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10 Newer Entries Showing entries 61 to 70 of 124 10 Older Entries

Displaying posts with tag: bugs (reset)

How to use PERFORMANCE_SCHEMA to check InnoDB mutex waits
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SummaryTo set up InnoDB mutex waits monitoring via PERFORMANCE_SCHEMA in general with MySQL 5.6.9 you should do at least the following:

  1. Start MySQL server with all mutex related instruments enabled at startup (performance_schema=ON by default on recent 5.6.x), like this:

    mysqld_safe --performance_schema_instrument='wait/synch/mutex/innodb/%=on' &
  2. Connect to server and set up proper consumers explicitly, like this:

    UPDATE performance_schema.setup_consumers SET enabled = 'YES' WHERE name like 'events_waits%';
  3. Run your problematic load. …





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MySQL, the strange case of a timestamp field
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I discovered a feature (or bug) of MySQL timestamp fields. Maybe is documented in some place what I not read yet:

When I add a new timestamp field to a table, MySQL magically adds some features to new timestamp field like a “trigger” and a default value to CURRENT_TIMESTAMP.

There is test-case script:

-- CREATING TABLE AND INSERT SOME DUMMY DATA
mysql> CREATE TABLE t(
    -> id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
    -> val VARCHAR(50)
    -> );
Query OK, 0 ROWS affected (0.15 sec)
 
mysql> INSERT INTO t (val) VALUES ("foo") ,("var");
Query OK, 2 ROWS affected (0.08 sec)
Records: 2  Duplicates: 0 …
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My take on privatized MySQL security bugs
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A couple weeks ago I submitted Bug #67315: Crashing server by stored function referencing user defined variable in query. If you press that link, you can't see the bug (though I can as I submitted it).

This is due to Oracle's policy for security-related bugs. Tomas Ulin, Vice President MySQL Development at Oracle , was kind enough to discuss Oracle's policy with me, and these are the key points as I understand them:

Oracle's basic approach is to protect its customers. By publicizing security-bugs, Oracle's customers are vulnerable to black hatters attacks. …

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SkySQL and MariaDB Working Together to Keep MySQL an Open Ecosystem
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I pledged, in my first post last month, that SkySQL will do its part to promote the best of MySQL and its community. Given the recent discovery that Oracle is no longer publishing test cases for bug fixes, and the dialogue surrounding it, it feels like the right time to share my thoughts on what this means to the open source collective, and what we can do – and are doing – about it.

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MySQL 5.6 replication gotchas (and bugs)
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There has been a lot of talk about MySQL 5.6 replication improvements. With few exceptions, what I have seen was either marketing messages or hearsay. This means that few people have really tried out the new features to see whether they meet the users needs.

As usual, I did try the new version in my environment. I like to form my own opinion based on experiments, and so I have been trying out these features since they have appeared in early milestones.

What follows is a list of (potentially) surprising results that you may get when using MySQL 5.6.
All the examples are made using MySQL 5.6.6.

Gotcha #1 : too …


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Security fixes in MySQL & critical patch updates
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This is the third time MySQL has made an entry into the Oracle Critical Patch Update Advisory service. The first time, we at Team MariaDB came up with an analysis: Oracle’s 27 MySQL security fixes and MariaDB.

Security is important to a DBA. Having vague explanations does no one any good. Even Oracle ACE Director …

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The hidden mistake
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There are mistakes that drive you crazy when you try to understand what went wrong.

One of the most annoying and hard to catch was this, apparently harmless line:

tungsten-sandbox -m 5.5.24 --topology all-masters -n 2 -p 7300 -l 12300 -r 10300 –t $HOME/mm -d tsb-mm

The person reporting the error told me that the installation directory (indicated by "-t") was not taken into account.

I usually debug by examples, so I copied the line, and pasted it into one of my servers. Sure enough, the application did not take trat option into account. The installation kept happening in the default directory.

I knew …


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pt-diskstats 2.1 may return bad results
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Do you rely on pt-diskstats from Percona Toolkit instead of the standard iostat a lot? There appears to be a nasty bug in pt-diskstats 2.1, which makes it produce bad results.

I noticed some of the numbers I was getting weren’t right, so I tried running iostat and two different releases of pt-diskstat side by side. Here’s what I got:

I can understand the slight differences between the lines in iostat and pt-diskstats 2.0 as they probably weren’t reading /proc/diskstats contents in the same moments, so the values they were seeing could be a bit different. …

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MySQL must improve error messages
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I just finished a database modification, a new foreign key creation  shouldn’t be take more than 5 mins, but I spent 2 hours because MySQL still have some useless error messages.

There is a way to create a new foreign key:

-- Create two tables foo and bar
CREATE TABLE foo (
        id INTEGER NOT NULL PRIMARY KEY,
        bar_id INT NOT NULL    -- foreign key
);
CREATE TABLE bar (
        id INTEGER NOT NULL PRIMARY KEY
);
-- Try to create a foreign key on `foo`
ALTER TABLE foo
        ADD FOREIGN KEY(bar_id) REFERENCES bar(SOME_FIELD) ;

The last sentence returns a generic error message:

Error Code: 1005. Can't …

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How to submit a good database bug report
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When an open source project becomes popular, bug reports start flocking in. This is both good and bad news for the project developers. The good news is that someone is using the product, and they are finding ways of breaking it that we didn't think of. The bad news is that most of the times the reporters assume that the developers have super human powers, and that they will find what's wrong by the simple mentioning that a given feature is not working as expected. Unfortunately, it doesn't work that way. An effective bug report should have enough information that the ones in charge will be able to reproduce it and examine in lab conditions to find …

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10 Newer Entries Showing entries 61 to 70 of 124 10 Older Entries

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