A quick and easy performance improvement

Richard Lynch rich at mail.wvnet.edu
Wed Jul 26 15:38:48 IST 2006

Chris Hammond wrote:
> I might be a little thick, but what would the reason for this performance increase be the fact the / and /var are seperate partitions?
Essentially, yes.  It really comes down to how far apart on disk the 
BayesDB is from the mail queues and MailScanner temp work area.  The 
closer things are on disk the less time spent doing disk seek 
operations. That's where the benefit comes from.  A disk seek (i.e. 
moving the heads over the proper cylinder) is much much slower than any 
other operation!

Richard Lynch
Morgantown, WVa

> Chris
>>>> Richard Lynch <rich at mail.wvnet.edu> 07/26/06 9:30 AM >>> 
> I thought I'd post to the list about a change I made yesterday which 
> provided a huge boost in system's performance.
> By far the largest amount of time spent in the life of a disk I/O 
> operation is seek time.  Seek time is the amount of time it takes to 
> move the disk R/W heads from one cylinder to another.  The /var/spool 
> filesystem is where the inbound and outbound mail queues are located.  
> Note also that the Bayes database is accessed heavily when analyzing a 
> message.
> Like many installations we have our root filesystem (/) and /var 
> filesystem on separate partitions on a single hard drive.  The default 
> location for the SpamAssassin bayes database is in /root/.spamassassin/ 
> which is on the rootfs.   Moving the bayes database to 
> /var/spool/spamassassin resulted in a huge decrease in IOWait time.  In 
> our case it was an order of magnitude reduction.  For example,  IOWait 
> percentages went from 30% to 3%.  IOWait is the percentage of time the 
> processor is waiting on an I/O operation to complete.  Our mail queues 
> no longer get behind and throughput is outstanding! 
> Making the change is trivial (from root)....
> 1. Shutdown MS
> 2. mkdir /var/spool/spamassassin
> 3. mv .spamassassin/bayes* /var/spool/spamassassin/
> 4. Edit /etc/MailScanner/spam.assassin.prefs.conf and uncomment the
>     lines which define where the bayes DB is located.  Thanks Julian!  
> The lines
>     are...
>     auto_whitelist_path        /var/spool/spamassassin/auto- whitelist
>     auto_whitelist_file_mode   0600
>     bayes_path                 /var/spool/spamassassin/bayes
>     bayes_file_mode            0600
> 5. Start MS
> Just wanted to let others know and perhaps benefit from our experiences.
> Richard Lynch
> Morgantown
> --  
> --  
> This message has been scanned for viruses and
> dangerous content by MailScanner, and is
> believed to be clean.


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