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Posted by e_matthes on 05/08/07 02:48
Hello everyone,
I have read many threads about concurrency issues, and I think I
understand some of the pieces, but not the whole picture.
I believe I am like many people using php: developing a personal
website on a windows machine, that will be hosted on a shared linux
server. Financial reality makes it impossible to think of a dedicated
server, and I'm not ready to jump into developing on a linux box.
I am looking at how to efficiently code some database operations,
while using a MyISAM mySQL database. The options seem to be:
1. Use flock() in the code to lock a semaphore file. This sounded
fine, until I read that different systems respond to flock()
differently, and we get into making temporary directories and checking
if they exist. This seems difficult to develop on a local machine,
then play around on the shared server environment.
2. Use LOCK TABLES in mysql. This would be fine, but results in
locking tables more often and more restrictively than they need to be
locked.
3. Use a lockStatus table. I make a row that's called
"registerNewUser" and set it to "locked"; do my work; then set
"registerNewUser" back to "unlocked". This is fine, but if the user
clicks out or the steps are not completed, "registerNewUser" remains
set to "locked".
What I am leaning towards is a LOCK TABLES approach that tries to
mimic the semaphore file approach.
A- I create an empty (semaphore) table called registerNewUser.
B- I get a write lock on this table, and a read lock on all tables
needed for the subsequent work.
C- I release the locks.
Any other operation that would conflict with registering a new user
would also get a lock on the semaphore table registerNewUser. What I
think this achieves is that any other user can read from the tables
that are being written to (which is not usually a problem - if it is,
that user gets a read lock on the appropriate semaphore table). Also,
if the connection is lost, the lock is released.
Can anyone shoot holes in this thinking? Am I right in thinking this
reasonably imitates the semaphore file approach?
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