10 minutes after I did a webinar, explaining how we need to be specific about database storage and never use the unbelievably unhelpful and pointless term "NoSQL".
What I asked: What can you tell me about that type of database?
Response: It's a NoSQL database.
What I meant: What kind of structure does this database use? Relational? Hierarchical? Document? Graph? Key-value? Column-storage? Wide table? What kind of internal storage does this database use? B-tree? BW-tree? Memory mapping? Hash tables with linked lists? Is the data per collection/table or is that an abstraction for underlying partitions? Does the data format lend itself to easy horizontal partitioning (e.g. sharding)? If it's a sharded system, how does it deal with the scatter-gather problem and multi-node write confirmations? Is there a data router? Are replicas readable? Are there capabilities for edge nodes? How is data actually tracked (e.g. bitmaps, statistics)? Are records/documents mutable or immutable with delta structures? Are records deleted immediately or internally marked for deletion? What are this system's memory management strategy? What kind of aggregations are possible with this database? Are there silly 100MB aggregation limits or is it willing to use actually use the 128GB of RAM we just paid for specifically for the purpose of preventing our massive aggregates from needing to write to disk? Is there a transaction / an operations log? Is there support for transactions? How does this relate to rollbacks and commits? Are there various data isolation levels? Is locking pessimistic, optimistic, or just configurable? What can you tell me about available local partitioning strategies? Can you partition indexes to various local disks to optimize performance? What mechanisms allow us to optimize reads and writes separately? Is there native encryption at the database, table, field, or column level? Are there variable storage engines for this database? At what various levels does compression take place?
What I was told: You don't access it with SQL.