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From Robert Coli <rc...@eventbrite.com>
Subject Re: Disabling the write ahead log with 2 data centers?
Date Fri, 23 Jan 2015 21:48:37 GMT
On Fri, Jan 23, 2015 at 9:59 AM, Kevin Burton <burton@spinn3r.com> wrote:

> The WAL (and walls in general) impose a performance overhead.
>
> If one were to just take a machine out of the cluster, permanently, when a
> machine crashes, you could quickly get all the shards back up to N replicas
> after a node crashes.
>

It depends a bit on your consistencylevel and frequency of repair, and (as
Rusty says) how much you care about your data. But why take the machine
out? Just have it rejoin... taking it out means you lower the "unique
replica count" by one and lose any data that for whatever reason was only
propagated there.

But yes, the overhead of the commit log is why the durable_writes:false
cassandra.yaml option exists. Some people are ok with losing everything
that was in a memtable on only the single crashed node; most are not, and
should not disable the commit log.

=Rob

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