Question

Just reading through the search api documentation and have come across a stack overflow question with an answer that mentions a default “per-document consistent” indexes (Appengine Search API – Globally Consistent).

I can’t find any mention of this term in the App Engine documentation for the Search API and was wondering what this meant (or point me in the right direction).

Answer 1

Globally consistent indexes were deprecated in Version 1.7.3 (See: https://code.google.com/p/googleappengine/wiki/SdkReleaseNotes#Version_1.7.3_-_October_23,_2012)

The difference between consistency modes is explained in the source here: https://code.google.com/p/googleappengine/source/browse/trunk/python/google/appengine/api/search/search.py?r=281#2334

Specifically:

Consistency modes supported by indexes. When creating an index you
may request whether the index is GLOBALLY_CONSISTENT or
PER_DOCUMENT_CONSISTENT. An index with GLOBALLY_CONSISTENT mode set, when
searched, returns results with all changes prior to the search request,
committted. For an index with PER_DOCUMENT_CONSISTENT mode set, a search
result may contain some out of date documents. However, any two changes
to any document stored in such an index are applied in the correct order.
The benefit of PER_DOCUMENT_CONSISTENT is that it provides much higher
index document throughput than a globally consistent one.

Typically, you would use GLOBALLY_CONSISTENT if organizing personal
user information, to reflect all changes known to the user in any
search results. PER_DOCUMENT_CONSISTENT should be used in indexes
that amalgamate information from multiple sources, where no single
user is aware of all collected data.