What to do if the auto-increment value reaches its limit?

问题

I am doing a little research for a problem that might occur someday. Lets say you have an InnoDB MySQL table with an id and a name field. the id field has BIGINT(20) and is AUTO_INCREMENT plus its the primary key.

What do you do in a case that this table is full which means we have reached the limit on the id and no auto increment number can be generated anymore.

回答1:

Let's assume a table structure like:

CREATE TABLE `tbl` (
    `id` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT,
    PRIMARY KEY (`id`)
);

and INSERT queries like:

INSERT INTO tbl(id) VALUES (NULL);

In the real code there are also other columns in the table and they are also present in the INSERT query but we can safely ignore them because they don't bring any value to this specific issue.

When the value of column id reaches its maximum value no more rows can be inserted in the table using the query above. The next INSERT fails with the error:

SQL Error (167): Out of range value for column 'id'.

If there are gaps in the values of the id column then you can still insert rows that use values not present in the table but you have to specify the values for id in the INSERT query.

Anyway, if the type of your AUTO_INCREMENT column is BIGINT you don't have to worry.

Assuming the code inserts one million records each second (this is highly overrated, to not say impossible), there are enough values for the id column for the next half of million years. Or just 292,277 years if the column is not UNSIGNED.

I witnessed the behaviour on a live web server that was using INT(11) (and not UNSIGNED) as the AUTO_INCREMENTed PK for a table that records information about the visits of the web site. It failed in the middle of the night, after several years of running smoothly, when the visits number reached 2^31 (2 billions and something).

Changing the column type from INT to BIGINT is not a solution on a 2-billion records table (it takes ages to complete and when the system is live, there is never enough time). The solution was to create a new table with the same structure but with BIGINT for the PK column and an initial value for the AUTO_INCREMENT column and then switch the tables:

CREATE TABLE `tbl_new` (
    `id` BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
    PRIMARY KEY (`id`)
) AUTO_INCREMENT=2200000000;

RENAME TABLE `tbl` TO `tbl_old`, `tbl_new` TO `tbl`;

回答2:

tinyint: 1 byte, -128 to +127 / 0 to 255 (unsigned)
smallint: 2 bytes, -32,768 to +32,767 / 0 to 65,535 (unsigned)
mediumint: 3 bytes, -8,388,608 to 8,388,607 / 0 to 16,777,215 (unsigned)
int/integer: 4 bytes, -2,147,483,648 to +2,147,483,647 / 0 to 4,294,967,295 (unsigned)
bigint: 8 bytes, -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 / 0 to 18,446,744,073,709,551,615 (unsigned)

Did you think this number is a small number ? maybe you will be dead before you achieve this number

来源：https://stackoverflow.com/questions/46365450/what-to-do-if-the-auto-increment-value-reaches-its-limit

标签

mysql

auto-increment

bigint