Commits on May 7, 2024

1. opt: don't apply huge cost for full scans of virtual tables …

   This commit fixes - what I believe is - an oversight where we applied
   the huge cost to the plans with full scans of virtual tables when
   `disallow_full_table_scans` variable is set. The intent behind this
   penalty is to make plans with full scans prohibitively expensive so
   that other plans (without full scans) would be preferred, and if
   there is no other plan, then the query would error out. Implementation
   of this approach was incomplete for virtual tables: namely, we'd apply
   the cost penalty, but then we would not actually error out the query.
   Additionally, given that we don't have stats on virtual tables, we
   would apply the cost penalty to all full scans of virtual tables.
   
   As a result, we would either pick a plan without the full scan (that
   might actually be worse) or would allow the plan with the full scan to
   get executed still. We would also favor plans with fewer full scans of
   virtual tables (which might also be worse than had we not applied the
   cost penalty). This commit adjusts the code to not apply the cost
   penalty to full scans of virtual tables.
   
   This change is gated based on the new session variable
   `optimizer_apply_full_scan_penalty_to_virtual_tables` which defaults to
   `false` on master. We can discuss on the backport PRs whether it should
   be default to `true` there to require users to opt in for this PR to
   have an effect.
   
   Release note: None

   

   yuzefovich committed May 7, 2024
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