Re: PostgreSQL vs Mongo

On Wed, Oct 16, 2013 at 8:30 AM, CS DBA <cs_dba(at)consistentstate(dot)com> wrote:

> All;
>
> One of our clients is talking about moving to Mongo for their
> reporting/data mart. I suspect the real issue is the architecture of their
> data mart schema, however I don't want to start pushing back if I can't
> back it up.
>

You want to find out what the issues are before making your pitch. Get
specifics.

>
> Anyone have any thoughts on why we would / would not use Mongo for a
> reporting environment.
>
> what are the use cases where mongo is a good fit?
>

The argument for NoSQL in reporting is where the variety of data makes
traditional reporting difficult. This is a niche case, and not a typical
data mart.

> what are the drawbacks long term?
>

If you use the wrong tool for the job. you are going to find yourself coded
into corners. The tradeoff is that if you allow data variety on the way
in, you can't ensure simple mathematical transformation of that data to be
meaningful on the way out. This means that the precision of your answers
goes down once you eliminate schemas. Where you don't have to, you should
not go with a NoSQL solution for reporting.

After all, reporting really is the forte of SQL and has been for a long
time.

> is mongo a persistent db or simply a big memory cache?
> does mongo have advantages over Postgres hstore?
>

I assume Mongo docs can be nested JSON? Also you have some intraquery
parallelism at least between nodes. The latter can be solved with careful
use of Postgres-XC. The former would make XML on PostgreSQL a better
comparison.

In general these things need to be details-oriented. It is critically
important to find out if they are considering it due to hype or whether
they have real reasons for the comparison. Maybe in some cases, NoSQL
options may be better, but these are relatively rare, particularly in
analytic environments.

--
Best Wishes,
Chris Travers

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