[COUCHDB-1027] More efficient implementation of the DB updater BTree functions

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.1, 1.2, 2.0.0
• Component/s: Database Core
• Assignee: Filipe David Borba Manana
• Reporter: Filipe David Borba Manana
• Created: 17/Jan/11 11:26
• Updated: 17/Jan/11 20:37
• Resolved: 17/Jan/11 11:50

Description

Currently, some of the BTree functions (by_id BTree reduce function and and by_seq BTree split function) traverse the same input lists several times to produce the output. This is not optimal. For example, the btree_by_id_reduce function, for a database with 300 000+ documents, can easily get a list of 50 or more #full_doc_info records. This functions traverses that list 4 times - 2 filtered list comprehensions plus two length/1 calls.

The following patch changes the implementation to produce the same output with a single list traversal operation.