In 8.0, the query team is introducing a fast path for query optimization and execution called the "express" path. The express path is an optimization for a limited set of queries that can use simple index scan or clustered index scan plans. For example, many "IDHACK"-eligible queries (point lookups on the _id index) will now use the express path instead.

In explain output and slow query logs, these new kinds of query plans will show up as "EXPRESS_IXSCAN" and "EXPRESS_CLUSTERED_IXSCAN" instead of "IXSCAN", "CLUSTERED_IXSCAN" and "IDHACK".

For example, the winningPlan for express plans will look similar to:

winningPlan: {
    stage: "EXPRESS_IXSCAN",
    keyPattern: { _id: 1 },  // example 
    indexName: "_id_",    // example
    ...
}

Description of Linked Ticket

Right now the planSummary simply says "EXPRESS", but it could be more like "EXPRESS {a: 1}"