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Asked: 2026-06-03T23:57:19+00:00

I have this simple query: INSERT IGNORE INTO beststat (bestid,period,rawView) VALUES ( 4510724 ,

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I have this simple query:

INSERT IGNORE INTO beststat (bestid,period,rawView) VALUES ( 4510724 , 201205 , 1 )

On the table:

CREATE TABLE `beststat` (
 `bestid` int(11) unsigned NOT NULL,
 `period` mediumint(8) unsigned NOT NULL,
 `view` mediumint(8) unsigned NOT NULL DEFAULT '0',
 `rawView` mediumint(8) unsigned NOT NULL DEFAULT '0',
 PRIMARY KEY (`bestid`,`period`),
) ENGINE=InnoDB AUTO_INCREMENT=2020577 DEFAULT CHARSET=utf8

And it takes 1 sec to completes.

Side Note: actually it doesn’t take always 1sec. Sometime it’s done even in 0.05 sec. But often it takes 1 sec

This table (beststat) currently has ~500’000 records and its size is: 40MB. I have 4GB RAM and innodb buffer pool size = 104,857,600, with: Mysql: 5.1.49-3

This is the only InnoDB table in my database (others are MyISAM)

ANALYZE TABLE beststat shows: OK

Maybe there is something wrong with InnoDB settings?

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1 Answer

  1. Editorial Team

    So you have two unique indexes on the table. You primary key is a autonumber. Since this is not really part of the data as you add it to the data it is what you call a artificial primary key. Now you have a unique index on bestid and period. If bestid and period are supposed to be unique that would be a good candidate for the primary key.

    Innodb stores the table either as a tree or a heap. If you don’t define a primary key on a innodb table it is a heap if you define a primary key it is defined as a tree on disk. So in your case the tree is stored on disk based on the autonumber key. So when you create the second index it actually creates a second tree on disk with the bestid and period values in the index. The index does not contain the other columns in the table only bestid, period and you primary key value.

    Ok so now you insert the data first thing myself does is to ensure the unique index is always unique. Thus it read the index to see if you are trying to insert a duplicate value. This is where the slow down comes into play. It first has to ensure uniqueness then if it passes the test write data. Then it also has to insert the bestid, period and primary key value into the unique index. So total operation would be 1 read index for value 1 insert row into table 1 insert bestid and period into index. A total of three operations. If you removed the autonumber and used only the unique index as the primary key it would read table if unique insert into table. In this case you would have the following number of operations 1 read table to check values 1 insert into tables. This is two operations vs three. So you do 33% less work by removing the redundant autonumber.

    I hope this is clear as I am typing from my Android and autocorrect keeps on changing innodb to inborn. Wish I was at a computer.

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