# tmp\_table\_size, what is too large?

**URL:** <https://forums.percona.com/t/tmp-table-size-what-is-too-large/1496>\
**Category:** Other MySQL® Questions\
**Created:** [September 3, 2010, 8:52am UTC](https://forums.percona.com/t/tmp-table-size-what-is-too-large/1496 "2010-09-03T08:52:18Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![micromatikal](https://avatars.discourse-cdn.com/v4/letter/m/49beb7/32.png) [@micromatikal](https://forums.percona.com/u/micromatikal)\
**Post date:** [September 3, 2010, 8:52am UTC](https://forums.percona.com/t/tmp-table-size-what-is-too-large/1496/1 "2010-09-03T08:52:18Z")

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On this particular DB server we have some very very large tables, and large temp tables being created (many GB in some cases). However I am apprehensive about turning the max\_heap\_table\_size and tmp\_table\_size up too far… We have a TON of free memory on the system (like 50 GB unused for example) and want many more tables to be created in memory. How far can I safely go with these values?

Here is what it looks like now:

Current max\_heap\_table\_size = 512 M  
Current tmp\_table\_size = 512 M  
Of 282433 temp tables, 44% were created on disk  
Perhaps you should increase your tmp\_table\_size and/or max\_heap\_table\_size to reduce the number of disk-based temporary tables

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**Author:** ![gmouse](https://avatars.discourse-cdn.com/v4/letter/g/b9e5f3/32.png) [@gmouse](https://forums.percona.com/u/gmouse)\
**Post date:** [September 3, 2010, 4:19pm UTC](https://forums.percona.com/t/tmp-table-size-what-is-too-large/1496/2 "2010-09-03T16:19:31Z")

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Your values are insanely high. One reason reason tables are created on disk is having text columns:  
[http://dev.mysql.com/doc/refman/5.0/en/memory-storage-engine](http://dev.mysql.com/doc/refman/5.0/en/memory-storage-engine) .html  
"MEMORY tables cannot contain BLOB or TEXT columns. "