MySQL tmpdir in ramdisk (limitted size)

[postcd]

Hello,

i learned in these articles:

MySQL tmpdir on RAM-disk

http://2bits.com/articles/reduce-your-servers-resource-usage-moving-mysql-temporary-directory-ram-disk.html

that one can set mysql to swap? files into RAM instead on HDD.

I am considering to make tmpfs for tempdir, but what will happen if space is not enough? tmpdir option can have multiple path, but as I understand it, those paths will be looped, so when query is executed it gets one path (tmpfs for example) and work with that. If space is not enough… I don’t see any information that next dir will be used instead. And if next is not used, then what will happen when ramdisk space is too small?

Is there some way to measure current usage of tmp space, so to create my tmpfs accordingly?

[blastermaster]

100% calc tmp usage not possible, but for example size of the biggest table or biggest indexes.