opt: validate logical properties during execution tests

[justinj]

The logical properties of a relational expression are basically statements of facts about that expression - it would be valuable for us to validate that those statements are accurate. One way to do this might be to add an extra operator on top of every operator that just passes through its rows and also errors of one of the various logical properties are violated.

Jira issue: CRDB-4850

[andy-kimball]

@justinj, how does this differ from what we do today in checkExpr (which we run on -race builds)?

[justinj]

@andy-kimball this would actually occur during execution, rather than planning, and would verify that the assertions made by logical props are actually true in practice. I recall @RaduBerinde and I both independently tried some of this and didn't find anything, though

[RaduBerinde]

What I tried is in this branch: RaduBerinde@8cba3bb
It's a planNode that checks not-null columns and cardinality (with a planNode). We wrap every node int he plan with one of these. Didn't find anything in the logictests or bigtesst. Next step would be to validate FDs (at least on a sampling of the rows).

[RaduBerinde]

This would be very valuable to test FDs. We could set up tests like this:

• come up with a bunch of test table schemas
• for each table, fill up the table in the following way: generate all possible combinations for all the columns with values from a small set, e.g. (NULL, 1, 2, 3). Randomize the rows and insert them one by one, ignoring errors.
• run various queries on the table (e.g. with random filters) with the assertions enabled

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