Concurrency Problem

[THUNDER44]

How do you prevent 2 users from updating the same table within a database in php? I am using mysql database. Are there any codes to tackle this problem? I prefer isolating one user while the data is entered by another user in the database or Locking.

[rachel2004]

If you mean preventing deadlocking, the default MySQL engine (myisam) prevents that with table-level locking. But if what you mean instead, is to completey keep one person from doing any updates, use the GRANT statement to limit/revoke his privileges to any table in your db, assuming you yourself have the privileges to do that. Hope that helped.

[THUNDER44]

Sorry! What I have written is not clear.
The solution to my problem will be to completely prevent one user from not only to update but also to prevent from reading the information from a table in a database when another user (who accessed it first) is reading the same table in a database. What codes do you use to tackle this problem?

[wilku]

In MySQL you can use LOCK TABLES. I never used it myself, so I can't provide any example.

[THUNDER44]

Thank You guys!

[Drakla]

Lock tables might not be the solution here - because of mysql's limit of locking the WHOLE table when doing this, it stops access to any document in the table reading or writing if you open it with write privileges.

And is this like, somebody sits down, starts editing the document, then saves it back, sort of thing?

If so you could add a table flagging documents as open for editing by user X and deny others access to it, making sure you remove the entry when it's written back, or add a timestamp and have a timeout period where they're not classed as locked any more, in case somebody doesn't check out.

[THUNDER44]

Thank You Drakla. It solved the problem