Planet MySQL Planet MySQL: Meta Deutsch Español Français Italiano 日本語 Русский Português 中文
Showing entries 1 to 10 of 95 10 Older Entries

Displaying posts with tag: optimizer (reset)

Fun with Bugs #41 - Bugs Fixed in MySQL 5.7.11
+0 Vote Up -0Vote Down

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 …

  [Read more...]
MySQL Support People - Percona Support
+1 Vote Up -0Vote Down

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 …

  [Read more...]
Tricking the Optimizer, or How Checking Bug Reports Help to Solve Real Problems
+0 Vote Up -0Vote Down

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:





  [Read more...]
Fun with Bugs #40 - Bugs fixed in MySQL 5.7.10
+0 Vote Up -0Vote Down

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:




  [Read more...]
MySQL 5.7: Improved Performance of Queries with Derived Tables
Employee_Team +1 Vote Up -0Vote Down

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
Employee_Team +1 Vote Up -0Vote Down

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
Employee +3 Vote Up -1Vote Down

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 ... …






  [Read more...]
Fun with Bugs #38 - Regression Bugs in MySQL 5.6
+0 Vote Up -0Vote Down

I often have to reply to questions related to upgrade from, say, MySQL 5.5.x to latest MySQL (or Percona) Server 5.6.x (5.6.27 for MySQL and 5.6.26 for Percona at the moment). One of them is sometimes about "any known bugs" that may affect a user after upgrade.

One may assume that now, 2 years and 8 months after the first GA release of MySQL 5.6.10, there should be very few bugs (we call them regression bugs) of a kind that is interesting for the user planning upgrade from 5.5.x. I checked yesterday and found out it's not the case actually. It took me half an hour to end up with the list of more than 20 regression bugs that are …

  [Read more...]
Fun with Bugs #37 - Bugs fixed in MySQL 5.6.27
+1 Vote Up -0Vote Down

MySQL 5.6.27 was released on September 30 formally. Source code is also available on GitHub, and I have it compiled (some users are less lucky) and running for a couple of days already. In this post I'll comment on some bugs reported by MySQL Community that are fixed there.

I'd like to start with a couple of bugs where patches were also contributed. First of all, the fix suggested by Stewart …

  [Read more...]
on ORDER BY optimization
+1 Vote Up -0Vote Down

Generally in MySQL we send queries massaged to a point where optimizer doesn’t have to think about anything. In our major user database environment 99.9% of queries don’t have alternative query plans available (either because of forced indexes or just straightforward Primary Key read). We have various other systems and from time to time we have to do SQL work there and chase optimizer errors.

There’re multiple places where optimizer can make a choice in very basic queries, for example:

  • Which index returns less rows
  • Which index can be used for ORDER BY

A query that I was looking asked a very basic question, on a job …

  [Read more...]
Showing entries 1 to 10 of 95 10 Older Entries

Planet MySQL © 1995, 2016, Oracle Corporation and/or its affiliates   Legal Policies | Your Privacy Rights | Terms of Use

Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent the opinion of Oracle or any other party.