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From "Roger Binns (JIRA)" <>
Subject [jira] Created: (COUCHDB-623) File format for views is space and time inefficient - use a better one
Date Wed, 13 Jan 2010 18:20:54 GMT
File format for views is space and time inefficient - use a better one

                 Key: COUCHDB-623
             Project: CouchDB
          Issue Type: Improvement
          Components: Database Core
    Affects Versions: 0.10
            Reporter: Roger Binns

This was discussed on the dev mailing list over the last few days and noted here so it isn't

The main database file format is optimised for data integrity - not losing or mangling documents
- and rightly so.

That same append-only format is also used for views where it is a poor fit.  The more random
the ordering of data supplied, the larger the btree.  The larger the keys (in bytes) the larger
the btree.  As an example my 2GB of raw JSON data turns into a 3.9GB CouchDB database but
a 27GB view file (before compacting to 900MB).  Since views are not replicated, this requires
a disproportionate amount of disk space on each receiving server (not to mention I/O load).
 The format also affects view generation performance.  By loading my documents into CouchDB
in an order by the most emitted value in views I was able to reduce load time from 75 minutes
to 40 minutes with the view file size being 15GB instead of 27GB, but still very distant from
the 900MB post compaction.

Views are a performance enhancement.  They save you from having to visit every document when
doing some queries.  The data within in a view is generated and hence the only consequence
of losing view data is a performance one and the view can be regenerated anyway.  Consequently
the file format should be one that is optimised for performance and size.  The only integrity
feature needed is the ability to tell that the view is potentially corrupt (eg the power failed
while it was being generated/updated).

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