![]() Different behaviorĪn obvious fact of the new Purge mechanism is that its behavior is quite different from the previous one, i.e. Previously, the purge thread was directly controlled by the main thread in InnoDB, causing serious side effects (more info here). The main change was moving out the purge thread and allowing it to run it isolated so that it doesn’t impact other processes. The move was done in Innodb 1.1 (present in 5.1 and 5.5).īut that is not all: The new version of purge has a mechanism that allows it to be more or less aggressive in relation to the increase or decrease of the History List length. This option is enabled in the 5.6 release and is taking the innodb_purge_threads as the “up to value” it can use to increase the number of threads for purging. History list is tightly bound to the undo log representing the number of Header Pages related to undo log segments, segments that are related to finalize transactions, commit, or roll back. That’s it: History list represents the number of not-yet-flushed segments in the undo log. MySQL uses (from Innodb 1.1 MySQL 5.5) 1 to 128 Rollback segments, each able to support 1023 transactions. Each transaction is assigned to one of the rollback segments and remains tied to that rollback segment for the duration of the transaction. This enhancement improves both scalability (higher number of concurrent transactions) and performance (less contention when different transactions access the rollback segments). ![]() This is because in 5.5 we have an intermediate situation, where the purge is not fully rewritten as in 5.6, but also not bound to the main thread. ![]() So again, why the article? Because I think there are some traps here and there, and I feel the need to write about them. The worse behavior is with MySQL 5.5. – 5.6. One of the things I was looking for was how the new Purge thread mechanism works and what were its implications. I have to say that it seems to work better than the previous versions, and the Dimitry blog (see reference) seems to confirm that. I began reading the code and performing tests. I started to compare versions, like 5.1 – 5.5. Then, I was reading a lot about the improvements we will have in MySQL 5.6 and about some already present in 5.5. Most of them are well covered by people that certainly know more than me, so I read and read, but after a while became curious. I have not found a link yet to provide reference to this.First of all, because I had fun digging in the code. His presentation will also cover Oracle’s investment in MySQL technology and community, as well as the role that open source in general is playing within heterogeneous customer environments around the world. He’ll discuss the current and future state of MySQL, now part of the Oracle family of products. ![]() Sebastopol, CA, February 24, 2010-Wonder about the future of MySQL? Curious about what Oracle plans for the open source database software? Expect answers when Edward Screven, Oracle’s chief corporate architect and leader of the MySQL business, speaks at the O’Reilly MySQL Conference & Expo, scheduled for April 12-15, at the Santa Clara Convention Center and the Hyatt Regency Santa Clara.Įdward Screven reports to CEO Larry Ellison, and he drives technology and architecture decisions across all Oracle products to ensure that product directions are consistent with Oracle’s overall strategy. Oracle Executive Will Speak at O’Reilly MySQL Conference & ExpoĮdward Screven to Answer Questions re: Future of MySQL For those of you on the O’Reilly MySQL conference list you will no doubt see this email, but for readers here is the important bits. ![]()
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