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Showing entries 1 to 10 of 98 10 Older Entries

Displaying posts with tag: optimizer (reset)

Fun with Bugs #42 - Bugs Fixed in MySQL 5.7.12
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MySQL 5.7.12 was released more than 2 weeks ago. New features introduced there in a form of "rapid plugins" are widely discussed, but I am more interested in bugs reported by MySQL Community users that are fixed there. Unfortunately I do not see MySQL Community Release Notes by Morgan (like this) for quite a some time, so I have to continue describing key bug fixes and name people who reported and verified bugs in my "Fun with Bugs" series.

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Indexing JSON documents via Virtual Columns
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In a previous post I took the new JSON datatype and functions for a test drive, using sample data provided by SF OpenData. Today I will extend that example to include indexing.

Introducing Generated Columns

MySQL 5.7 introduces a new feature called generated columns.…

What to do with optimizer hints after an upgrade?
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At a recent optimizer webinar, I talked about MySQL introducing a new style for hints, and that MySQL 5.7 also added support for more hints, see Sergey Glukhov’s blog. A question I got at the end of the webinar was what to do with the hints in the application code after an upgrade?…

Fun with Bugs #41 - Bugs Fixed in MySQL 5.7.11
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I've just noted that Oracle had released new versions of MySQL on February 5, 2016 formally, so while these days I am mostly thinking about the ways to do support properly, remembering my colleagues and trying to understand some of RocksDB internals, it's time to postpone all these and write about bugs again. This time about some of the public bug reports from MySQL Community and Oracle engineers that were fixed by Oracle in MySQL 5.7.11.

As usual, I'll try to mention who had reported a bug and who verified it, as I think that names …

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MySQL Support People - Percona Support
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I planned to continue this series of posts with the one about MySQL Support engineers who joined us in Oracle while I was working there, but based on recent events in my life I'd prefer to postpone it and move directly to the team I worked for during last 3+ years, Percona Support Team.

Disclamer: In the list below I still try to pay attention to public contribution by each of engineers mentioned to MySQL Community, mostly in a form of bug reports. This is not the only way they contributed, but I have to stick to this format in current series of posts. I also base my comments mostly on my memory and quick search of public …

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Tricking the Optimizer, or How Checking Bug Reports Help to Solve Real Problems
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I've got several useful habits over the years of work in MySQL Support. One of them is to start working on every problem with search for known MySQL bugs related to the problem at hand. I'd like to share one recent case where this habit helped me to get a solution for customer almost instantly.

It was one of rare cases when customer opened a support request with a very clear question and even a test case. The problem was described very precisely, more or less as follows (with table and column names, and data changed for this blog post, surely).

Let's assume we have two tables created like these:





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Fun with Bugs #40 - Bugs fixed in MySQL 5.7.10
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MySQL 5.7.10, the first release after MySQL 5.7 GA announcement, appeared almost a week ago. It's interesting to check what bugs reported by MySQL Community were fixed in this version, hence this post (that had to wait during the weekdays busy with usual support work). As usual, I'll concentrate mostly on InnoDB, replication and optimizer-related bug fixes and highlight names of those who reported and verified each bug.

Let's start with InnoDB. The following bugs reported by MySQL Community users were fixed:




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MySQL 5.7: Improved Performance of Queries with Derived Tables
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In a recent blog post my colleague Roy presented his work for MySQL 5.7 that makes the query optimizer merge sub-queries in the  FROM clause (so-called derived tables) with the outer query.  I will in this blog post show an example of how this work improves the performance of a MySQL query.…

Derived Tables in MySQL 5.7
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In MySQL 5.7, we have enhanced the optimizer so that derived tables and views are handled more consistently.

Just to recap: A derived table is a subquery that can take the place of a table in the FROM clause of an SQL statement.…

WITH RECURSIVE and MySQL
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If you have been using certain DBMSs, or reading recent versions of the SQL standard, you are probably aware of the so-called "WITH clause" of SQL.
Some call it Subquery Factoring. Others call it Common Table Expression.
In its simplest form, this feature is a kind of "boosted derived table".

Assume that a table T1 has three columns:


CREATE TABLE T1(
YEAR INT, # 2000, 2001, 2002 ... …






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Showing entries 1 to 10 of 98 10 Older Entries

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