Raj Mathur wrote:
Hi,
Writing a web-based application using PostgreSQL as the back-end
database. The master create functions look something like this:
1. Accept ID from user.
2. Verify that ID doesn't exist in database. Start transaction.
Create blank record with ID as key.
3. Accept remaining data for record from user.
4. Enter data into newly-created blank record. End transaction.
Firstly,is it possible to have a transaction spanning multiple
instances of the CGI/mod_perl invocations?
Not easily. You are not always guaranteed the same httpd process when
connecting. HTTP is stateless.
Second, there are issues if the user session terminates for some
reason (e.g. user goes offline after the blank record has been
created, etc.) and I end up with a locked blank record in the
database. Would appreciate pointers to best practises in handling
this paradigm.
It is basically a poor design when using HTTP operations. You are
better off using server-side session data to store all the information
you will need for the complete database operation and then at your final
stage of data entry do the record addtion inside of a transaction (i.e.
one POST operation), if you want to rollback on error. This should
eliminate your concerns over lost locks and hanging transactions.
Unrelated, but I find at least 3 different interfaces to PostgreSQL
from Perl: DBI, Pg and PgSQL. I'm using Pg at the moment, since that
ships with PgSQL by default with Red Hat, but are there any reasons to
choose one over the other?
Regards,
-- Raju
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