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From Apache Wiki <>
Subject [Couchdb Wiki] Update of "Introduction to CouchDB views" by PaulDavis
Date Sun, 12 Apr 2009 17:15:55 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Couchdb Wiki" for change notification.

The following page has been changed by PaulDavis:

  For more details see [ this blog post]
- In addition: reduce functions should not grow its output larger than log(n) where n is the
number of input rows. ''(Reference needed)''
+ === Reduced Value Sizes ===
+ As CouchDB computes view indexes it also calculates the corresponding reduce values and
caches this value inside each of the btree node pointers. This scheme allows CouchDB to reuse
reduced values when updating the btree. This scheme requires some care to be taken with the
amount of data returned from reduce functions.
+ As a rule of thumb, the data returned by reduce functions should remain "smallish" and not
grow faster than log(num_rows_processed). Although violating this requirement will not cause
an error, btree performance will degrade drastically. If you have a view that appears to work
well on small data sets but grinds to a halt as more data is added you're probably violating
the growth rate characteristics.
  == Interactive CouchDB Tutorial ==

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