Talk for pre-Fosdem MySQL Day on February 1, 2019.
Last year I worked on several tickets where data follow the same pattern: millions of popular products fit into a couple of categories and rest used the rest. We had a hard time to find a solution for retrieving goods fast.
MySQL 8.0 has a feature which resolves such issues: optimizer histograms, storing statistics of an exact number of values in each data bucket.
However in real life histograms help not with all queries, accessing non-uniform data. How you write a query, the number of rows in the table, data distribution: all these may affect the use of histograms.
In this session I show examples, demonstrating how Optimizer uses histograms.