Is Couchbase an ordered key-value store?

Question

Are documents in Couchbase stored in key order? In other words, would they allow efficient queries for retrieving all documents with keys falling in a certain range? In particular I need to know if this is true for Couchbase lite.

Answer 1

Query efficiency is correlated with the construction of the views that are added to the server.

Couchbase/Couchbase Lite only stores the indexes specified and generated by the programmer in these views. As Couchbase rebalances it moves documents between nodes, so it seems impractical that key order could be guaranteed or consistent.

(Few databases/datastores guarantee document or row ordering on disk, as indexes provide this functionality more cheaply.)

Couchbase document retrieval is performed via map/reduce queries in views:

A view creates an index on the data according to the defined format and structure. The view consists of specific fields and information extracted from the objects in Couchbase. Views create indexes on your information that enables search and select operations on the data.

source: views intro

A view is created by iterating over every single document within the Couchbase bucket and outputting the specified information. The resulting index is stored for future use and updated with new data stored when the view is accessed. The process is incremental and therefore has a low ongoing impact on performance. Creating a new view on an existing large dataset may take a long time to build but updates to the data are quick.

source: Views Basics

source

and finally, the section on Translating SQL to map/reduce may be helpful:

In general, for each WHERE clause you need to include the corresponding field in the key of the generated view, and then use the key, keys or startkey / endkey combinations to indicate the data you want to select.

In conclusion, Couchbase views constantly update their indexes to ensure optimal query performance. Couchbase Lite is similar to query, however the server's mechanics differ slightly:

View indexes are updated on demand when queried. So after a document changes, the next query made to a view will cause that view's map function to be called on the doc's new contents, updating the view index. (But remember that you shouldn't write any code that makes assumptions about when map functions are called.)

How to improve your view indexing: The main thing you have control over is the performance of your map function, both how long it takes to run and how many objects it allocates. Try profiling your app while the view is indexing and see if a lot of time is spent in the map function; if so, optimize it. See if you can short-circuit the map function and give up early if the document isn't a type that will produce any rows. Also see if you could emit less data. (If you're emitting the entire document as a value, don't.)

from Couchbase Lite - View