Planet MySQL Planet MySQL: Meta Deutsch Español Français Italiano 日本語 Русский Português 中文
Showing entries 1 to 10 of 104 10 Older Entries

Displaying posts with tag: Geek (reset)

pt-online-schema change and row based replication
+0 Vote Up -0Vote Down

The way online schema changes have historically worked with statement based replication is to create an empty table on a slave, setup triggers to capture changes to a log table, copy the old table to the new table, apply the changes from the log table and atomic rename. This process breaks when using statement based replication because triggers don’t fire on events replicated to the slave. Triggers will fire on the master and the row events for any modified tables just replicate to the slave. This makes traditional online schema change break with statement based replication.

The workaround I’ve seen a few times at the …

  [Read more...]
Select into outfile and load data infile are not complementary by default
+1 Vote Up -0Vote Down

Configuring the character set for MySQL is confusing. It is so confusing that there are roughly 25 different places to configure a character set. Don’t believe me? Add them up. The real number may be closer to 30. I realize a lot of this is due to the age of MySQL and the extent of it’s character set support. MySQL does support character set configuration in many different places which is usually a good thing.

I often complain about defaults that make no sense like lock_wait_timeout=1 year. In this case there is a default that makes absolutely no sense to me. The manual says that select into outfile is …

  [Read more...]
How to get from MySQL SQL to C
+1 Vote Up -1Vote Down

Occasionally it is useful to know what a MySQL command is doing internally. Just looking into the MySQL source directory can be overwhelming. Knowing the basics of the handler interface and the sql parser can be a great start for reading the source code to understand what MySQL does under the hood. Here I will cover a little bit about how the SQL syntax is defined.

Everything starts with lex.h and sql_yacc.yy in the sql/ dir. lex.h contains all the functions and symbols used to make up the SQL syntax. The sql_yacc.yy file describes the relationships between these symbols and the C functions responsible for executing them. I’m not sure why some …

  [Read more...]
Percona Live Conference Notes
+3 Vote Up -0Vote Down

This is the required post about things I observed during this years MySQL conference.

Things that are awesome:

  • The tables in sessions. I think these were here last year. They are still awesome this year.
  • The new style power plugs. They solved the problem of people tripping over daisy chained power strips and the strips being accidentally turned off.
  • Massive quantities of coffee and real cream.

Things that can be improved:

  • Lunch tickets. I overheard the same conversation a dozen times about people not being able to find their lunch tickets or not really knowing about them. …
  [Read more...]
My new favorite example of why it isn’t a good idea to use reserved words as column names.
+4 Vote Up -1Vote Down

Some show commands support a where clause. The column name that can be used in the expression for the where clause depends on the result of the show command. For example in show tables the column is Tables_in_foo where foo is the database name.

MariaDB [test]> show tables where Tables_in_test = ‘t';
| Tables_in_test |
| t |
1 row in set (0.00 sec)

This is a problem with the show databases command because databases aren’t really *in* anything. Database is a reserved word so this …

  [Read more...]
Shutting down with mysqld, mysqladmin, SIGTERM, or SIGKILL.
+0 Vote Up -0Vote Down

How do you shutdown mysqld? I tend to use SIGTERM. People where I work tend to use mysqladmin shutdown. When things get bad I use SIGKILL. These three methods will end up with a dead mysqld but the one you choose depends on the situation and can even result in lost data. On Linux the difference between SIGTERM and SIGKILL is significant and often times misunderstood.

Before processes start to die it is important to understand the relationship between mysqld_safe and mysqld. mysqld_safe is the watchdog script for mysqld. It is responsible for starting mysqld and keeping an eye on it. It does this by waiting for mysqld to exit …

  [Read more...]
Percona Live MySQL Conference
+2 Vote Up -0Vote Down

These are things I like that I consider differences from last years conference. There are plenty of other things I like that don’t need to be listed here.

  • The overall tone and feel of the conference was much less marking and much more technical
  • Refreshingly honest keynotes. There was a lot of coming clean about the history of MySQL and the conference.
  • Percona is very technical but it is also a business. They are very good about bringing out the technical and not being pushy about the business.
  • No ice cream social. A thousand people shaking sticky hands with each other is never a good idea.
  [Read more...]
MySQL 5.0 can deadlock when flush logs, show processlist, and a slave connection happen at the same time
+0 Vote Up -0Vote Down

[ Note: I haven't fully investigated this problem but the post has been hanging around in my queue for months. Rather than have it rot there I am publishing what I know in hopes that it helps someone else. ]

There are a lot of different kinds of locks in MySQL. Some of these locks are exposed to users such as intention locks, table locks, and row locks. There are other locks that aren’t exposed as well. These are mutexes that MySQL uses internally to protect resources from being modified by more than one thread at a time. These locks are numerous and complicated. When these …

  [Read more...]
Is group_concat_max_len in bytes or characters?
+1 Vote Up -0Vote Down

The manual says bytes but sometimes it is measured in characters. It seems like group_concat_max_len is in bytes when being passed through a temporary table and in characters otherwise. This works fine when using latin1 but when converting to utf8 mysql must reserve 3 bytes per character when setting types in a temporary table. This is yet another reason to dislike group_concat..

mysql> create table group_concat_bug (str1 varchar(255), str2 varchar(255), str3 varchar(255)) charset=utf8 engine=innodb;
Query OK, 0 rows affected (0.02 sec)

mysql> show create table group_concat_bug;

  [Read more...]
The #mysql drinking game
+1 Vote Up -1Vote Down

These are the rules of the Freenode #mysql drinking game.

  1. Any non op posts a pastebin link either either the query and no error or the error and no query drink
  2. Any non op posts a query with, “why doesn’t this work?” without any explanation about the results they want or what they’re getting drink
  3. Domas trolls the channel with a legit issue drink
  4. When a postgres guy answers a question about sqlite in #mysql 3 drinks
  5. Someone answers a question with, “kill yourself” drink
  6. Someone asks a phpmyadmin question
  7. Someone asks a workbench question
  8. Someone can’t …
  [Read more...]
Showing entries 1 to 10 of 104 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.