Sharding for parallel query performance Options

[dhsieh]

There was a early post on the same topic last year
http://groups.google.com/group/mongodb-user/browse_thread/thread/aa3cd793b89ad178/d0c70444c203d164?lnk=gst&q=parallel+shard+query#.
Since I can’t add additional comments to that thread, I am posting
this follow-up with the same title. The last reply was by Eliot
Horowitz:

“Most are parallel, but a couple are still serial. We're going to be
cleaning that all up soon though: https://jira.mongodb.org/browse/SERVER-2014”

I just look at http://www.mongodb.org/display/DOCS/Choosing+a+Shard+Key
and it wrote:

"All queries work regardless of the shard key, but if mongos cannot
determine which shard that owns the data, it will send the operation
to all shards sequentially"

Also in http://www.mongodb.org/display/DOCS/Sharding+FAQ, it wrote:

"A query that keys on Y must run on all shards: if the query sorts by
X, the query will serialize over shards in X-order"

Are these Wiki pages out dated using terms like "sequentially" &
"serialize over shards" to describe current MongoDB shard parallel
query algorithm, say v2.0?

[Kristina Chodorow]

You're correct, I've updated the wiki pages to reflect the new(ish)
behavior.

On Apr 26, 2:46 pm, dhsieh <dhsi...@gmail.com> wrote:
> There was a early post on the same topic last yearhttp://groups.google.com/group/mongodb-user/browse_thread/thread/aa3c....

> Since I can’t add additional comments to that thread, I am posting
> this follow-up with the same title. The last reply was by Eliot
> Horowitz:
>
> “Most are parallel, but a couple are still serial. We're going to be
> cleaning that all up soon though:https://jira.mongodb.org/browse/SERVER-2014”
>

> I just look athttp://www.mongodb.org/display/DOCS/Choosing+a+Shard+Key

>
> and it wrote:
>
> "All queries work regardless of the shard key, but if mongos cannot
> determine which shard that owns the data, it will send the operation
> to all shards sequentially"
>

[dhsieh]

Thanks for the update. I wonder if there a more efficient way to
maintain your Wiki page with up-to-date info based on your product
release cycle?

[Kristina Chodorow]

We do try to go through stuff before each release and update things,
it's just hard to catch everything. It should be better in
forthcoming releases, we now have a dedicated documentation manager.

[dhsieh]

Instead of using Mongo user forum, do you have email of documentation
manager in 10gen we can contact dirctly in the future? Also, you may
also review the following description in
http://www.mongodb.org/display/DOCS/Sharding+FAQ#ShardingFAQ-Howdoqueriesdistributeacrossshards%3F:

"A query that keys on X and sorts on X will translate
straightforwardly to a series of queries against successive shards in
X-order"

Again, it sounds like serial rather than parallel queries.

[Barrie]

If you want to suggest a change for the documentation you can file a ticket in the Documentation project in Jira at https://jira.mongodb.org/browse/DOCS.

There's a ticket for improving the documentation on sharding here.

Hope this helps!

Barrie