Percona Server has implemented per-query variable statement support in version 5.6.14-62.0. This feature provides the ability to set variable values only for a certain query, after execution of which the previous values will be restored. Per-query variable values can be set up with the following command:
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mysql> SET STATEMENT <variable=value> FOR <statement>; |
Example:
If we want to increase the sort_buffer_size value just for one specific sort query we can do it like this:
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mysql> SET STATEMENT sort_buffer_size=100000 FOR SELECT name FROM name ORDER BY name; |
Using the per-query variable statements with Statement Timeout feature
Percona Server has implemented a statement timeout feature (This feature with some changes was ported from Twitter MySQL patches). This feature can be used to limit the query execution time by specifying the timeout value in the max_statement_time variable. After the specified number of miliseconds is reached the server will attempt to abort the statement and return the following error to the client:
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ERROR 1877 (70101): Query execution was interrupted, max_statement_time exceeded |
Following example shows how to limit the execution time for a specific query by using per-query variable statements with Statement Timeout feature:
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mysql> SET STATEMENT max_statement_time=1000 FOR SELECT name FROM name ORDER BY name; |
This feature isn’t just limited to specifying one variable, we can provide more than one if we want to. Following example will both increase the sort_buffer_size value and limit the execution time:
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mysql> SET STATEMENT sort_buffer_size=100000, max_statement_time=1000 FOR SELECT name FROM name ORDER BY name; |
Is their anyway to limit the value that can be set for a per-query variable?
What about MySQL? is it implemented on new version or not?
HI,
It is not quite clear to me how this works. Will the new set statement execute the query, or will it just tell the server to set the variable each time (or only the first?) the specified statement is executed?
@Michael Rikmas
There is no way to limit the per-query variable setting.
@Saeid
At the moment MySQL doesn’t have this implemented.
@Øystein
New statement will execute the query with the variables set to the specified values for the duration of that statement. Think of such statements as plain SELECT name FROM name … that happen to have some local modifiers to that statement.
Oystein,
I agree with you syntax is a bit confusing. I would rather see something like SELECT … USING VARIABLES … but it was easier from parser standpoint to implement it this way. If you implement similar feature in MySQL with different syntax I will not be offended.
Michael,
Currently limits are not enforced though it would be right to have them as we support minimum and maximum values for variables as set by users
https://www.percona.com/doc/percona-server/5.6/management/expanded_program_option_modifiers.html