indexing - What is generic name of this technique CouchDB uses to index aggregated data -

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couchdb employs a cool pattern can used in multitude of other scenarios. i'm talking persisted b-tree index of map/reduce results. idea precalculate aggregated data , store @ different levels of b-tree index. index can used efficiently query aggregate without having reaggregate data time. then, if leaf-level value changes, ascending path through tree has recalculated.

for example, if data price on time, index store sum , count of items @ day, month, , year levels. then, if wants query average price year-to-date had sum sums , counts full months since year start, plus days available last month, divide total sum total count. if past price has change, change has propagate through index, corresponding day's , month's , year's values have updated, , values other days , other months within year can reused calculation.

what generic name of approach? similar exists in of popular rdbmses? experience using in practice?

materialized view

"a materialized view database object contains results of query. local copies of data located remotely, or used create summary tables based on aggregations of table's data. materialized views, store data based on remote tables, known snapshots."

this wikipedia article discusses storing of results in context of rdbms.

personally prefer term "indexed view". found wikipedia article searching "indexed view" on google.


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