Re: [tlug] Possible command to boost to laptop performance

[Darren Cook <darren@example.com>]

Dave wrote:
> Recently, I came across this simple command which seems to help. 
> Actually, it helps a heck of a lot, though it does raise questions. 
> sudo sh -c "sync; echo 3 > /proc/sys/vm/drop_caches"

Thanks for this tip and the discussion that followed; it was educational.

I've been trying to track down why a database import process was so much
slower on an ubuntu 10.04 machine than a ubuntu 8.04 machine. Both
software RAID, 4 cores, plenty of memory, etc.

I found a couple of speedups, and as the first is general I thought it
would be of interest. Here is the sound bite: ext4 writes much slower
than ext3.

Eh, you cry? It didn't say that on the packet?! What changed is (in the
default configuration) ext4 is safer than ext3, but the trade-off is
that writes are slower. If you were happy with the peace-of-mind-level
of ext3 (I was), then you can get that by switching off "barrier" (see
[1][2]).

Intial DB import speed (this was an immediate rerun, so maximum benefit
of caching): 3m 42s

I then added barrier=0 to my /etc/fstab. Straight after a reboot it
improved to: 1m 57s
A re-run (a few days later, so maybe a little help from cache): 1m 27s

I then tried a few mysql improvements, and it went down to 1m 6s (1m 30s
after a reboot). Not great, but not to be sniffed at.

While typing this up I noticed I didn't have noatime on that partition.
So I added that, another reboot, but (as expected, because noatime makes
reads quicker, not writes) no improvement: 1m 38s (1m 10s when run again).

So, for this particular application:
 * getting rid of barrier: 200-250% speed-up
 * mysql tweaking: 30-40% speed-up

Darren


[1]: http://lwn.net/Articles/283161/

[2]: http://ubuntuforums.org/showthread.php?t=1313834

[3]: Added these to /etc/mysql/my.cnf:
innodb_buffer_pool_size = 256M
innodb_additional_mem_pool_size = 32M
innodb_log_file_size = 64M
innodb_log_buffer_size = 8M

(When changing log_file_size you have to stop mysql, go to
/var/lib/mysql/ and delete the two ib_logfile files, then start mysql.)



-- 
Darren Cook, Software Researcher/Developer

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