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Showing entries 1 to 28

Displaying posts with tag: speculations (reset)

Fun with Bugs #32 - some bugs I've reported in March
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Comparing to the previous month I was not really productive bug reporter in March 2014 (partially because I spent few days at a nice FLOSS UK conference where I tried to give a session on PERFORMANCE_SCHEMA). Just 12 reports, of them 5 documentation requests are already closed. There are some interesting reports among other 7 to write about though.

But let me start with good (or not entirely good) news about my older report, Bug #71858 (easy way to crash MySQL with single SELECT

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Fun with Bugs #31 - what's new in MySQL 5.6.17
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MySQL 5.6.17 will probably be announced loudly at or immediately before Percona Live MySQL Conference & Expo next week. But official release announcement via email was made on March 28, release notes and binaries to download are already available, so why not to check them carefully to find out what to expect from this 8th minor release of MySQL 5.6 GA...

First of all, it seems Oracle still does not hesitate to introduce new features and behavior in the process. Just check these major changes:
  • Starting with 5.6.17, MySQL now supports rebuilding regular and partitioned InnoDB tables using



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What's wrong with MySQL Manual
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I think that MySQL Manual is one of the reasons why MySQL became and still remains popular. I find a lot of useful information (at least references to share with customers, if not real insights) there even after 9+ years of working with MySQL every day and with all numerous articles and blog posts on most important topics available now. I still have MySQL manual page open at every browser instance on every laptop I use on a regular basis.

It's simply great, well indexed by Google and has meaningful human-readable URLs, so one can even guess them for the topics he need. I have http://dev.mysql.com/doc/refman/5.6/en/merge-storage-engine.html open right now and looking at it I clearly understand without any search that if I need a reference for SELECT syntax in

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Fun with Bugs #30 - quick review of my reports in February, 2014
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I've got only one comment to my previous post about deadlock, and it was more like a hint based on a different use case, not a real explanation. So far there is nobody who wants to get free beer... Maybe this is even good, as I do not go to the conference and BOF I've submitted will be supervised by my colleague Przemysław Malkowski. But you still have entire month till the conference to get a chance for a beer from him (we'll arrange this somehow).

In the meantime I'd like to review bug reports for MySQL server (few) and fine manual (many) that I've submitted in February, 2014. 22 in total, one

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Magic deadlock: what locks are really set by InnoDB?
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Megabytes of text had been written already on InnoDB locking and deadlocks. Still, even very simple cases of deadlocks while working with a table having only one row sometimes make people wonder what happened and why.

Today I want to check if this topic is explained well in the manual and existing blog posts and understood properly. So, it's an exercise for my dear readers and those who like to report bugs as much as I do.

Let's consider a very simple example. In session #1 with default transaction isolation level execute the following:
CREATE TABLE `tt` (
  `id` int(11) NOT NULL,
  `c1` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `c1` (`c1`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
insert into tt values(1,1); -- insert a row there
select * from tt; -- check that











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On responsible bugs reporting
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Let me start with questions related to responsible MySQL bugs reporting that I'd like to be discussed and then present a history behind them.

Assuming that you, my dear reader from MySQL Community, noted or found some simple sequence of SQL statements that, when executed by authenticated MySQL user explicitly having all the privileges needed to execute these statements, crashes some version of your favorite MySQL fork, please, answer the following questions:
  • Do you consider this kind of a bug a "security vulnerability"?
  • Should you share complete test case at any public site (MySQL bugs database, Facebook, your personal blog, any)?
  • Should you share just a description of possible "attack vector", as Oracle does when they publish security bug fixes?
  • Should you share just a stack trace or failed assertion information,



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    Fun with Bugs #29 - important bug fixes in MySQL 5.6.16
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    As you should already know, Oracle had released MySQL 5.6.16 officially on January 31, 2014. You can find all the details in official release notes. In this post I decided to concentrate on important fixes for bugs reported by community in 4 most important categories: InnoDB, replication, partitioning and optimizer.

    Let's start with Bug #70768, "Persistent optimizer statistics often causes LOCK_open stalls". It's well known that persistent statistics for InnoDB tables stored in two (again, InnoDB) tables in mysql database may cause various problems, not only bad plans based on outdated statistics there. One of these problems seems solved in 5.6.16, but note that the bug report itself

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    Fun with Bugs #28 - regression bugs in MySQL 5.6
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    2013 was a great year for MySQL Community. New MySQL 5.6 GA release with its increased throughput, scalability and new features as well as more interaction and cooperation with MySQL Community from Oracle side brought us a lot of new perspectives and good feelings over the year.

