xtrabackup seems to ignore the throttle setting

[Dan Rogart]

Hi-

I am attempting to run xtrabackup with '--throttle=150', but it
doesn't seem to actually limit the iops on the server.

I am using this version of xtrabackup: ./xtrabackup Ver 1.0 Rev 113
for 5.0.84 unknown-linux-gnu (x86_64). It's backing up a mysql 5.0.67
instance, running the stock innodb storage engine. My OS is Centos
5.2.

As this is a test server, the only i/o activity on it is from
xtrabackup. There is no database activity.

I run innobackupex with these parameters:

/usr/bin/perl /var/backups/xtrabackup/bin/innobackupex --port=3306 --
user=mysql_user --password=mysql_password --no-timestamp --ibbackup=/
var/backups/xtrabackup/bin/xtrabackup --slave-info --throttle=150 /
var/backups/xtrabackup/archive/20100317_194844 2>> /var/backups/
xtrabackup/logs/20100317_194844.log

Which then calls xtrabackup like this:

/var/backups/xtrabackup/bin/xtrabackup --backup --suspend-at-end --
target-dir=/var/backups/xtrabackup/archive/20100317_194844 --
throttle=150

It looks to me like the throttle settings are correctly passed to
xtrabackup, but iostat output shows well over 150 iops consistently
during the backup:

(from iostat -x 5)
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz
avgqu-sz await svctm %util
cciss/c0d0 130.60 30.00 503.00 609.20 111867.20 111944.20
201.23 4.37 3.93 0.52 58.34
cciss/c0d0 130.20 37.20 498.60 629.60 111448.00 111737.80
197.82 4.53 4.01 0.52 58.90
cciss/c0d0 122.16 40.12 464.07 572.06 103862.67 104067.27
200.68 4.63 4.47 0.59 61.04

Again, the only i/o activity on this server is from the xtrabackup
job.

Any idea why it's not actually throttling its i/o ? Hopefully I'm
doing something silly that is keeping it from working.

Thanks much,
Dan Rogart

[Dan Rogart]

Based on our testing it looks like the throttle setting actually ends
up throttling reads to about (throttle value * 1M/sec).

For example, using throttle = 7 we see about 7-8 M/sec in reads on our
test server.

One further issue is that using the 'stream' parameter ignores the
throttle value. This is documented, so my fault for not realizing
that.

I think we'll be using 'pv' to throttle the stream throughput as
described here: http://www.mysqlperformanceblog.com/2009/05/20/hint-throttling-xtrabackup/
. We want to stream the data to gzip anyway, so this seems like the
way to proceed. So far results are as expected in testing.

Thanks much - xtrabackup is a great product.

-Dan Rogart

[Vadim Tkachenko]

Dan,

Thanks!

Good to see you resolved it :)

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Vadim Tkachenko, CTO, Percona Inc.
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