Upper limit of views?

[Sean Clark Hess <se...@gmail.com>]

I love Couch, but I keep running into things I don't understand, and seem
like they would cause problems in the long run.

One of those is the idea that you dump a whole bunch of related information
into the same database, then build design documents and views for it. I
believe the docs say normally you have one design document per application?

Under the hood then, don't we have to run a map function on each document in
the database for each view in each design document? Eventually, it seems
quite reasonable to expect that I'd have 20 or so views of the same data.
Wouldn't that slow down inserts a lot? What is the practical upper limit of
views?

Write speed is pretty important for one part of our system - should I put
that data in another database so it doesn't get slowed down by the rest of
the data's views?

Thanks!

Re: Upper limit of views?

[Troy Kruthoff <tk...@gmail.com>]

Sean,

Your write speed will not be affected, as couch will not update the  
view until the view is accessed.

Troy


On Jan 25, 2010, at 8:30 AM, Sean Clark Hess wrote:

> I love Couch, but I keep running into things I don't understand, and  
> seem
> like they would cause problems in the long run.
>
> One of those is the idea that you dump a whole bunch of related  
> information
> into the same database, then build design documents and views for  
> it. I
> believe the docs say normally you have one design document per  
> application?
>
> Under the hood then, don't we have to run a map function on each  
> document in
> the database for each view in each design document? Eventually, it  
> seems
> quite reasonable to expect that I'd have 20 or so views of the same  
> data.
> Wouldn't that slow down inserts a lot? What is the practical upper  
> limit of
> views?
>
> Write speed is pretty important for one part of our system - should  
> I put
> that data in another database so it doesn't get slowed down by the  
> rest of
> the data's views?
>
> Thanks!

Re: Upper limit of views?

[Paul Davis <pa...@gmail.com>]

On Mon, Jan 25, 2010 at 11:30 AM, Sean Clark Hess <se...@gmail.com> wrote:
> I love Couch, but I keep running into things I don't understand, and seem
> like they would cause problems in the long run.
>
> One of those is the idea that you dump a whole bunch of related information
> into the same database, then build design documents and views for it. I
> believe the docs say normally you have one design document per application?
>
> Under the hood then, don't we have to run a map function on each document in
> the database for each view in each design document? Eventually, it seems
> quite reasonable to expect that I'd have 20 or so views of the same data.
> Wouldn't that slow down inserts a lot? What is the practical upper limit of
> views?
>
> Write speed is pretty important for one part of our system - should I put
> that data in another database so it doesn't get slowed down by the rest of
> the data's views?
>
> Thanks!
>

Couple points:

* One design doc per app is somewhat misleading. I prefer the more
general form of "One design doc per group of related views and
supporting code." The term "application" is kind of hard to pin down
exactly so its hard to use it in a rule of thumb style quote.

* Generally speaking, views won't slow down inserts because views
aren't updated until you query them.

* In terms of limits, its hard to say other than 20 isn't approaching
it. I'd expect at least thousands depending on access patterns on so
on. And the first limit that comes to mind would be the number of open
file descriptors.

* Its hard to know when you should split data between databases versus
not. I would say that you'd probably just need to measure for your
expected workload to see how it shakes out.

HTH,
Paul Davis