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# Tag: sql_mode

## Those oversized, undersized variables defaults

MySQL Configuration sql_mode June 9, 2010June 9, 2010

Some mysqld parameters are far from having reasonable defaults. Most notable are the engine-specific values, and in particular the InnoDB parameters.

Some of these variables have different defaults as of MySQL 5.4. innodb_buffer_pool_size, for example, is 128M on 5.4. innodb_log_file_size, however, has changed back and forth, as far as I understand, and is down to 5M again. These settings are still the same on 5.5.

I wish to present some not-so-obvious parameters which, in my opinion, have poor defaults, for reasons I will explain.

- group_concat_max_len: This parameter limits the maximum text length of a GROUP_CONCAT concatenation result. It defaults to 1024. I think this is a very low value. I have been using GROUP_CONCAT more and more, recently, to solve otherwise difficult problems. And in most cases, 1024 was just too low, resulting in silent (Argh!) truncating of the result, thus returning incorrect results. It is interesting to learn that the maximum value for this parameter is limited by max_packet_size. I would suggest, then, that this parameter should be altogether removed, and have the max_packet_size limitation as the only limitation. Otherwise, I’d like it to have a very large default value, in the order of a few MB.
- wait_timeout: Here’s a parameter whose default value is over permissive. wait_timeout enjoys an 8 hour default. I usually go for 5-10 minutes. I don’t see a point in letting idle connections waste resources for 8 hours. Applications which hold up such connections should be aware that they’re doing something wrong, in the form of a forced disconnection. Connection pools work beautifully with low settings, and can themselves do keepalives, if they choose to.
- sql_mode: I’ve discussed this in length before. My opinion unchanged.
- open_files_limit: What with the fact connections, threads, table descriptors, table file descriptors (depending on how you use InnoDB), temporary file tables — all are files on unix-like systems, and considering this is an inexpensive payment, I think open_files_limit should default to a few thousands. Why risk the crash of “too many open files”?

Continue reading » “Those oversized, undersized variables defaults”

## But I DO want MySQL to say “ERROR”!

MySQL Configuration Data Types sql_mode Syntax March 12, 2010March 12, 2010

MySQL is known for its willingness to accept invalid queries, data values. It can silently commit your transaction, truncate your data.

- Using GROUP_CONCAT with a small group_concat_max_len setting? Your result will be silently truncated (make sure to check the warnings though).
- Calling CREATE TEMPORARY TABLE? You get silent commit.
- Issuing a ROLLBACK on non-transactional involved engines? Have a warning; no error.
- Using LOCK IN SHARE MODE on non transactional tables? Not a problem. Nothing reported.
- Adding a FOREIGN KEY on a MyISAM table? Good for you; no action actually taken.
- Inserting 300 to a TINYINT column in a relaxed sql_mode? Give me 255, I’ll silently drop the remaining 45. I owe you.

#### Warnings and errors

It would be nice to: Continue reading » “But I DO want MySQL to say “ERROR”!”

## MySQL security: data integrity issues

MySQL Configuration Security sql_mode January 21, 2009

MySQL’s security model is not as elaborate as other popular databases. It’s missing quite a lot.

I wish to point out what I think are some very disturbing security holes, which may affect the database integrity.

This post is not about Roles, Kerberos, IPs and such. It’s about simple MySQL features, which allow common, unprivileged users, to break data integrity by using unprotected session variables.

I will consider three such issues.

Continue reading » “MySQL security: data integrity issues”

## sql_mode: a suggestion

MySQL sql_mode January 11, 2009January 11, 2009

I thought this deserves more than a comment on my previous post on the subject, in which I expressed the opinion that sql_mode is undesired.

Back to reality: sql_mode is here right now. What else can be done?

#### Suggestion

Is there anything to do about sql_mode? I believe so: make it strict by default.

Continue reading » “sql_mode: a suggestion”

## Do we need sql_mode?

MySQL Configuration Installation sql_mode January 8, 2009January 9, 2009

sql_mode must be one of the most elusive issues in setting up a MySQL database. It is also responsible for difficulties in migration, upgrading and securing of databases.

MySQL usually has little issues with migrating database from one machine to another, one version to another, one OS to another, one architecture to another. If we’re not sure, we can always migrate using mysqldump’s logical dump, right?

Not entirely right. The elusive sql_mode (empty by default) may affect out backup+restore, may affect our application behavior, may affect our data integrity. Continue reading » “Do we need sql_mode?”