    Unfortunately new MySQL 5.6 GA release also reminded about old and well known problem with new MySQL versions. They all introduce new regression bugs. MySQL 5.6 had not become an exception.

    Note that according to good old tradition (that I hope will be followed in 2014) bugs that demonstrate a regression (make some feature that previously worked stop functioning as intended in a new release) are marked with "regression" tag at http://bugs.mysql.com.



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    Fun with Bugs #26 - MySQL bugs Oracle had not fixed for me (yet)
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    In the previous post in this series I've listed 15 MySQL bug reports, documentation and feature requests I've made in 2013 that got fixes or any other kind of solution. Now it's time to check what happened to the rest and try to think why.

    First of all, no MySQL bug reporter is perfect (if only Domas), so some bug reports may be false alarms ("Not a bug"), to hard to fix at any foreseeable future ("To be fixed later") or

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    Fun with Bugs #25 - MySQL bugs Oracle fixed for me this year
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    I've checked recently and noted that I've sent 50 reports about MySQL bugs, features I'd like to see and unclear/missing manual pages this year. It all started with famous Bug #68079 (reported on January 14, 2013), that got a lot of attention, valuable workaround from Oracle and caused a lot of work that is going to improve MySQL scalability substantially in the future.

    Oracle had also implemented this my (and not only mine!) feature request, Bug #69527, and in MySQL 5.7.3 PERFORMANCE_SCHEMA finally exposes metadata locks information. This is a great and long waited step forward in instrumentation.

    Besides that, 12 of my documentation requests were satisfied:





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    Teaser on my upcoming Percona Live London 2013 session
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    As you probably know already, I have a session on PERFORMANCE_SCHEMA at the conference, scheduled at 12 November 4:00pm - 4:50pm @ Orchard 1. Presentation is mostly ready, but I had not decided yet when to publish it. In the meantime, for those really interested, here is a teaser.

    Below I list one link for each slide (in order of presentation) having more than one of them mentioned or listed in my notes. Now try to guess what I am going to say there and why. Note that it's not a tutorial (my half a day tutorial on PERFORMANCE_SCHEMA was not accepted by the conference committee, and this is probably good decisions, as I am usually very good in explaining what's bad or what should never be done and much worse in "best practices"). So,

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    Recalculating InnoDB Persistent Statistics - a Story of the Bug Report
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    One of the first posts in this blog was about reporting MySQL bugs "properly", in a way that maximizes chances for it to be processed really soon. I had written the following there:
    "Ideally, you should provide a complete test case and/or instructions that any reader can use to reproduce your problem"
    Indeed, if one can just copy/paste something to mysql command line client or run some file attached to see the problem, chances are high for the bug to be processed really soon. We all like to get low hanging fruits from time to time, and Oracle engineers who work on bugs are not exceptions. But does this mean that bug without clear test case has no value and is going to be ignored?

    It should NOT be the case. Let's


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    Fun with Bugs #24 - PERFORMANCE_SCHEMA
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    It seems that one of my session proposals is accepted for Percona Live London 2013, so I have to prepare myself to speak about PERFORMANCE_SCHEMA new features and problems in MySQL 5.6. Bugs are going to be discussed, among other things. Let's check current active bugs (and some "Not a bug"s) related to PERFORMANCE_SCHEMA in this issue.

    I'd like to start with Bug #68514 that got some attention this week again, in despite of its "Not a bug" formal status. Detailed instrumentation comes with a cost, and to reduce high CPU cost (reported as Bug #67736 by Domas at 5.6 RC stage) it was decided to

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    It's all about bugs fixed: MySQL 5.6.14
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    Most of MySQL gurus and famous users are probably in San Francisco now, getting ready for fun at MySQL Connect. Part of that fun should come from the announcement of great new MySQL 5.6.14 release (that somewhat silently happened yesterday).

    I am sitting at home though and I've seen at best 3 sunny days in September. The rest of the time it rains, so hardly I can do anything more funny and useful than review of MySQL bug reports even during my weekend. Let me try to tell you what MySQL 5.6.14 is really about and what you should expect from it based on the list of bugs fixed. Please, do not blame me if my summary would be different from the upcoming keynotes at MySQL Connect. It rains here...


