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From Tabeth Nkangoh <tab...@tabeth.com>
Subject Re: CouchDB and future
Date Thu, 11 Jul 2019 15:43:43 GMT
Hello all,


After reading the documentation <https://docs.couchdb.org/en/2.2.0/cluster/sharding.html>
and this thread I propose the following formula to document officially for determining the
Q and N values.


To start, as currently documented, N should be set to the number of nodes. This much is straightforward
and is documented more or less correctly.



For Q, it should equal the amount of cores at a minimum. So, for the cheapest Digital Ocean
droplet, which 1GB of RAM and 1vCPU, Q should be set to 1 by the user. In the case that each
core is sufficiently beefy, e.g. Intel Xeon or turbo clocked AMD EPYC 7000 2 should be added.
2 is an arbitrary value but reflects the reality that from what I can tell a dramatically
higher clock speed benefits CouchDB performance AFAIK (I'm not sure if this benefit is a constant
or a multiplier, but I doubt it is a multiplier simply due to the diminishing returns seen
in increased clock speed).


To summarize the following table can be used (for example):


CPU Cores       CPU Clock Speed         Q Value
1       Low     1
2       Low     2
2       High    4
3       High    5
4       Low     4


Does anyone have any qualms with this as a general guide to give users in determining the
Q value they should set for their CouchDB instance? If not I can submit a PR soon on this
(have to figure out how to create a new reference for one that's currently open first).

Tabeth

________________________________
From: Joan Touzet <wohali@apache.org>
Sent: Thursday, July 11, 2019 11:17 AM
To: dev@couchdb.apache.org
Subject: Re: CouchDB and future

On 2019-07-11 8:05, ermouth wrote:
>> to help with the documentation step
>
> Probably. Please give me a hint what you need.

What default settings right now are wrong for a system with low RAM, low
CPU, and slow disk - such as a RaspberryPi v1, or a $15/mo AWS server?

-Joan


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