Q:

When it is time for a table to change from MyISAM to InnoDb?

This question is like a continuation of my previous question:
Am I right that InnoDb is better for frequent concurrent updates and inserts than MyISAM?
But this time I have concrete questions.
We know that MyISAM is faster than InnoDb when we don't have many concurrent updates (inserts). When we have many concurrent updates MyISAM table gets locked and all other clients should wait.
1) But when it is time to change from MyISAM to InnoDb? 1 update every second? 10 updates every second? 100 updates every seconds?
2) For a concrete example, will it be better to change to InnoDb one of the tables on my website where I usually have a few updates per minute (from different sessions), but sometimes it can be ~2-3 updates per second?

A:

I think your questions were pretty much answered in the previous question you referred to.
1) When you create the table.  InnoDB provides more advantages than merely row-level locking. Better speed when you have multiple sql clients doing updates, less risk of data loss/corruption, referential integrity etc...  With only a few transactions per second (TPS) you're not likely to tell the difference in the performance, but InnoDB is more reliable and scales better.
2) With only 2-3 TPS you will not see any significant difference between InnoDB and MyISAM.  Even on semi-ancient hardware.
FYI, a modern disk drive should be able to handle at least ~200 update transactions per second.
I recommend that you read up on InnoDB, MVCC and ACID.