    I'll use good old approach of checking my older posts




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    Fun with Bugs #23 - more on Optimizer bugs in MySQL 5.6
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    When I've sent CV to MySQL AB back in 2004 (or early 2005) I had actually wanted to become a developer there. As a person who just started to use MySQL on a regular basis and, at the same time, had to explain dozens of engineers per month how optimizers works in Oracle and Informix RDBMSes, and optimize queries for them from time to time, I was naturally interested in adding missing (but well known to me) features to MySQL optimizer (from hash joins to stored outlines, histograms and tracing, all things I've noted as extremely useful for many real life cases)... So, I wanted to work on MySQL optimizer specifically, if something related to MySQL at all.

    It happened so that MySQL Support had somehow noted my CV before anybody else, so in few months and after some serious tests and long screening talks (the longest of them was with new, at the time,

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    MySQL Bugs Verification - Is It Really Simple?
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    While it was explained already by Sveta and others what does it really mean to "Verify" (or "Confirm", in Launchpad/Percona's terms) a bug in MySQL software, and why this step in a bug's life cycle is important, we still often read complains about too much time taken to verify the bug even with a clearly repeatable test case that can be just copy/pasted, like Bug #69985 or notably more serious Bug #69990. Moreover, I often make  [Read more...]
    Fun with Bugs #21 - recently verified bugs in MySQL 5.6.13
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    Notable contribution of MySQL Community to MySQL 5.6.13 was explicitly recognized recently. But users and contributors still continue their efforts, as well as Oracle engineers. Even though MySQL 5.6.13 has been generally available just for few days, we already have several new bug reports and updates to known bugs at http://bugs.mysql.com. Let me present a short list with some comments.

    • Bug #69915 is a great example of a "new thinking" inside Oracle. Todd Farmer does not only write about new ways to use PERFORMANCE_SCHEMA in MySQL 5.6 in his blog, but also reports


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    Fun with Bugs #20 - welcome MySQL 5.6.13!
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    MySQL 5.6.13 is released today! Installation is in progress right now, so I had not checked anything yet personally in reality, but we have release notes to study.

    I'll base my quick review on my older posts devoted to known bugs in MySQL 5.6.12 in three main areas: InnoDB, optimizer and replication. All quoted text below is taken from the release notes.

    Let's start with InnoDB. From my "top 10" list I only see the following bug fixed in 5.6.13:
    • Bug #69316. "Performance; InnoDB: A code regression introduced in MySQL 5.6 negatively





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    What is the problem with "To be fixed later" bug status?
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    Bug #69842 was actively discussed on Facebook recently. Mostly not it's technical content - people do agree that InnoDB probably needs separate doublewrite buffer(s) for every possible InnoDB page size. It's more about bugs processing approaches, so I have to say something about this.

    The story was simple enough. I've mentioned this bug in my previous post and yesterday my dear friend Sinisa added some comments and set status to "To be fixed later". This had made bug reporter (who co-incidentally is a "small data

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    Fun with Bugs #19 - waiting for MySQL 5.6.13 and some real fun?
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    I feel like MySQL 5.6.12 was released ages ago, while in reality it was on June 3, less than 2 months ago. No wonder I feel so, after writing several posts about bugs fixed and not fixed in it... Anyway, we still have to wait for MySQL 5.6.13 for a week or even two probably and in the meantime I decided to write new post for this series based on good old idea of making a digest of my recent bugs-related posts at Facebook. I know, it's boring and annoying (same as waiting for the release of 5.6.13).

    Let's start with Bug #69846 - "ICP does not work on UNIQUE indexes". Based on my quick tests presented there I'd say that ICP (

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    Fun with Bugs #18 - Feature Requests (Oldies but Goldies Part II)
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    In the previous "Fun with Bugs" posts I've mostly ignored feature requests. Users do file a lot of feature requests in MySQL bugs database, but until recently (when "Affects Me" button was introduced) there was no clear way to even try to influence the priority of the feature in development plans. There is still no way to see if the feature request has any priority. Surely, based on Oracle policies, nobody from Oracle will even try to give you a hint on when the "Verified" feature request is going to be implemented or what is its real internal priority...


    Does it mean that there is no sense to make feature requests (or, for Oracle engineers, to process them and keep status in sync with reality)? No, it does not, IMHO. This is still one of few ways for a community user or even a customer to influence the future of MySQL. Even if Oracle will not start


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    Fun with Bugs #16 - read the fine MySQL 5.6 manual...
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    MySQL 5.6 has many new features and some of them change usual DBA procedures and formerly well known facts/limitations. It's important to have all these properly documented now, when MySQL 5.6 is GA for 6 months already and is supposed to be widely used in production. So, I think it's time to check what documentation problems still remain.

