How We Built a Cost-Based SQL Optimizer

Re:How We Built a Cost-Based SQL Optimizer by radub on Thursday November 08, 2018 @03:45PM (#18409831)

[Cockroach Labs engineer here, I worked on statistics]

All table statistics are stored in a system table (system.table_statistics). CREATE STATISTICS scans the table, calculating statistics on a column, and adds a new row to system.table_statistics.

We still have a ways to go in making statistics automatic (right now it requires a manual call to CREATE STATISTICS) and more useful to the optimizer (which currently only uses basic stats). We're working on that right now for the 2.2 release.

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Re:How We Built a Cost-Based SQL Optimizer by SaifAlHarthi on Friday November 09, 2018 @01:16PM (#18416525)

What if the tables were partitioned, do you calculate local statistics or you aggregate the stats and expose it to the optimizer?

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Re:How We Built a Cost-Based SQL Optimizer by Lemaxoxo on Thursday November 08, 2018 @04:23PM (#18410183)

Are you planning to support multivariate statistics?

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Re:How We Built a Cost-Based SQL Optimizer by radub on Thursday November 08, 2018 @04:40PM (#18410299)

We plan to support cardinality estimations for multiple columns. Other than that there are no plans for multivariate stats in the near future.

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