google app engine - At what rate do indexes "explode" in GAE's big table? -


at rate indexes "explode" in gae's big table?

the excerpt documentation below explains collection values, indexes can "explode" exponentially.

does mean object 2 collection values, there index entry each subset of values in first collection paired each subset in second collection? or there index entry each possible pair of values?

example:

entity:

widget:{      mamas_list:         ['cookies', 'puppies']      papas_list:         ['rain', 'sun']     }

index entry each subset of values in first collection paired each subset in second collection:

cookies         rain cookies puppies rain cookies puppies rain sun cookies         sun cookies         rain sun puppies         rain puppies         sun puppies         rain sun

only index entry each possible pair of values:

cookies         rain cookies         sun puppies         rain puppies         sun

exploding indexes excerpt:

source: https://developers.google.com/appengine/docs/python/datastore/indexes#index_limits

an entity can have multiple values same property requires separate index entry each value; again, if number of possible values large, such entity can exceed entry limit.

the situation becomes worse in case of entities multiple properties, each of can take on multiple values. accommodate such entity, index must include entry every possible combination of property values. custom indexes refer multiple properties, each multiple values, can "explode" combinatorially, requiring large numbers of entries entity relatively small number of possible property values. (taken from: )

chris,

you'll have 'exploding index problem' in cases explicitly add index.yaml entry multiple repeated properties, , when objects saved table have many multiple properties.

in example, index.yaml add index?

- kind: widget   properties:   - name: mamas_list   - name: papas_list

if save sample object datastore:

widget(mamas_list=['a', 'b'], papas_list['c', 'd']).put()

there 4 different indexes saved:

['a', 'c'] ['a', 'd'] ['b', 'c'] ['b', 'd']

the whole purpose of adding index allow querying these 2 properties:

widget.query().filter(mamas_list=='a').filter(papas_list=='d').fetch()

you avoid exploding index (not found in sample case), using zig-zag algorithm indexes:

http://www.google.com/events/io/2010/sessions/next-gen-queries-appengine.html


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