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Displaying posts with tag: Professional (reset)

Part 2 – Simple lessons in improving scalability
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Given the popular response from my first lesson in improving scalability where I detailed simple ways to eliminate unnecessary SQL, let me share another common bottleneck with MySQL scalability that can be instantly overcome.

Analyzing the writes that occur on a system can expose obvious potential bottlenecks. The MySQL Binary Log is a wealth of information that can be mined. Simple DML Counts per table can be achieved by a single line command.

Let’s look at the following example output of a production system:

mysqlbinlog /path/to/mysql-bin.000999 |  \
   grep -i -e "^update" -e "^insert" -e "^delete" -e "^replace" -e "^alter"  | \
   cut -c1-100 | tr
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Optimizing UPDATE and DELETE statements
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While most people look at performance optimizations for SELECT statements, UPDATE and DELETE statements are often overlooked. These can benefit from the principles of analyzing the Query Execution Plan (QEP). You can only run an EXPLAIN on a SELECT statement, however it’s possible to rewrite an UPDATE or DELETE statement to perform like a SELECT statement.

To optimize an UPDATE, look at the WHERE clause. If you are using the PRIMARY KEY, no further analysis is necessary. If you are not, it is of benefit to rewrite your UPDATE statement as a SELECT statement and obtain a QEP as previously detailed to ensure optimal indexes are used. For example:

UPDATE t
SET	c1 = ‘x’, c2 = ‘y’, c3 = 100
WHERE c1 = ‘x’
AND	d = CURDATE()

You can rewrite this UPDATE statement as a SELECT statement for using EXPLAIN:

EXPLAIN SELECT
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Simple lessons in improving scalability
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It can be very easy to improve scalability with a MySQL server by a few simple rules. Here is one of them.

“The most efficient way to improve an SQL statement is to eliminate it”

There are numerous ways to eliminate SQL statements, however before I give a classic example that I’ve observed again with a client, let me explain the basic premise of why this improves scalability?

The MySQL kernel can only physically process a certain number of SQL statements for a given time period (e.g. per second). Regardless of the type of machine you have, there is a physical limit. If you eliminate SQL statements that are unwarranted and unnecessary, you automatically enable more important SQL statements to run. There are numerous other downstream affects, however this is the simple math. To run more SQL, reduce the number of

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MySQL 5.5.9
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You blink and there is a new version. I have not seen an Planet MySQL release as yet about this new version. Release Notes.

I’d like to say I installed it, but I downloaded the Linux – Generic 2.6 (x86, 64-bit), TAR file, only to find it contains 6 rpm files. #fail, I’m using Ubuntu.

You have to scroll to the bottom of the list (another stupid thing for a generic binary choice) to get Linux – Generic 2.6 (x86, 64-bit), Compressed TAR Archive. Double #fail

Leveraging the InnoDB Plugin
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Beginning with MySQL 5.1 as an additional plugin and included by default in MySQL 5.5 the InnoDB plugin includes many performance improvements. To leverage the support of new file formats however a very important setting is necessary.

#my.cnf
[mysqld]
innodb_file_per_table

The use of innodb_file_per_table with an existing system or during an upgrade to 5.1 or 5.5 requires a complete reload of your database to use effectively. In summary.

  • Backup all InnoDB tables via mysqldump
  • Drop InnoDB tables
  • Verify InnoDB not used
  • Stop MySQL
  • Enable innodb_file_per_table & simplified innodb_data_file_path (if applicable)
  • Remove ibdata? files
  • Start MySQL
  • Create Tables
  • Reload Data
  • Verify InnoDB Operation
    • The primary

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Interesting MySQL 5.5 upgrade gotcha
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Today I discovered an interesting upgrade problem with a client migrating from MySQL 5.0 to 5.5. The client who is undertaking the upgrade reported that MySQL 5.5 did not support the DECIMAL(18,5) data type. I easily confirmed this not to be the case:

mysql> drop table if exists x;
mysql> create table x (col1 DECIMAL(18,5));
Query OK, 0 rows affected (0.01 sec)

Delving more into the issue in question, I looked at the complete CREATE TABLE statement, recreating the syntax.

mysql> drop table if exists x;
mysql> create table x ( MinValue DECIMAL(18,5));
Query OK, 0 rows affected (0.00 sec)

No problem there.

mysql> drop table if exists x;
mysql> create table x (Department INT NOT NULL, MinValue DECIMAL(18,5) NULL, MaxValue DECIMAL(18,5) NULL);
ERROR 1064 (42000): You have an error in your SQL syntax; check
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Do you use PHPMyAdmin?
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If so then were is it installed on your publicly accessible website. If the location is where the documentation states not to put it, or in other popular locations then you can easily become open to an attack. The following are apache logs of a simple hacker test to find a potential security hole on a new IP public address for a client.

My advice is never have PHPMyAdmin accessible by default. You should use HTTP authentication, firewall rules and additional security practices all to protect any level of access to your data.

78.111.81.180 - - [02/Feb/2011:05:29:24 -0500] "GET //phpmyadmin/ HTTP/1.1" 401 290 "-" "Made by ZmEu @ WhiteHat Team - www.whitehat.ro"
78.111.81.180 - - [02/Feb/2011:05:29:24 -0500] "GET //phpMyAdmin/ HTTP/1.1" 401 290 "-" "Made by ZmEu @ WhiteHat Team - www.whitehat.ro"
78.111.81.180 - - [02/Feb/2011:05:29:24 -0500] "GET //pma/ HTTP/1.1" 401
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Microsoft’s position on MySQL
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While Oracle provides no official information they are planning on improving MySQL and using as a product to compete with Microsoft SQL Server, it is rather obvious from what little information you can glean from public announcements this is a clear business goal.

Microsoft however are publicly seeking a Senior Product Manager, MySQL Compete in the Marketing department. Your goal is nothing technical, it’s all PR to dispel MySQL as a viable product. I quote “you will equip field and partners to win in competitive engagements against MySQL, and you will influence market perception in favor of Microsoft technologies.” Here is the Full job description for those that want an amusing read.

This information came from an Oracle colleague of mine based in Asia.

Welcome new Oracle ACE’s
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I am pleased to announce that the Oracle ACE program has two new MySQL inductees. These people actively contribute to the MySQL community via a varied means in an unbiased and non commercial way.

Giuseppe Maxia (aka DataCharmer) is no stranger to the MySQL community having filled a position with MySQL Inc/Sun Microsystems/Oracle Corporation in the Community team for many years. Giuseppe was an active member in the community before this position, and continues to provide great input with tools such as the MySQL sandbox and many project and code snippets on the MySQL Forge as well as many writings for the Developer zone.

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Changes in using Profiling in MySQL 5.5
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In the past I’ve used the profiling features (e.g. SHOW PROFILES) in MySQL to help with timing SQL statements, especially those in the

Out of habit I did use this to time all SQL statements however in MySQL 5.5.8 GA I've found this no longer to be representative.

As you can see, the query takes some 50+ms longer with profiling enabled, not to mention they have broken the Source_file column which I've actually used to troll the source code with.

mysql> set profiling=1;

4 rows in set (1.14 sec)
4 rows in set (1.15 sec)
4 rows in set (1.17 sec)

mysql> set profiling=0;

4 rows in set (0.37 sec)
4 rows in set (0.37 sec)
4 rows in set (0.37 sec)

Investigating further showed the cause. There appears to be some new overhead that causes profiling to log excessive amount of information.

mysql> show profile source for

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10 Newer Entries Showing entries 91 to 100 of 440 10 Older Entries

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