Display BLOB from remote database

Question

Context: We are offloading documents (pdf) from our OLTP database to a dedicated 'output database.' These documents must be displayed from the application on our OLTP database using a database link. Various posts show that querying a BLOB from a remote database can best be implemented using a query on the remote table and an insert on a local (temporary) table. So far, so good. The idea is to display this BLOB using wpg_docload.download_file.
BUT:
When trying to display the pdf from this global temporary table an error occurs:
ORA-14453: attempt to use a LOB of a temporary table, whose data has already been purged
When trying to display from a normal table and issuing a rollback after wpg_docload.download_file results in another error:
ORA-22922: nonexistent LOB value
When trying to display from a normal table and not removing the record in any way, its works fine. Only I now have a garbage collection issue, because the remote date remain in my local (preferably temporary) table.
It seems to me that mod_plsql needs an active session to display my pdf.
Does anyone have an explanation for this behaviour and maybe a solution for my problem?
Environment:
local: 10.2.0.4.0
remote: 11.1.0.7.0
pdf size: ca. 150kB
code used:
PROCEDURE show_doc (p_nta_id IN NUMBER
,p_sessie IN NUMBER
IS
t_lob BLOB;
t_lob2 BLOB := empty_blob();
t_mime VARCHAR2(100);
BEGIN
-- copy BLOB into local global temp table
INSERT INTO mvs_tmp_notaprint_bestanden
npv_nta_id
, npv_npe_sessie
, mime_type
, bestand
) -- from remote table
SELECT npd.npv_nta_id
,npd.npv_npe_sessie
,npd.mime_type
,npd.bestand
FROM mvs_notaprint_bestanden@marc npd
WHERE npd.npv_nta_id ; = p_nta_id
AND npd.npv_npe_sessie = p_sessie
-- show BLOB from local global temp table
SELECT t.bestand
, t.mime_type
INTO t_lob
, t_mime
FROM mvs_tmp_notaprint_bestanden t
WHERE t.npv_nta_id ; = p_nta_id
AND t.npv_npe_sessie ; = p_sessie
t_lob2 := t_lob; -- buffer BLOB
owa_util.mime_header(t_mime , FALSE );
owa_util.http_header_close;
wpg_docload.download_file(t_lob2);
END show_doc;

Answer 1

Andrew,
thank you, the 'preserve rows' did the trick.
Every query from a browser (even in the same browser session) is a new Oracle session, so the copied records in the global temporary table are gone after the page is displayed.
Am I correct in assuming that each call from the browser results in a new Oracle session? I did a few tests and found for each call a different sessionid.
Sincerly,
Arne Suverein
Edited by: Arne Suverein on Aug 18, 2009 3:35 PM