问题
For an application written in Scala I'm looking for the 'best' database system for the following requirements:
- Good support for queries like: For a node find all connected nodes, all nodes connected via another node with value 'somevalue'
- Available as a cloud service for 0$ for low volumes of data
- Good community support and documentation
回答1:
Most probably you are trying to store a graph on your database.
There are graph databases especially created for storing nodes and connecting nodes with vertices (in your terms, values). http://en.wikipedia.org/wiki/Graph_database#Graph_database_projects
I'm afraid, there are no free options offered in the cloud for free. You should buy a VPS, Amazon EC2 instance, Windows Azure instance or whatsoever to host your database. Nothing comes free these days.
Among the graph databases, my choice would be neo4j, it has a good support, documentation, community and it is especially designed for usage with Java (and Scala, of course). However I heard that orientdb and vertexdb are also good for that.
回答2:
Good support for queries like: For a node find all connected nodes, all nodes connected via another node with value 'somevalue' Good community support and documentation
Postgres is quite adequate if you only need to find nodes within a neighborhood, in that it supports recursive queries.
Assuming you've an oriented graph of nodes (id, parent_id, col), this allows to write:
with rec_nodes as (
select id,
col,
1 as depth
from nodes
where parent_id = :id
union all
select nodes.id,
nodes.col,
rec_nodes.depth + 1 as depth
from nodes
join rec_nodes on rec_nodes.parent_id = nodes.id
where depth < :depth
)
select id
from rec_nodes
where col = :col;
The above will perform very well as long as the :id and :depth constraints are within the with statement (when not, it'll build the whole graph, and you definitely don't want that to occur).
Available as a cloud service for 0$ for low volumes of data
Not cloud, nor $0, but very cheap here. (Last I checked, the basic VPS offered Postgres on a shared server. And the whole thing is run by one of the Postgres founders.)
Be wary when hosting a DB in the cloud directly.
来源：https://stackoverflow.com/questions/6317044/whats-the-right-database-system-for-this