noSQL 2+2 categories: more notes

Q: is Sandra a document DB? Hierarchical for sure. I think it could be a graph DB with a hierarchical interface
Q: which category most resembles RDBMS? DocStore compares 2 columnar vs a DocStore product and shows “not good for“!

–category: graph DB? lest used, most specialized. Not worth learning
–category: columnar DB? less used in the finance projects I know.
eg: Cassandra/HBase, all based on Google BigTable

Not good at data query across rows.

–category: document store, like Mongo

  • hierarchy — JSON and XML
  • query into a document is supported (In contrast, key-value store is opaque.) Index into a document?
  • index is absolutely needed to avoid full table scan
  • search by a common attribute
  • hierarchical document often contains maps or lists in an enterprise application. I think it’s semi-structured. More flexible than a RDBMS schema

–category: distributed hashmap, like redis/memcached

  • usage — pub/sub
  • Key must support hashing. Value can be anything
  • Value can be a hierarchical document !
  • Opaque — What if your value objects have fields? To select all value objects having a certain field value, we may need to use the field value as key. Otherwise, full table scan is inevitable. I think document store supports query on a field in a document. However, I think Gemfire and friends do support query into those fields.

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