Home |  MySQL Buzz |  FAQ |  Feeds |  Submit your blog feed |  Feedback |  Archive |  Aggregate feed RSS 2.0 English Deutsch Español Français Italiano 日本語 Русский Português 中文
Showing entries 1 to 7

Displaying posts with tag: new feature (reset)

Gluh on InnoDB extended secondary keys
Employee +1 Vote Up -0Vote Down
Sergey Glukhov (Gluh) recently wrote an interesting blog about InnoDB secondary key improvements in MySQL 5.6. His blog isn't aggregated to planet.mysql.com but certainly deserves some attention. 
Here it is: InnoDB, extended secondary keys.
Index merge annoyances fixed in MySQL 5.6
Employee +6 Vote Up -0Vote Down
While the index merge access types certainly are useful for a number of queries, there has been some frustration expressed both from customers and the community about how it...
  • is not used when it should have been
  • is used when ref access is obviously better
  • merges suboptimal indexes
  • is too restricted in which conditions can be used
  • I could come up with numerous examples of related bugs and feature requests dating back more than six years. To list a few: 17673, 30151, 23322,
      [Read more...]
    On queries with many values in the IN clause
    Employee +4 Vote Up -0Vote Down
    A few customers with rather extreme needs have contacted us about a performance issue with the range optimizer. Our solution to the problem is to introduce a new variable in MySQL 5.6, eq_range_index_dive_limit, which can be used to control whether or not the range optimizer will a) do index dives, or b) use index statistics when estimating the number of rows in the ranges of the query. The former method gives a far more accurate estimate while the latter costs a lot less to compute.

    This is what the help text has to tell about the variable:

    The optimizer will use existing index statistics instead of doing index dives for equality ranges if the number of equality ranges for the index is larger than or equal to [the value of variable]. If set to 0, index dives are always used.
    "Equality range" means predicates using operators



      [Read more...]
    Index Condition Pushdown to the rescue!
    Employee +2 Vote Up -0Vote Down
    A while ago, I explained how range access in a multiple-part index works and why MySQL can't utilize key parts beyond the first occurrence of some often used comparison operators. Luckily, there is a great improvement underway in MySQL 5.6 that will remedy much of this limitation. Meet Index Condition Pushdown.

    How does ICP work?

    Index Condition Pushdown is a new way for MySQL to evaluate conditions. Instead of evaluating conditions on rows read from a table, ICP makes it possible to evaluate conditions in the index and thereby avoid looking at the table if the condition is false.

    Let's assume that we have a multiple-part index covering columns (keypart_1, ..., keypart_n). Further assume that we have a condition with a





      [Read more...]
    Optimizer tracing: how to configure it
    Employee +1 Vote Up -0Vote Down
    In this blog post, my colleague Jørgen Løland described a new feature of MySQL 5.6: Optimizer Tracing. I recommend reading his article, as it presents this new feature in a simple, easy-to-read manner.

    The Optimizer Tracing feature can help understanding what the Optimizer is doing; it is available since milestone 5.6.3, announced October 3rd at Oracle Open World (here is the changelog). It's good to see it mature now; I remember that Sergey Petrunia did the first prototype back in March 2009!

    Today  I will be giving some must-have tips related to handling big traces.

    First thing to know, a trace lives in main memory (internally it is allocated on





      [Read more...]
    Optimizer tracing: Query Execution Plan descriptions beyond EXPLAIN
    Employee +6 Vote Up -0Vote Down
    Understanding why MySQL chooses a particular join order or why table scan is chosen instead of range scan is often very hard even for experienced MySQL users. Two almost identical queries, differing only in constant values, may produce completely different plans. That's why we're introducing a great new feature in 5.6: Optimizer Tracing. The target users of this feature are developers and MySQL users experienced enough to understand the ins and outs of EXPLAIN.

    What Optimizer Tracing is
    You may already have guessed this, but optimizer tracing is a printout  of important decisions the MySQL optimizer has done during the process of making the Query Execution Plan.

    The trace is presented in JSON format which is easy to read both for humans and




      [Read more...]
    Oracle’s Secret New Feature: Educated Guesses
    +0 Vote Up -0Vote Down

    Larry Ellison is announcing a major new feature this Wednesday at Open World. For the first time in a while, his keynote is dedicated to the “database” as opposed to the usual high level ERP/Apps/Fusion. Even the title of his keynote is catchy — “Extreme Performance”.

    Oracle has been keeping the new feature a secret. Even the 11gR2 beta program had very few participants to prevent information leaking out. It’s, “Something’s coming, but I am not telling what.”

    Okay, it worked on me, I’m excited about it. Let’s think what it could be. What

      [Read more...]
    Showing entries 1 to 7

    Planet MySQL © 1995, 2014, 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.