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From Alex Popescu <al...@datastax.com>
Subject Re: Multi-node cluster-aware client connection
Date Wed, 11 Sep 2013 16:42:20 GMT
Paul,

Out of curiosity, what language is your driver for?


On Wed, Sep 11, 2013 at 9:20 AM, Paul LeoNerd <leonerd@leonerd.org.uk>wrote:

> Having got the first stage of my client connector module nicely working
> to a single node, I'm now looking at how to make it cluster-aware,
> maintaining multiple connections for reliability and load-spreading.
> What are some good strategies to take here?
>
> My current plan involves connecting to a (randomly chosen from a list?)
> seed node, to query the list of peers in the cluster, then make a
> selection of some number of those to be "primary" nodes, and some more
> as "backup" nodes. The primary nodes will be used to spread actual
> query load around, the backups sitting idle simply as a fast way to
> failover to some known-working connection if a primary falls over. By
> registering an interest in topology and status change messages, the
> client can keep the list of available nodes up-to-date.
>
>  1. What is a good way to handle prepared statements here? Should they
>     be prepared on all the (primary/all?) nodes, or just one? Some
>     applications I could imagine having just a handful of heavily-used
>     prepared statements, so they'd become a hotspot on one node if it
>     wasn't spread around. But then what to do as new nodes become
>     elected as primaries? Should they be prepared eagerly on
>     connection? Lazily at next use?
>
>  2. Secondly; what are suggested ways to actually spread load among the
>     primaries? I could imagine a simple round-robin, or something more
>     fancy involving picking the node with the fewest outstanding
>     requests, or the one on which we've been responsible for the least
>     processing time recently, or something else... Do client libraries
>     generally provide a selection of these mechanisms, or just pick one?
>
> --
> Paul "LeoNerd" Evans
>
> leonerd@leonerd.org.uk
> ICQ# 4135350       |  Registered Linux# 179460
> http://www.leonerd.org.uk/
>



-- 

:- a)


Alex Popescu
Sen. Product Manager @ DataStax
@al3xandru

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