Algorithms
summary
A Sinatra app catalogs a record collection and builds pie charts for the frequency of every value across columns. The first implementation is a mapreduce-like threaded scan that takes about 23.5 seconds for 9,000 items; caching helps but doesn't scale. Replacing the Ruby aggregation with a single SQL GROUP BY query on Postgres drops the same job to ~0.5 seconds, showing use SQL for heavy counting and grouping rather than pulling everything into Ruby.
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