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Question

Poor fsync performance on DO Block Storage

Posted May 24, 2020 436 views
MySQLBlock StorageStorage

Hi there!

I have noticed very poor MySQL (InnoDB) performance on my droplet.

I am running MySQL (Percona Server) 5.6 with fine tuned config.

Database directory placed on BlockStorage.

I used fio utility to test BlockStorage disk performance and everything is ok, if I running fio as described here https://www.digitalocean.com/community/tutorials/how-to-benchmark-digitalocean-volumes . Burst performance approximately near 7500 iops, after 1 minute test it slow down to approx. 5000 iops.

As InnoDB using fsync for each commit operation to compliant data consistency I tested fio performance with fsync for each IO operation (—fsync=1). In test with fsync=1 I noticed only 50-100 iops!

Can anybody answer me why performance so poor in my case?

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vasval
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Simon501 September 29, 2020

I’ve found similar.

After some investigation (and reading up) I think the problem is that DO’s hypervisors do not use battery backed RAID controllers [would be nice if they verified this]. This means an fsync has to pysically flush to disk which is slow even on SSDs.

I see an average of about 20ms which matches your 50/sec. However, I am measuring from within the app which requires a localhost network round trip too… and I’m actually committing real data.

In a previous incarnation I used to manage database RAID arrays and one problem is that once the battery goes (which shows up as a tiny light on the controller and happens every year or two) the performance drops away.

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