scalable persistence for startup
this is my fist post on SO, so far I've been just lurking around... GREAT site!!<br/>
So here is my question:

**What database would you suggest for a startup that might possibly grow very fast?**

To be more specific:

 - We are using JSON to interchange data with mobile clients, so the data should be stored ideally in this format
 - The data model is relatively simple, like users, categories, history of
   actions... 
 - The users interact in "real time" (5 second propagation delay is still OK)
 - The queries are known beforehand (can cache results or use mapreduce)
 - The system would have up to 10000 concurrent users (just guessing...)
 - Transactions are a plus but can live without them I think
 - Spatially enabled is a plus
 - The data replication between nodes should be easy to administer
 - Open source
 - Hosting services available (we'd like to outsource the sysadmin part)

We have now a functional private prototype with a standard relational PostgreSQL/PostGIS. But scalability apart questions, I have to convert relational data to JSON and vice versa which seems like an overhead in high load.

I did a little research but I lack experience with all the new NoSQL stuff. <br/>
So far, I think of these solutions: 

 - Couchbase: master-master replication, native JSON document store, spatial extension, couchapps and although I don't know iriscouch hosting they seem good techs.<br/>
The downside I see so far is javascript debugging, disk occupation. 
 - MongoDb: has only one master but safe failover. Uses binary JSON.
 - Cluster MySQL: the evergreen of web (one master I think)
 - PostgresSQL&Slony: because I just love Postgres:-)

But there are plenty of others, Cassandra, Membase...
Do you guys have some real life experience? The bad one counts too! <br/>
Thanks in advance, 

Karel
scalable persistence for startup
===

this is my fist post on SO, so far I've been just lurking around... GREAT site!!<br/>
So here is my question:

**What database would you suggest for a startup that might possibly grow very fast?**

To be more specific:

 - We are using JSON to interchange data with mobile clients, so the data should be stored ideally in this format
 - The data model is relatively simple, like users, categories, history of
   actions... 
 - The users interact in "real time" (5 second propagation delay is still OK)
 - The queries are known beforehand (can cache results or use mapreduce)
 - The system would have up to 10000 concurrent users (just guessing...)
 - Transactions are a plus but can live without them I think
 - Spatially enabled is a plus
 - The data replication between nodes should be easy to administer
 - Open source
 - Hosting services available (we'd like to outsource the sysadmin part)

We have now a functional private prototype with a standard relational PostgreSQL/PostGIS. But scalability apart questions, I have to convert relational data to JSON and vice versa which seems like an overhead in high load.

I did a little research but I lack experience with all the new NoSQL stuff. <br/>
So far, I think of these solutions: 

 - Couchbase: master-master replication, native JSON document store, spatial extension, couchapps and although I don't know iriscouch hosting they seem good techs.<br/>
The downside I see so far is javascript debugging, disk occupation. 
 - MongoDb: has only one master but safe failover. Uses binary JSON.
 - Cluster MySQL: the evergreen of web (one master I think)
 - PostgresSQL&Slony: because I just love Postgres:-)

But there are plenty of others, Cassandra, Membase...
Do you guys have some real life experience? The bad one counts too! <br/>
Thanks in advance, 

Karel