/tmp on mfs

Christopher Hilton chris at vindaloo.com
Tue Oct 20 15:20:50 UTC 2009

Reading the list yesterday I came across a little controversy about  
swap backed /tmp filesystems. I've been using this in my /etc/rc.conf

tmpmfs="YES"            # Set to YES to always create an mfs /tmp, NO  
to never
tmpsize="1g"            # Size of mfs /tmp if created
tmpmfs_flags="-S -o async,noexec"       # Extra mdmfs options for the  
mfs /tmp

To mount /tmp on a swap backed filesystem. I've been assuming that  
data stored in the /tmp directory was held in RAM and then written to  
the swap space only when the system had a more pressing need for the  
RAM. I typically configure my systems with swap == 2 * RAM or more.  
And on the systems in question I have at least 1Gb of RAM. I was  
hoping to  use this trick to enhance the performance of the postgresql  
database (temp_tablespace=/tmp/pgsql/....) Is my assumption about  
where the data in a temporary file is stored incorrect?

-- Chris

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