Question Set C - Due this Sunday

All Questions sets should be answered in a single plain textfile that is nicely formatted for reading.

Why are dynamic user populations a driver for nosql databases today?
NoSQL is flexable where current RDBMS are disruptive to reshard and impact applications. Also, it difficult for RDBMS to make cross-sharding joins. In another instances of RDBMS the schema managment can be very diffucilt.  NoSQL provide no schema required before inserting data, no schema change required to change data formats, auto-sharding without application participation, can handle distributed queries.

Why is scaling of 3-tier architectures important for nosql databases today?
Having the seperation of tiers is still an architectural imporance.  

How is Membase different than Memcached?
Memcached - in-memory only no file backup; limited set of operations; not aware of value stored-cannot query on value; mostly a get request; no replication; when adding noded to a cluster there could be a point where data is not fully avaiable (consitent hasing) Membase - Is a file based with buit-in memcached cache interface which will re-populate on restart on system fail; added replication, add capacity to cluster in a non-disrtiptive way by auto move data to ensue theres not a preriod where data is not avalible; added replicaiton if node dies other copyies data is abalve.- membased info is gone and could slowdown productiviedy.

How is Couchdb different than Couchbase?
The major difference between Couchdb and Couchbase is Couchdb does not have Membase frontend like Couchbase.  Also, Couchbase contains auto-sharding cluster technology, Live cluster reconfiguration, Memcached-compatilbe API.

How does eventual consistency work for web apps? Be sure and give specific examples.
Eventual consistency in webapps - if a distrubutive database is presenet then the given database must tolerate a partition and brakage in condutivity betweens nodes. There are two relative outcomes for facliliting the database operations, one continue to have the the datbase fully avaialble for writing of any key/vale pair or favor consisitency were part of the database is not avaialbele and continue to write key/value pairs allow conflicts.

What are the advantages and disadvantages of the document-style nosql databases?
Some advangates are performace, it allows consisently, low latency access to data. Dynamic elastic, able to move data from one server to another. Schema flexibility were no DBA is need to change the database schema to add or remove elements.  Finally, Query flexiblity.

What is MVCC? How does it work in couchdb?
MVCC is Multi-Version Concurrency Control (MVCC) which mamages concurent access to a database.  This is important with a user requests a document and at the sametime a second user is changing the same document. The second user created an entirly new version of the given document. Couchdb will point to the new version that has just been written.