CODEWITHSUNDEEP
pythonmysqltransactions
chris
chris

Reputation: 2020

Is it possible to check for db updates before performing db.rollback() within a worker transaction?

I'm using a queue to queue transactions for a MySQL database in python. I'm using autocommit=False so that I can rollback a transaction if not all of the data queries are executed properly.

I'm wondering whether it's possible to check whether a worker has performed an action on the database before performing db.rollback()? Or can you perform db.rollback even if a worker hasn't done anything to the database without any errors occurring?

Thanks!

Upvotes: 0

Views: 38

Answers (2)

EagleRainbow
EagleRainbow

Reputation: 951

If you issue a 

START TRANSACTION;

(which brings the connection into the same as autocommit = false), sending the command

ROLLBACK WORK;

(see also https://dev.mysql.com/doc/refman/5.5/en/commit.html ) returns with 

0 row(s) affected

So, this means, you may rollback an empty transaction safely (tested on MySQL 5.1.49-3).

Alternatively, you always may store in a worker a local/static variable, which is initialized with false. If at least a single update command has been issued by the worker, you set this variable to true.

If you have to decide later on whether to ROLLBACK or not, you just look at the variable: if it true, you know that you have sent a least one update command through the DB channel.

Upvotes: 0

Darwin von Corax
Darwin von Corax

Reputation: 5246

If I've understood the question correctly, it is not an error to rollback a transaction where nothing else has happened, although it is an error to attempt to rollback when no transaction exists. To tell which is the case you can test the MySQLConnection.in_transaction property.

Upvotes: 2

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