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Displaying posts with tag: mutex (reset)

InnoDB scalability issues due to tables without primary keys
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Each day there is probably work done to improve performance of the InnoDB storage engine and remove bottlenecks and scalability issues. Hence there was another one I wanted to highlight:

Scalability issues due to tables without primary keys

This scalability issue is caused by the usage of tables without primary keys. This issue typically shows itself as contention on the InnoDB dict_sys mutex. Now the dict_sys mutex controls access to the data dictionary. This mutex is used at various places. I will only mention a few of them:

  • During operations such as opening and closing table handles, or
  • When accessing I_S tables, or
  • During undo of a freshly inserted row, or
  • During other data dictionary modification operations such as CREATE TABLE, or
  • Within the “Persistent Stats” subsystem,
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Why I am So Excited About the MySQL Performance Schema
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The improved Performance Schema in MySQL 5.6 provides a new way of investigating issues in the database. Many issues that previously required tools such as strace, dtrace, etc. can now be investigated directly from inside MySQL in a platform independent way using standard SQL statements.

The Performance Schema is enabled by default starting from the latest milestone release, 5.6.6. You have instruments which are the things you can measure, and consumers which are those that use the measurements. Not all instruments and consumers are enabled out of the box, however once the plugin is enabled, individual instruments and consumers can be switched on and off dynamically.

As an example take the case mentioned in What’s the innodb main

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MySQL 5.5: InnoDB Performance Improvements on Windows
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At MySQL, we know our users want Performance, Scalability, Reliability, and Availability, regardless of the platform the choose to deploy. We have always had excellent benchmarks on Linux, and with MySQL 5.5, we are also working hard on improving performance on Windows.

The original patch of improving Windows performance was developed by MySQL senior developer Vladislav Vaintroub; benchmarks by QA engineer Jonathan Miller. We integrated the patch into MySQL 5.5 release.

The following two charts show the comparison of MySQL 5.5 vs. MySQL 5.1 (plugin) vs. MySQL 5.1 (builtin) using sysbench:

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A growing trend: InnoDB mutex contention
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I’ve been noticing an undeniable trend in my consulting engagements in the last year or so, and when I vocalized this today, heads nodded all around me. Everyone sees a growth in the number of cases where otherwise well-optimized systems are artificially limited by InnoDB contention problems.

A year ago, I simply wasn’t seeing the need for analysis of GDB backtraces en masse. These days, I’m writing custom tools to gather and analyze backtraces. A year ago, I simply looked at the SEMAPHORE section of SHOW INNODB STATUS. These days I’m writing custom tools to aggregate and reformat that data so I can interpret it more easily. And I’m actually seeing cases of this type of problem multiple times every week. I remember the first time I ran into a server that was literally optimized to the limit, but struggling under the load. It

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Software is Hard Sometimes …
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Some months ago, Google released a patch for InnoDB that boosts performance on multi-core servers. We decided to incorporate the change into the InnoDB Plugin to make everybody happy: users of InnoDB don’t have to apply the patch, and Google no longer has to maintain the patch for new versions of InnoDB. And it makes us at Innobase happy because it improves our product (as you can in this post about InnoDB Plugin release 1.0.3).

However, there are always technical and business issues to address. Given the low-level changes in the patch, was it technically sound? Was the patch stable and as rock solid as is the rest of InnoDB? Although it was written for the built-in InnoDB in MySQL 5.0.37, we needed to

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Showing entries 1 to 5

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