Description

Sometimes it'd be much more efficient to "fuse" a function into the loading of a field rather than load the whole field and apply the function. Take, for example, MV_MIN:

FROM foo | EVAL f = MV_MIN(f) | STATS SUM(f)

This'd be faster because:

1. Numeric doc values are stored in sorted order. Instead of loading them all we could just get the first one.
2. Instead of making a Block and then running the MV_MIN implementation to turn it into a Vector, we could save the block allocations entirely.

There are likely a bunch of cases that could benefit slightly from this, but things like SUBSTRING and MV_MIN and MV_MAX feel like they'd get the most benefit right now because they'd save on allocations.

But the real killer use case is for when we implement geo_shape style points, specifically, we'll end up with a function to simplify the geometry

CC @iverase and @craigtaverner and @costin

• Push vector similarity functions using BlockDocValuesReader #137002
• ESQL: Make field fusion generic #137382
• ES|QL - vector similarity pushdown follow up #137564
• ESQL: Leftovers from making field pushing generic #137679