mysql sql big selects

mysql sql big selects  using -'mysql,select'

Hey, I've been investigating SQL_BIG_SELECTS, but the MySQL documentation so far has been pretty unhelpful. I'm looking for some insight as to preventing errors like the one below from appearing.

  ERROR 1104: The SELECT would examine too many records and probably take a very long time.
  Check your WHERE and use SET OPTION SQL_BIG_SELECTS=1 if the SELECT is ok

At how many rows does MySQL decide that a query is a "BIG SELECT"?
Will proper indexing usually solve this issue?
Is SQL_BIG_SELECTS considered a "last resort", or is it good practice?
How would someone set "SQL_BIG_SELECTS=1" in configuration (without having to execute the query)?
Are there any other alternatives worth knowing?

Thanks in advance!

asked Sep 16, 2015 by ukohale
0 votes

3 Answers

0 votes
  1. MySQL determines whether or not a query is a 'big select' based on the value of 'max_join_size'. If the query is likely to have to examine more than this number of rows, it will consider it a 'big select'. Use 'show variables' to view the value of the max join size.

  2. I believe that indexing and particular a good where clause will prevent this problem from occuring.

  3. SQL_BIG_SELECTS is used to prevent users from accidentally executing excessively large queries. It is okay to set it to ON in mysql.cnf or using the command-line option at startup.

  4. You can set SQL_BIG_SELECTS in my.cnf or at server startup. It can also be set on a session basis with 'SET SESSION SQL_BIG_SELECTS=1'.

  5. Not that I can think of. I would just check your query to make sure that you really need to use it. Our servers have it turned on by default, and max_join_size is very large.

answered Sep 16, 2015 by yashwantpinge
0 votes

As someone has post before, you can not set SQL_BIG_SELECTS on my.cnf at server startup. This kind of variable does not support that.

I had a same problem with a Symfony application showing this annoying error:

The SELECT would examine more than MAX_JOIN_SIZE rows; check your WHERE and use SET SQL_BIG_SELECTS=1 or SET SQL_MAX_JOIN_SIZE=# if the SELECT is okay

But you can increase the number of varialbe

max_join_size which is related to sql_big_selects

I was able to fix it executing a command as privileged mysql user:

# SET GLOBAL max_join_size=18446744073709551615;

Or you can include it in my.cnf because max_join_size is allowed to set up in configuration file

Well, I hope this can help someone else.

answered Sep 16, 2015 by sandeep bhadauria
0 votes

Following command works for me

SET GLOBAL max_join_size=18446744073709551615;

But what do i need to put in my.cnf file instead of the command? Btw, i'm using "5.6.12 MySQL Community Server"

answered Sep 16, 2015 by nimisha.jagtap