简单的InnoDB表上的简单MySQL INSERT查询需要40 + ms

Question

I'm wondering what's exact cause that makes insert queries on mysql/innodb to last at least 40ms on machine with fairly strong cpu. "Equivalent" query runs <10ms on same MyISAM table (tables are without any foreign keys). Timings are from MySQL console.

This is "as simple as possible" db structure for reproduction.

CREATE TABLE `test_table_innodb` (
  `id` int NOT NULL AUTO_INCREMENT,
  `int_column` int NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

CREATE TABLE `test_table_myisam` (
  `id` int NOT NULL AUTO_INCREMENT,
  `int_column` int NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

I'm running same query from mysql console (which auto-commits transactions in case of InnoDB). No other queries are executed on machine at the time and the results are:

 mysql> insert into test_table_myisam (int_column) values (5);
 Query OK, 1 row affected (0.00 sec)

 mysql> insert into test_table_innodb (int_column) values (5);
 Query OK, 1 row affected (0.06 sec)

Is transaction overhead making query to run that longer against InnoDB table? Or?

Answer 1

There are three aspects that to be considered with each auto-committed INSERT

ASPECT #1. Overhead

InnoDB supports MVCC and Transaction Isolation as an ACID-compliant storage engine. In order to accommodate this, a copy of a row before changes are committed is written into the Undo Tablespace section of the System Tablespace file ibdata1 . What would be written if you are running an INSERT? A copy of a blank row . That way, a rollback simply removes the attempt to INSERT. When an INSERT in committed, the copy of the blank in the Undo Tablespace is expunged.

ASPECT #2. Clustered Index

For every InnoDB table, there exists an internal default row index called gen_clust_index . This is created regardless of the presence or absence of a PRIMARY KEY. Since your table has a PRIMARY KEY of id, the gen_clust_index is constructed to be associated with the row containing a unique id field.

ASPECT #3. Configuration

Believe it or not, there are times when MySQL 4.1 out-of-the-box is faster than MySQL 5.5. Sounds shocking, doesn't it? Percona actually benchmarked several versions of MySQL and found this to be the case.

I wrote about this in DBA StackExchange before

• Why mysql 5.5 slower than 5.1 (linux,using mysqlslap) (Nov 24, 2011)
• Query runs a long time in some newer MySQL versions (Oct 05, 2011)
• Multi cores and MySQL Performance (Sep 20, 2011)
• How do I properly perform a MySQL bake-off? (Jun 19, 2011)

Answer 2

The CPU is not the factor here. The factor is the disk . In innodb the command need to be write to log , so if the log disk is the same disk or disk is not fragment or disk is slow than you will have a big difference.