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https://issues.apache.org/jira/browse/COUCHDB-623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12799864#action_12799864
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Chris Anderson commented on COUCHDB-623:
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It's worth nothing that another advantage to using the storage btrees is the
MVCC guarantees. This means that a slow client can take its sweet time to
traverse the view index, and is not affected by ongoing writes or deletes.
This is crucial for the consistency guarantees views make.
It is not very hard to create alternate view index systems (like
CouchDB-Lounge) and the overhead of running as an external is negligible. One
fine way to prototype a view system that optimizes for different things would
be as an external.
> File format for views is space and time inefficient - use a better one
> ----------------------------------------------------------------------
>
> Key: COUCHDB-623
> URL: https://issues.apache.org/jira/browse/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 forgotten.
> 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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