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Editorial Team
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Asked: 2026-06-05T05:20:55+00:00

I am working on a complex database application written with PHP and Mysqli. For

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I am working on a complex database application written with PHP and Mysqli. For large database operations I´m using daemons (also PHP) working in the background. During these operations which may take several minutes I want to prevent the users from accesing the data being affected and show them a message instead.

I thought about creating a Mysql table and insert a row each time a specific daemon operation takes place. Then I would be always able to check if a certain operation takes place while trying to access the data.

However, of course it is important that the records do not stay in the database, if the daemon process gets terminated by any reason (kill from console, losing database connection, pulling the plug, etc.) I do not think that Mysql transactions / rollbacks are able do this, because a commit is necessary in order to make the changes public and the records will remain in the database if terminated.

Is there a way to ensure that the records get deleted if the process gets terminated?

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  1. Editorial Team

    This is an interesting problem, I actually implemented it for a University course a few years ago.

    The trick I used is to play with the transaction isolation. If your daemons create the record indicating they are in progress, but do not commit it, then you are correct in saying that the other clients will not see that record. But, if you set the isolation level for that client to READ UNCOMMITTED, you will see the record saying it’s in progress – since READ UNCOMMITTED will show you the changes from other clients which are not yet committed. (The daemon would be left with the default isolation level).

    You should set the client’s isolation level to read uncommitted for that daemon check only, not for it’s other work as it could be very dangerous.

    If the daemon crashes, the transaction gets aborted and the record goes. If it’s successful, it can either mark it done in the db or delete the record etc, and then it commits.
    This is really nice, since if the daemon fails for any reason all the changes it made are reversed and it can be retried.

    If you need more explanation or code I may be able to find my assignment somewhere 🙂

    Transaction isolation levels reference

    Note that this all requires InnoDB or any good transactional DB.

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