[tor-bugs] #2923 [Metrics]: Improve materialized views in the metrics database

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#2923: Improve materialized views in the metrics database
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 Reporter:  karsten      |          Owner:  karsten
     Type:  enhancement  |         Status:  new    
 Priority:  normal       |      Milestone:         
Component:  Metrics      |        Version:         
 Keywords:               |         Parent:         
   Points:               |   Actualpoints:         
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 The [https://gitweb.torproject.org/metrics-
 web.git/blob/HEAD:/db/tordir.sql metrics database schema] uses
 periodically updated tables similar to materialized views for aggregating
 statistics.  When inserting data into the database, we write the dates
 that have changed to a separate updates table.  Every three hours, we
 delete the aggregates for these days and recompute them, which takes a few
 minutes.

 The recompute step that takes most of the time is `refresh_user_stats()`,
 which is no surprise given the complexity of that function.  We should try
 to simplify this function, possibly by pre-computing partial results that
 can be reused for other statistics.  Ideally, recomputing aggregates
 should run in under one minute, given that we want to add more
 materialized views for more aggregate statistics in the future.  In
 particular, I'd like to know which particular SQL parts slow us down in
 order to avoid them in the future.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/2923>
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