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The basics of the InnoDB undo logging and history system
InnoDB implements multi-version concurrency control (MVCC), meaning that different users will see different versions of the data they are interacting with (sometimes called snapshots, which is a bit of...
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A little fun with InnoDB multi-versioning
Consider the following commands, executed in the MySQL CLI on a new connection with no special preparation (and pay special attention to the execution time): mysql> show create table t \G...
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InnoDB with reduced page sizes wastes up to 6% of disk space
In InnoDB bugs found during research on InnoDB data storage I mentioned MySQL Bug #67963 which was then titled “InnoDB wastes 62 out of every 16384 pages”. I said: InnoDB needs to occasionally allocate...
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Thanks, Oracle for fixing MySQL Bug 69477
Just under a year ago, on June 14, 2013, I reported MySQL Bug 69477 (and MariaDB Bug MDEV-4662) titled “InnoDB: Use of large externally-stored fields makes crash recovery lose data”. The gist of this...
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Stupid and dangerous: SET GLOBAL sql_log_bin
It’s been almost 4.5 years since, during some code refactoring, it was decided (or accidentally changed?) that sql_log_bin should become a GLOBAL variable as well as a SESSION one. Almost 2 years ago,...
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Visualizing the impact of ordered vs. random index insertion in InnoDB
[This post refers to innodb_ruby version 0.9.11 as of October 2, 2014.] Many DBAs know that building indexes in “random” order (or really any order that greatly differs from ordered by key) can be much...
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Thanks, Oracle, for fixing the stupid and dangerous SET GLOBAL sql_log_bin!
As of MySQL 5.5.41, released on November 28 (last week), Oracle has fixed MySQL Bug 67433, which I filed on October 31, 2012 and wrote about 4 months ago in Stupid and dangerous: SET GLOBAL...
View ArticleReconsidering access paths for index ordering… a dangerous optimization… and...
MySQL has had an interesting optimization for years now1, which has popped up from time to time: in certain circumstances, it may choose to use an index that is index-wise less efficient, but provides...
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