FreeBSD 11.1 Beta 2 ZFS performance degradation on SSDs

[Karl Denninger]

On 6/20/2017 12:29, Caza, Aaron wrote:
>> -----Original Message-----
>> From: Karl Denninger [mailto:karl at denninger.net]
>> Sent: Monday, June 19, 2017 7:28 PM
>> To: freebsd-fs at freebsd.org
>> Subject: Re: FreeBSD 11.1 Beta 2 ZFS performance degradation on SSDs
>>
>> Just one note below...
>>
>> On 6/19/2017 19:57, Caza, Aaron wrote:
>>> Note that file /testdb/test is 16GB, twice the size of ram available in this system.  The /testdb directory is a ZFS file system with recordsize=8k, chosen as ultimately it's intended to host a PostgreSQL database which uses an 8k page size.
>> Do not make this assumption blindly.  Yes, I know the docs say to set
>> recordsize=8k but this is something you need to benchmark against your
>> actual working data set.
>>
>> MANY Postgres workloads are MUCH faster (2x or more!) if you use a
>> default page size and lz4 compression -- including one I have in
>> production and have extensively benchmarked.  The difference is NOT small..
>> ....
>>
>> zroot/ticker  compressratio         1.53x                         -
>> zroot/ticker  mounted               yes                           -
>> zroot/ticker  quota                 none                          default
>> zroot/ticker  reservation           none                          default
>> zroot/ticker  recordsize            128K                          default
>> zroot/ticker  mountpoint            /usr/local/pgsql/data-ticker  local
>> zroot/ticker  sharenfs              off                           default
>> zroot/ticker  checksum              fletcher4
>> inherited from zroot
>> zroot/ticker  compression           lz4
>> inherited from zroot
>> zroot/ticker  atime                 off
>> inherited from zroot
>>
>> You may also want to consider setting logbias=throughput.  In some cases
>> the improvement there can be quite material as well -- depending on the
>> insert/update traffic to the database in question.
>>
>> --
>> Karl Denninger
>> karl at denninger.net <mailto:karl at denninger.net>
>> /The Market Ticker/
>> /[S/MIME encrypted email preferred]/
> Thanks for the suggestions Karl.  I'll investigate further after I resolve this performance degradation issue I'm experiencing.  I recently read another FreeBSD+ZFS+PostgreSQL user's Scale15x presentation, PostgreZFS, Sean Chittenden if I recall correctly, who also advised lz4 compression + 16K page size rather than 8K with PostgreZFS.
>
> With regards to my performance woes, I was originally using PostgreSQL in my posts to freebsd-hackers at freebsd.org but started using 'dd' to remove it as a point of contention.  In attempting to resolve this issue, I tried using your patch to PR 187594 (https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=187594).  Took a bit of effort to find a revision of FreeBSD 10 Stable to which your FreeBSD10 patch would both apply and compile cleanly; however, it didn't resolve the issue I'm experiencing.
I would not have expected my PR to impact this issue.

I suspicious of a drive firmware interaction with your I/O pattern; SSDs
are somewhat-notorious for having that come up under certain workloads
that involve a lot of writes.

-- 
Karl Denninger
karl at denninger.net <mailto:karl at denninger.net>
/The Market Ticker/
/[S/MIME encrypted email preferred]/
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