Julian Hyde created OPTIQ-429:
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Summary: Add statistics SPI for lattice optimization algorithm
Key: OPTIQ-429
URL: https://issues.apache.org/jira/browse/OPTIQ-429
Project: Optiq
Issue Type: New Feature
Reporter: Julian Hyde
Assignee: Julian Hyde
In OPTIQ-427 we added an an optimization algorithm to choose an initial set of
tiles to materialize. The {{rowCountEstimate}} attribute is the number of rows
in the lattice.
Add an SPI to generate estimates of (a) the number of rows in the lattice, (b)
the number of rows in a given tile of the lattice (specified by its dimensions).
Also add a default implementation of the SPI that executes SQL queries, caches
the results, and uses some kind of approximation for the cardinalities of sets
of attributes e.g. if quarter has 4 distinct values and year has 10 distinct
values then (year, quarter) has 40 distinct values (or perhaps an expectation
of 39.79 distinct values in a table with 3,650 rows, per the formula {{n . (1 -
((n - 1) / n) ^ p)}}).
Implementations that read stats from external stats tables, or execute SQL that
samples a small percentage of the rows, would also be possible.
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