Index pruning can prune useful indexes when OR pushdown occurs

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    • Type: New Feature
    • Resolution: Unresolved
    • Priority: Major - P3
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    • Affects Version/s: None
    • Component/s: None
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    • Query Optimization
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      In SERVER-94738 (from HELP-64477) we saw that index pruning logic did not account for OR pushdowns, and would prune indexes that could potentially create stricter bounds using the pushed down predicates:

      assert.commandWorked(coll.createIndex({a: 1, unused_field: 1}))
assert.commandWorked(coll.createIndex({a: 1, b: 1}))
coll.find({ $or: [{a: 1}, {a: {$exists: false}}], b: 2 }).explain()
// with index pruning enabled, this query would not consider the {a: 1, b: 1} index

      We should have index pruning either bail out in these cases, or account for the OR pushdown. Here is bailout logic that fixes this issue.

      As part of this ticket, we should also expand testing of different AND/OR cases, to make sure we don't prune useful indexes in other scenarios. SERVER-92232 will also help in this scenario.

            Assignee:
            Unassigned
            Reporter:
            Chris Harris
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              Created:
              Updated: