MySQL Bugs: #53119: request to make dynamic tmpdir option

Bug #53119	request to make dynamic tmpdir option
Submitted:	23 Apr 2010 16:04	Modified:	27 May 2010 19:34
Reporter:	Pavel Zheltouhov	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Options	Severity:	S4 (Feature request)
Version:	any	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	disk full, RAM, ramdrive, Repair, tmpdir, tmpfs

Description:
We use tmpdir option pointed to tmpfs linux filesystem in RAM for fast sorting in some queries. Size of 256mb necessary in most cases.
Sometimes we need repair big tables and that huge temporary file does get in tmpfs due limitation. So we need stop server, change tmpdir option, than start server again.
If we can change tmpdir option at runtme, this annoying behavior can be overcome.

How to repeat:
mysql> set global tmpdir='c:/';
ERROR 1238 (HY000): Variable 'tmpdir' is a read only variable

Thank you for the feature request. 

I wonder if tmpdir pointing to symbolic link and redefinition of symbolic link can be used as a workaround, at least in some cases.

I wrote some scripts for make tmp in memory at mysql startup (and check big tables).
I run mysql with disk tmpdir, after 600 seconds run script to remove symlink and create symlink to tmpfs.
How to make sure for tmpdir in memory ?

#lsof | grep /var/lib/tmpmysql 
display nothing 
but  lsof | grep myhardtmp display this :
mysqld    15108       mysql    4u      REG                8,5          0      46814 /myhardtmp/ibuAlcnG (deleted)
mysqld    15108       mysql    5u      REG                8,5          0      46825 /myhardtmp/ibPEPXHp (deleted)
mysqld    15108       mysql    6u      REG                8,5          0      46826 /myhardtmp/ib9qXJ28 (deleted)
mysqld    15108       mysql    7u      REG                8,5          0      46827 /myhardtmp/ibHxtjsS (deleted)
mysqld    15108       mysql   11u      REG                8,5          0      46828 /myhardtmp/ibzOtdZB (deleted)

Is it works or not ?

When this variable is dynamic it should also replicate.

This looks like a duplicate of Bug #50291