #123056] Blob-IDs are sometimes shared
between more rows


> Bug #123056, was updated on 2000-Nov-21 05:07
> Here is a current snapshot of the bug.
>
> Project: Firebird
> Category: Core Engine
> Status: Open
> Resolution: None
> Bug Group: Confirmed
> Priority: 5
> Summary: Blob-IDs are sometimes shared between more rows
>
> Details: In SP, when you copy record (from/to the same table) by
> INSERT INTO tab SELECT ... FROM tab WHERE ...;
> or by
> SELECT ... FROM ... INTO _local_variables_;
> INSERT INTO tab VALUES (_local_variables_);
>
> and the record contains BLOB, then _sometimes_
> newly created row will not contain its own copy
> of the BLOB, but instead it will use the same
> blob-id as the original record.
> (i.e. single blob is shared among more rows)
>
> This is really severe bug, because it will cause
> data lost - when you delete one of these rows,
> and then try to read the other one, you will get
> "BLOB not found" error !!!
>
> Interestingly, when you execute exactly the same
> command directly, not as part of SP, blob-ids will be o.k.
>
> Here is script to reproduce this bug:
> =====================================
> CREATE DATABASE 'C:\test.gdb' USER 'SYSDBA' PASSWORD 'masterkey';
>
> CREATE TABLE t (
> i INTEGER,
> b BLOB );
>
> SET TERM ^;
>
> CREATE PROCEDURE p (x INTEGER) AS
> BEGIN
> INSERT INTO t (i,b)
> SELECT i+100, b FROM t WHERE i=:x;
> END^
>
> SET TERM ;^
>
> COMMIT;
>
> /* insert some blob into our test table */
> INSERT INTO t (i,b)
> SELECT 1, rdb$trigger_blr
> FROM rdb$triggers
> WHERE rdb$trigger_name='RDB$TRIGGER_1';
>
> COMMIT;
>
>
> /* now make copy of that row ... */
> /* INSERT INTO t (i,b)
> SELECT i+100, b FROM t WHERE i=1; */
> INSERT INTO t (i,b)
> SELECT i+100, b FROM t WHERE i=1;
> INSERT INTO t (i,b)
> SELECT i+100, b FROM t WHERE i=101;
> INSERT INTO t (i,b)
> SELECT i+100, b FROM t WHERE i=101;
>
> SET BLOBDISPLAY OFF;
> /* ... and show result; */
> /* all blobs will have different blob-ids */
> SELECT * FROM t;
>
> ROLLBACK;
>
> /* now execute the same insert statements, but wrapped in SP */
> /* EXECUTE PROCEDURE p 1; */
> EXECUTE PROCEDURE p 1;
> EXECUTE PROCEDURE p 101;
> EXECUTE PROCEDURE p 101;
>
> /* here you will see that blob-id is shared ... */
> SELECT * FROM t;
>
>
> /* and here you can see what will happen when one row is deleted ... */
> SET BLOBDISPLAY ALL;
> DELETE FROM t WHERE i=101;
> COMMIT;
> SELECT * FROM t;
>
>
> /************
> One more test - uncomment first of "EXECUTE PROCEDURE p 1" commands
> and run this script again - you will see correct blob-ids,
> i.e. the wrong behaviour is not consistent.
> ************/
>
>
>
> For detailed info, follow this link:
> http://sourceforge.net/bugs/?func=detailbug&bug_id=123056&group_id=9028