This change enables additional scenarios in the slot-based execution engine (SBE), the new query execution engine that the query execution team has been working on for the last few years. The SBE engine was enabled in a limited way in 6.0 but was first broadly enabled in 6.3 under SERVER-71798.

This change goes further and enables even more scenarios in SBE for the 7.0 LTS release. The change in execution engine should be largely transparent to applications and end-users. However, given the scope of the changes between Classic and SBE, performance differences are possible. (For the most part SBE in 7.0 is a faster engine when compared to the Classic Engine.)

The fact that SBE is being used under the hood will show up in the server's debug mechanisms, which is the main reason that I've marked this as needing downstream attention. In particular, the explain output will look substantially different for SBE. Explain output for queries using the classic engine report explainVersion:"1" whereas explain output for queries using SBE report explainVersion:"2".

There are also some differences in debug output produced by $planCacheStats as well as changes in system.profile and slow query log lines (e.g. an indication that SBE was the engine used).

Description of Linked Ticket

This is the same as SERVER-71798, but for 7.0.