The latest from the MySQL community

I had the opportunity to review a client’s production Drupal installation recently. This is a new site and traffic is just starting to pick up. Drupal is a popular LAMP stack open source CMS system using the MySQL Database.

Unfortunately I don’t always have the chance to focus on one product when consulting, sometimes the time can be minutes to a few hours. Some observations from looking at Drupal.

Disk footprint

Presently, volume and content is of a low volume, but expecting to ramp up. I do however find 90% of disk volume in one table called ‘watchdog’;

+--------------+--------------+--------------+-------------+--------+
| table_schema | total_mb     | data_mb      | index_mb    | tables |
+--------------+--------------+--------------+-------------+--------+
| xxxxx        | 812.95555878 | …

MySQL by default is vary lax with data validation. Silent conversions is a concept that is not a common practice in other databases. In MySQL, instead of throwing an error, a warning was thrown and many applications simply did not handle warnings. With the introduction of sql_mode=STRICT_ALL_TABLES (or TRADITIONAL), in MySQL 5, a better level of validation now exists.

My understanding was that Warnings are now thrown as Errors, therefore eliminating the need to do a SHOW WARNINGS to confirm any problems after every query (this is a performance overhead on a high volume system due to the round trip latency).

However I found an instance where MySQL in STRICT Mode still throws warnings, leading to the question, are there any other areas, and does the earlier statement “Warnings are now thrown as Errors” hold true.

Here is my seeding process to showing the problem.

mysql> create table i(i tinyint, unique key( …

I was doing some database sizing in MySQL 5.1.30 GA for memory tables. Generally I have used INFORMATION_SCHEMA.TABLES data_length,index_length as a reasonable guide.

However working with a MEMORY table, after deleting rows, the size did not decrease as expected. I deleted 10% of rows, and saw 0% reduction. This was confirmed by doing a subsequent ALTER where I saw the 10% reduction in memory size.

It requires more investigation, however I found these results unexpected and worthy of publishing.

mysql> select version();
+-----------+
| version() |
+-----------+
| 5.1.30    |
+-----------+

+-----------------+--------+------------+------------+----------------+-------------+-------------+------------+
| table_name      | engine | row_format | table_rows | avg_row_length | total_mb    | data_mb     | index_mb   |
+-----------------+--------+------------+------------+----------------+-------------+-------------+------------+
| …

The 2009 MySQL Conference has closed it’s submissions for papers. This year the motto is “Innovation Everywhere”.

Last weekend’s Open SQL Camp in Charlottesville, Virginia, we had the chance to talk about the movements in the MySQL ecosystem. I was impressed to get the details of the Percona MySQL Patches, but focus is still in 5.0. (Welcome to the Percona team Tom Basil) Our Delta is attempting now to integrate patches into various MySQL branches. There was an opening keynote by Brian Aker from Drizzle, and Drizzle team Jay Pipes and Stewart Smith on hand. It was also announced that MySQL 5.1.30 will be GA, available in early December.

But these …

We all know with MySQL you can use ORDER BY with a list of columns to return an ordered set, e.g. ORDER BY name, type, state;
I often use the syntax ORDER BY 1,2; which I’m surprised that some people do not know about.

However I needed to do some selective ordering of a type field, I didn’t want to for example have a lookup table just to join for ordering. While contemplating a means of achieving this, I asked a work colleague, who I figured may have just experienced this problem before. Lone behold I became the student as I discovered there is a third syntax with ORDER BY, using expressions.

mysql> create table test(name varchar(10) not null, type varchar(10) not null);
Query OK, 0 rows affected (0.06 sec)

mysql> insert into test(name,type) values
('Apples','Fruit'),
('Bananas','Fruit'),
('Carrots','Veg'),
('Onions','Veg'),
('Beer','Liquid'),
('Water','Liquid'),
('Crackers','Food');
Query OK, 7 rows affected (0.00 sec) …

The current US financial situation has claimed a victim in the Web 2.0 world — Uber. I’m not sure if this is the first significant name, but it will not be the last site running MySQL where investors will be quick to cut losses and move on.

So… A few years back I spent a LOT of time with Oracle ETL and BI products. I learned them inside and out, gave some user conference presentations, wrote a bunch of blogs, even Alpha tested a version of Oracle Warehouse Builder. Then I found “Open Source BI” and I’ve been heading breakneck into the world of MySQL, Pentaho, … A choice I do NOT regret - my consultancy is busier than ever and I love the Open Source BI play.

However - I miss seeing some of the old Oracle peeps at Open World. This year, I even registered for my free ACE pass to OOW but didn’t make it because I started two new projects this week. What I realized this year, was that I’m WAY out of touch with what’s going on in the land of Big Red O. The words and products for BI whiz past me - they don’t even look anything like they did just a couple of years back.

I hope everyone had a good time at OOW this year! I don’t see a path back to the land of …

Indexes are a great way to improve performed in a MySQL database, when used appropriately.
When used in-appropriately the impact can be a degradation of performance.

The following example from Movable Type shows how when reviewing the slow query log I found numerous occurrences of Inserts take 3 or more seconds, with no reported lock contention time for this insert.

# Query_time: 3  Lock_time: 0  Rows_sent: 0  Rows_examined: 0
SET insert_id=6281;
INSERT INTO mt_comment
(comment_author, comment_blog_id, comment_commenter_id, comment_created_by,
 comment_created_on, comment_email, comment_entry_id, comment_ip, comment_junk_log,
comment_junk_score, comment_junk_status, comment_last_moved_on, comment_modified_by,
comment_modified_on, comment_parent_id, comment_text, comment_url, comment_visible)
VALUES (...)

The impact here, is that SELECT statements to the mt_comment table …

Why you do not use GRANT ALL ON *.*?

I was with a client today, and after rebooting a MySQL 5.0.22 instance cleanly with /etc/init.d/mysqld service, I observed the following error, because you always check the log file after starting MySQL.

080923 16:16:24  InnoDB: Started; log sequence number 0 406173600
080923 16:16:24 [Note] /usr/libexec/mysqld: ready for connections.
Version: ‘5.0.22-log’  socket: ‘/var/lib/mysql/mysql.sock’  port: 3306  Source distribution
080923 16:16:24 [ERROR] /usr/libexec/mysqld: Table ‘./schema_name/table_name’ is marked as crashed and should be repaired
080923 16:16:24 [Warning] Checking table:   ‘./schema_name/table_name’

Now, I’d just added to the /etc/my.cnf a number of settings including:

myisam_recovery=FORCE,BACKUP

which explains the last line of the log file. When attempting to connect to the server via the mysql client I got …

It’s important that for any software application good standards exist. Standards ensure a number of key considerations. Standards are necessary to enforce and provide reproducible software and to provide a level of quality in a team environment, ease of readability and consistency.

If you were going to create a MySQL Naming Standard you have to make a number of key decisions. Generally there is no true right or wrong, however my goals tend towards readability and simplicity. In 2 decades of database design I’ve actually changed my preference between some of these points.

1. Pluralism

Option 1
All database objects are defined in the logical form, that being singular.

For example: box, customer, person, category, user, order, order_line product, post, post_category

Option 2

For database tables & views, objects are defined in plural. …