slow performance with ohm/redis

[gingerlime]

Already posted this question on stackoverflow, but thought I should ask here too, just in case. Hope someone can point us in the right direction?

We're scratching our heads the last couple of days trying to understand why some things seem a bit too slow with redis/ohm on our rails project.

The gist of it is that some requests to ohm/redis take around 100-200 ms, which seem rather high considering our high-expectations of blazing-fast performance.

The command we're running looks like:

Stats::TermStats.find(term_slug: 'term_slug', user_id: 123).to_a

It seems to us that we're not doing anything extremely complex or crazy. Our profiling (using miniprofiler) of this single command so far revealed the following:

• Some of those calls complete within about 2-4 ms (is this ok/good/bad?)
• Some however take 100-200 ms (this definitely feels bad)
• Using slowlog get on the redis-client does not show anything particularly slow on redis. Most of the redis command complete within less than 20 microseconds (0.02 ms)
• Using the rails console and running a quick benchmark using the exact same slug/id in a loop, the same behaviour is observed, i.e. a few of those (same) requests seem to take considerably longer than most others

Our redis config is pretty much out-of-the-box with basically no tweaking. During testing the server is not doing much else.

Any suggestions how to improve performance / test what slows down things so much between redis and ohm/rails ??

[gingerlime]

Just in case anybody's interested, we think we have found the cause for this problem, and even a solution

TL;DR : use hiredis + tune the ruby GC parameters.

[frodsan]

Ohm 2 uses Redic instead of redis-rb. Redic uses hiredis, as a hard dependency, for the connection and for parsing the replies. It will be nice if you could try this with new versions of Ohm and re-open it to discussion if performance remains a problem. /cc @soveran can you close it?

[gingerlime]

This sounds interesting. Thanks @frodsan. Do you expect to see a difference between using Redic and redis-rb with hiredis?

[frodsan]

There is a section called "Differences with redis-rb" in the README.

[soveran]

@gingerlime Would it be OK if I we close this issue? I think it is solved in Ohm 2, but I'll wait for your +1.

[gingerlime]

I haven't had a chance to play around with Ohm 2 or redic, but sounds like this issue can be closed. Really glad to see things improving! Hope to find some time to test / compare, but not sure when.