Cloud Redis latency causes (vs. local redis on macbook pro) - amazon-web-services

Question

Redis can give sub millisecond response times. That's a great promise. I'm testing heroku redis and I get 1ms up to about 8ms, for a zincrby. I'm using microtime() in php to wrap the call. This heroku redis (I'm using the free plan) is a shared instance and there is resource contention so I expect response times for identical queries to vary, and they certainly do.
I'm curious as to the cause of the difference in performance vs. redis installed on my macbook pro via homebrew. There's obviously no network latency there. What I'm curious about is does this mean that any cloud redis (i.e. connecting over the network, say within aws), is always going to be quite a bit slower than if I were to have one cloud server and run a redis inside the same physical machine, thus eliminating network latency?
There is also resource contention in these cloud offerings, unless a private server is chosen which costs a lot more.
Some numbers: my local macbook pro consistently gives 0.2ms for the identical zincrby that takes between 1ms & 8ms on the heroku redis.
Is network latency the cause of this?

Answer 1

No, probably not.
The typical latency of a 1 Gbit/s network is about 200us. That's 0.2ms.
What's more, in aws you're probably on 10gbps at least.
As this page in the redis manual explains, the main cause of the latency variation between these two environments will almost certainly be a result of the higher intrinsic latency (there's a redis command to test this on any particular system: redis-cli --intrinsic-latency 100, see the manual page above) arising from being run in a linux container.
i.e., network latency is not the dominant cause of the variation seen here.
Here is a checklist (from redis manual page linked above).
If you can afford it, prefer a physical machine over a VM to host the server.
Do not systematically connect/disconnect to the server (especially true for web based applications). Keep your connections as long lived
as possible.
If your client is on the same host than the server, use Unix domain sockets.
Prefer to use aggregated commands (MSET/MGET), or commands with variadic parameters (if possible) over pipelining.
Prefer to use pipelining (if possible) over sequence of roundtrips.
Redis supports Lua server-side scripting to cover cases that are not suitable for raw pipelining (for instance when the result of a command
is an input for the following commands).