Showing entries 1 to 3
Displaying posts with tag: repeatable read (reset)
Looking deeper into InnoDB’s problem with many row versions

A few days ago I wrote about MySQL performance implications of InnoDB isolation modes and I touched briefly upon the bizarre performance regression I found with InnoDB handling a large amount of versions for a single row. Today I wanted to look a bit deeper into the problem, which I also filed as a bug.

First I validated in which conditions the problem happens. It seems to happen only in REPEATABLE-READ isolation mode and only in case there is some hot rows which get many row versions during a benchmark run. For example the problem does NOT happen if I run sysbench with “uniform” distribution.

In terms of concurrent selects it also seems to require some very special conditions – you need to have the connection to let some …

[Read more]
MySQL performance implications of InnoDB isolation modes

Over the past few months I’ve written a couple of posts about dangerous debt of InnoDB Transactional History and about the fact MVCC can be the cause of severe MySQL performance issues. In this post I will cover a related topic – InnoDB Transaction Isolation Modes, their relationship with MVCC (multi-version concurrency control) and how they impact MySQL performance.

The MySQL Manual provides a decent description of transaction isolation modes supported by MySQL – I will not repeat it here but rather focus on performance implications.

SERIALIZABLE – This is the strongest …

[Read more]
Runaway history list

On one of the clusters at Spil we noticed a sudden increase in the length of the history list and a steep increase in the ibdata file in the MySQL directory.
I did post a bit about this topic earlier regarding MySQL 5.5 but this cluster is still running 5.1 and unfortunately 5.1 does not have the same configurable options to influence the purging of the undo log…

Now I did find a couple of great resources that explain the purge lag problem into detail: Pythian, DimitriK and …

[Read more]
Showing entries 1 to 3