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I was testing transaction support in innoDB tables, and just for the curriosity I tried to run the same transaction on MyIsam table, and surprisingly it worked. I am assuming that on myIsam table queries are executed one after another not in one atomic operation and I don't get any errors from START TRANSACTION and COMMIT and ROLLBACK operations. I am interested, is MyIsam engine just ignoring this operations or does it perform some actions?
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MyISAM stands for Indexed Sequential Access Method. It was the default storage engine for MySQL until December 2009. With the release of MySQL 5.5, MyISAM was replaced with InnoDB. MyISAM is based on an ISAM algorithm that displays information from large data sets fast.
However, the older MyISAM storage engine does not include support for foreign keys. This means that MyISAM tables that are reverse engineered will not automatically have the relationship lines drawn between tables, making the database harder to understand.
In terms of data queries (SELECT), InnoDB is the clear winner, but when it comes to database writes (INSERT and UPDATE), MyISAM is somewhat faster. However, the lower speed of InnoDB is more than compensated for by its transaction protocol.
Note that MySQL supports two different kinds of tables: transaction-safe tables (InnoDB and BDB) and non-transaction-safe tables (HEAP, ISAM, MERGE, and MyISAM).
MyISAM effectively works in auto-commit mode (as it's not a transactional engine), and it just ignores the commit/rollback.
Actually storage engine is a different layer in the MySQL architecture, separated from the SQL parser, the SQL layer communicates to the storage engine with lower-level API, and that's the reason there is a common SQL and engines, supporting different subset of featured. You can see very high-level overview of the architecture here
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MyIsam tabels were not built for this. Not even in the 5+ versions. It only was meant to store data. It gives you no guarantee for transactions or data recovery. You should use InnoDB for this and, if needed, use MyIsam for replication purposes (it's faster to retrieve data with MyIsam tables since there's no cross-table checks).
You may read this post from MySQL http://forums.mysql.com/read.php?21,68686,69229#msg-69229
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