    Here is the list of active bug reports in Server: Docs category for version 5.6, starting with recently reported:

    • Bug #69717 - "DML statements replicated via RBR are NOT logged in the general query log ". I had to report this while working on customer issue and trying to explain why there are no DML statements in slave's general query log. This feature was new in 5.1 and even somewhat documented at




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    Fun with Bugs #15 - Recent News and Hawthorne Effect Studies
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    Let me present a quick review of new and recently verified MySQL bug reports (mostly in 5.6.12, but not only). Surely I have to start with this request that many my colleagues had already mentioned in their blogs:

    Bug #69558 - Put *all* know bugs into the public bug tracking system at bugs.mysql.com. We may argue on how and when this should apply to "security" bugs, but automatic bi-directional replication (even if delayed) with Oracle internals bugs database is what I was also asking for since we were forced to use it. Click on "Affects Me" button there and let's hope that some day Oracle will publish list of bugs that affect most of community users and may even try to take this into account while making decisions.

    I have good news for everybody who was following MySQL 5.6



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    Fun with Bugs #14 - InnoDB in MySQL 5.6
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    InnoDB improvements in MySQL 5.6 are well known. One of the key reasons to upgrade to MySQL 5.6 for most users is to get the benefits of improved performance, scalability, new monitoring features and fulltext indexes support in InnoDB.

    Is there anything to double check before assuming that InnoDB in MySQL 5.6 is just better than any older version for any practical purposes? Let's review known public InnoDB-specific bug reports. Here is my "Top 10" list, as of MySQL 5.6.12, starting with most recent reports:

  • Bug #69424  - maybe I miss something (I am not the only one though), but I see no way to continue using raw devices (on Linux at least) to store InnoDB data. You had working raw device in 5.5.32, then you upgrade to 5.6.12 and just can not start MySQL any more.




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    Fun with Bugs #12 - MySQL Cluster 7.3 GA
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    I had always tried to avoid all kinds of clusters, from Oracle RAC to MySQL NDB Cluster and Percona XtraDB Cluster, as much as possible. But these days clusters become common and it seems new developments in this area can not be just ignored. So, I decided to devote this issue of "Fun with Bugs" to MySQL Cluster 7.3, that was released as GA this week and still is in the news.

    The release was mostly about adding foreign keys support (one of the features that some users were missing for years comparing to InnoDB and other cluster database solutions). At the same time, MySQL Cluster is now based on MySQL Server 5.6 code. I've decided to quickly check how community adopted 7.3 and what it means in terms of bug reports.

    If one would just search for active bugs in version "7.3" at the public bugs



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    Fun with Bugs #10 - recently reported bugs affecting MySQL 5.6.12
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    MySQL 5.6.12 is available to community for more than a week already, so people started to test and use it. And, no wonder, new bug reports started to appear. Let's concentrate on them in this issue.

    I'd like to start with a funny one.  Bug #69413 had scared some of my Facebook readers to death, as we see kernel mutex mentioned clearly in the release notes for 5.6.12. What, kernel mutex comes back again? No, it's just a result of null merge and, probably, copy/paste from the release notes for 5.5.32.

    It seems recent bug reports for 5.6.12 are mostly related to small details



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    Fun with Bugs #9 - MySQL 5.6.12, quick review
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    So, it seems we have MySQL 5.6.12 released officially. We have great Changes in MySQL 5.6.12 page already widely shared and people already blogging about a feature implemented by my dear friend Sinisa.

    Quick scroll over changes shows 130+ bugs fixed and it will surely take time to understand the impact of all these fixes. We have 2 months for this till next release, so eventually we'll find out what's good in MySQL 5.6.12 and should we immediately switch to it from all other older 5.x.y versions.

    But we have to start with something, and I'd like to start with bugs that I've mentioned in



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    Fun with Bugs #8 - what's wrong with Oracle's way of handling public MySQL bugs database
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    Many people seem unhappy with the way Oracle develops MySQL. I am not one of them. I think very few really important things are missing and in this post I'd like to concentrate on one of them: having internal and public bugs databases not in sync in too many cases.

    Let me quote myself to explain where problem starts:

    "Now the most important thing you should know about MySQL bugs processing the way it is done now in Oracle. When bug is "Verified" and(!) considered serious enough, it is copied to the Oracle internal bugs database and further processing, including status changes etc, is done there. All further comments to the public bug report are then copied to internal bug report automatically, but no comments or




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    Showing entries 1 to 28

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