Yay! My first blog post! As long as at least 1 person finds it useful, I’ve done my job. 😉 Recently, one of my long-term clients was noticing that while their INSERTs were succeeding, a particular column counter was not incrementing. A quick investigation determined the column was of type int(11) and they had reached the maximum value of 2147483647. We fixed this by using pt-online-schema-change to change the column to int(10) unsigned, thus allowing values up to 4294967295.

My client was now concerned about all his other integer-based columns and wanted me to check them all. So I wrote a quick-n-dirty script in Go to check all integer-based columns on their current value compared to the maximum allowed for that column type.

You can find the full source code in my git repo.

Here’s a quick overview; the code is pretty simple.

First we connect to MySQL and verify the connection:

Next, we query the information_schema.columns table for the names of all integer-based columns and calculate what their maximum value can be (credit for the clever SQL goes to Peter Boros).

Now that we have this list of columns to check, we simply loop over this result set, get the MAX() of each column and print a pretty report.

There are more options to the app that allow you to silence some of the verbosity and to only print report lines where the value-to-max ratio is > a user-defined threshold. If you have frequently changing schemas, this should allow you to cron the app and only receive email reports when there is a potential problem. Otherwise, this tool could be useful to run once a month/quarter, just to verify things are in good standing.

Like I said before, hopefully this helps at least 1 person catch a potential problem sooner rather than later.

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Shlomi Noach

Please also consider using common_schema’s auto_increment_columns view: https://common-schema.googlecode.com/svn/trunk/common_schema/doc/html/auto_increment_columns.html
or just use this query: http://code.openark.org/blog/mysql/checking-for-auto_increment-capacity-with-single-query

or otherwise use this openark-kit tool: http://openarkkit.googlecode.com/svn/trunk/openarkkit/doc/html/oak-show-limits.html

We’re using the common_schema view when monitoring our servers. We’re checking this view on a couple slaves (they all resolve the same obviously, and we don’t want to do I_S queries on the master if we don’t have to). We have threshold alerts on the AUTO_INCREMENT capacity and live quietly ever after.

Charl Retief

On you first blog post, let me make my first ever comment.

On this topic it is also worth mentioning that MySQL has this obscure feature it called “Procedure Analyse”. It gives you current data type usage min and max values, null frequency ect. as well as optimal suggested field size.
http://dev.mysql.com/doc/refman/5.6/en/procedure-analyse.html

You could very easily use this to get this information without any external scripting. Like:
SELECT * FROM table1 PROCEDURE ANALYSE(10, 2000);

Or this stored proc that does it for a whole db:

CREATE PROCEDURE table_field_size_analyse(IN $database VARCHAR(255))
BEGIN

DECLARE $table_name VARCHAR(255);

DECLARE $table_cursor CURSOR FOR SELECT TABLE_NAME FROM information_schema.TABLES WHERE TABLE_SCHEMA = $database;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET $table_name = NULL;

OPEN $table_cursor;
table_loop: LOOP

FETCH $table_cursor INTO $table_name;

IF $table_name IS NULL
THEN
LEAVE table_loop;
END IF;

SET @dsql = CONCAT(‘SELECT * FROM ', $database, '.', $table_name , ' PROCEDURE ANALYSE(10, 2000);’);

PREPARE stmt1 FROM @dsql;
EXECUTE stmt1;
DEALLOCATE PREPARE stmt1;

END LOOP;
CLOSE $table_cursor;

END

Charl Retief

Matthew,

You are absolute correct, the “Procedure Analyse” route is horribly slow due to the full table scans. Definitely not something you want to use on production systems. You method is more suited for your described work case.

Ike Walker

I use common_schema for this. If you have common_schema installed, the auto_increment_columns view exposes this data and is simpler to work with than information_schema.

I also blogged about this a while back: http://mechanics.flite.com/blog/2012/07/16/monitoring-auto-increment-capacity-in-mysql/

r937

you say at the outset that you wanted to change all INT(11) to INT(10) UNSIGNED

sweet, but the numbers in parentheses are huge red herrings, especially as you seem to want to make the number smaller by 1

you could just as easily have said INT(937) UNSIGNED for all the difference it makes

Fadi (itoctopus)

@r937,

I think you’re confusing the x in INT(x) for the number of bits/bytes. You can read more about this here: http://stackoverflow.com/questions/7552223/int11-vs-intanything-else

@Matthew,

You are probably the first person I know of that uses Go for something that is not experimental. Oh, and congratulations on your new post. I love this blog and I visit it regularly.

r937

@Fadi — me? me confused? on the contrary, i was trying to point out that the number in parentheses is a red herring

http://en.wikipedia.org/wiki/Red_herring

“… something that misleads or distracts from the relevant or important issue”

Fadi (itoctopus)

@r937,

Sorry – my bad. I seem to have skipped your second line in your original comment.

Yogesh Malik

Hi,

We also faced the same situations last year which we weren’t aware of and never expected but it happened and it took us one hour to identify the problem. It was embarrassing moment as service was down for almost 1 hour.

Thanks Matthew for more insight.

Flimm

Another way to catch these problems is to pay attention to MySQL warnings, by logging them.