New answers tagged storage
2
I am not entirely sure how much this information helps, but the system table pg_stats contains a correlation column.
From the manual
Statistical correlation between physical row ordering and logical ordering of the column values. This ranges from -1 to +1. When the value is near -1 or +1, an index scan on the column will be estimated to be cheaper ...
2
Sql server's query optimizer does not take variations in disk performance into consideration when compiling a query plan. Paul White provides a great overview of Sql Server's cost based optimizer here: http://sqlblog.com/blogs/paul_white/archive/2010/09/01/inside-the-optimizer-plan-costing.aspx
Some key points are:
The optimizer isn't trying to ...
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