Approximate by construction — it counts the backing buffers a packed
column owns, which is what a cache budget is actually trying to bound,
and ignores per-object overhead. A chunked column reports the sum of
its chunks. A column whose kind this cannot size returns 0 rather
than guessing, so a budget treats it as free instead of evicting on a
fabricated number.
Bytes rather than entries is the point: a 500k-row result and a scalar
both count as one entry, and only one of them matters.
Retained size of a column value, in bytes.
Approximate by construction — it counts the backing buffers a packed column owns, which is what a cache budget is actually trying to bound, and ignores per-object overhead. A chunked column reports the sum of its chunks. A column whose kind this cannot size returns
0rather than guessing, so a budget treats it as free instead of evicting on a fabricated number.Bytes rather than entries is the point: a 500k-row result and a scalar both count as one entry, and only one of them matters.