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Displaying posts with tag: innodb (reset)
Percona Server for MySQL 5.7.21-20 Is Now Available

Percona announces the GA release of Percona Server for MySQL 5.7.21-20 on February 19, 2018. Download the latest version from the Percona web site or the Percona Software Repositories. You can also run Docker containers from the images in the Docker Hub repository.

Based on MySQL 5.7.21, including all the bug fixes in it, Percona Server for MySQL 5.7.21-20 is the current GA release in the Percona Server for MySQL 5.7 series. Percona …

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Troubleshooting MySQL Crashes Webinar: Q&A

In this blog, I will provide answers to the Q & A for the Troubleshooting MySQL Crashes webinar.

First, I want to thank everybody for attending our January 25, 2018, webinar. The recording and slides for the webinar are available here. Below is the list of your questions that I was unable to answer fully during the webinar.

Q: I have the 600 seconds “Long semaphore wait” assertion failure / crashing issue following DDL queries, sometimes on the master, sometimes just the slaves. Any hints for troubleshooting these? How can I understand what semaphore …

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Investigating a MySQL dead lock

I was involved in one of the development support for MySQL. Here is an interesting case

The application needs a Sequence generator as it was not present inbuilt with MySQL ( MariaDB will have it in 10.3 ) they have made sequence generator function with ‘select for update‘ statement. But it tends to cause more locking at high concurrency with their XtraDB Cluster deployment.

To get rid of this , the sequence generation were made as direct Update queries and sequence is fetched using Select @next.

UPDATE EO_PK_TABLE SET PK = (@next := PK …
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Fun with Bugs #61 - On MySQL Bug Reports I am Subscribed to, Part III

Since my previous post on this topic I've subscribed to 19 more MySQL bugs, so it's time for yet another review of these reports. I am trying to pick up important, funny or hard to process reports every day, and here is the list of the most interesting ones starting from the latest:

  • Bug #89607 - "MySQL crash in debug, PFS thread not handling singals." We have a patch contributed by Robert Golebiowski.
  • Bug #89583 - "no rpm build instructions from source git tree". As Simon Mudd put it:
    "... The sources are supposed to be in the git tree …
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This Week in Data with Colin Charles 27: Percona Live Tutorials Released and a Comprehensive Review of the FOSDEM MySQL DevRoom

Join Percona Chief Evangelist Colin Charles as he covers happenings, gives pointers and provides musings on the open source database community.

Percona Live Santa Clara 2018 update: tutorials have been announced. The committee rated over 300+ talks, and easily 70% of the schedule should go live next week as well. In practice, then, you should see about 50 talks announced next week. There’s been great competition: we only have 70 slots in total, so about 1 in 5 talks get picked — talk about a competitive ratio.

FOSDEM

FOSDEM was truly awesome last week. From a Percona standpoint, we had a lot of excellent booth traffic (being outside of the PostgreSQL room on Saturday, and not too far out from the MySQL room on Sunday). We gave away bottle openers — …

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Fsync Performance on Storage Devices

While preparing a post on the design of ZFS based servers for use with MySQL, I stumbled on the topic of fsync call performance. The fsync call is very expensive, but it is essential to databases as it allows for durability (the “D” of the ACID acronym).

Let’s first review the type of disk IO operations executed by InnoDB in MySQL. I’ll assume the default InnoDB variable values.

The first and most obvious type of IO are pages reads and writes from the tablespaces. The pages are most often read one at a time, as 16KB random read operations. Writes to the tablespaces are also typically 16KB random operations, but they are done in batches. After every batch, fsync is called on the tablespace file handle.

To avoid partially written pages in the tablespaces (a source of data corruption), InnoDB performs a doublewrite. During a doublewrite operation, a batch of dirty pages, from 1 to about 100 pages, is …

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Four Ways MySQL Executes GROUP BY

In this blog post, I’ll look into four ways MySQL executes GROUP BY. 

In my previous blog post, we learned that indexes or other means of finding data might not be the most expensive part of query execution. For example, MySQL GROUP BY could potentially be responsible for 90% or more of the query execution time. 

The main complexity when MySQL executes GROUP BY is computing aggregate functions in a GROUP BY statement. How this works is shown in the documentation for UDF Aggregate Functions. As we see, the requirement is that UDF functions get all values that constitute the single group one …

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On InnoDB's Online DDL

I am completing my preparations for the upcoming FOSDEM talk, and one of last things I wanted to do in frames of them is a quick review of known bugs and problems in current (as in MySQL 5.7 GA) implementation of so called "online" DDL for InnoDB tables.

In my previous post I already shared my view on another important InnoDB feature, persistent statistics. Unlike that, I do not really hate online DDL. I just try to avoid it if possible and use tools like pt-online-schema-change or gh-ost instead. Not because it is not documented properly (the …

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On InnoDB's Persistent Optimizer Statistics

As I put it in recent Facebook post, one of MySQL features that I truly hate is InnoDB's persistent statistics. I think I should clarify this statement. It's great to have a way to save statistics in between server restarts, to have better control on the way it is estimated (even on a per table basis), set it explicitly, check it with simple SELECT. These all are great additions since MySQL 5.6.2+ that I truly appreciate (even if I may not be happy with some implementation details). They helped to make plans for queries against InnoDB more predictable and allow (with some efforts applied) MySQL query optimizer to really work as "optimizer" instead of "randomizer" or "pessimizer" (as some people called it) for InnoDB tables.

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Fun with Bugs #60 - On Some Memory Leaks, Replication and Other Bugs Fixed in MySQL 5.7.21

Oracle had formally released MySQL 5.7.21 yesterday. I do not bother any more to study MySQL release notes carefully and completely, but during a quick review today I've noted several interesting items I'd like you to pay attention to.

I am historically interested in InnoDB implementation details, so I could not miss Bug #87619 - "InnoDB partition table will lock into the near record as a condition in the use ". This was a regression bug in 5.7+, probably caused by new implementation of partitioning in InnoDB.

Another interesting bug is Bug #86927 - "Renaming a partitioned table does not update mysql.innodb_table_stats.", by …

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