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Hi,
I�d like to know if anybody has experimeted with following scenario:
I`m experimenting with a web application that runs on Tomcat 4.0.2 and it uses MySQL database. A servlet runs on a background that uses Jakarta Turbine to give database connections from the pool for each user.
In the "worst" scenario I can have multiple users on the JSP pages and each one has a connection to the database ( from the pool ), and each user can read and write the same data.
It`s really hard to find any info if these kind of scenarious are really thread safe. Most importantly are read/write operations on the same data atomic ( multiple threads / users using the same data ).
And if the database scenario would be thread / transaction safe, how does the Tomcat ( JSP -pages ) survive in the described scenario?
Any experience or knowledge?
Regards,
eki

Answer 1

Yes, I've encountered the same issue and as mentioned before - transactions are there exactly for that. BUT --
My scenario was that I needed to read a row from a table and than update it according to what I've just read. Meaning:
tx.begin()
select
update
tx.commit()
I've achieved that using TRANSACTION_SERIALIZABLE isolation level and I also HAD to specify the following table hint in the select statement: WITH (UPDLOCK). The later is needed in order to prevent any reads while in the transaction (reading or updating).
The only think I could not do is lock only the selected row and not the entire table (MS SQL 2000).
If anyone knows how to achieve that it'll make me a happy man...
Alon