•memory — Memory

•memory x gives a record of what this thread holds, and of what x keeps alive. •memory 0 is the usual spelling for the counts alone.

• records counts the live record nodes: the linear calls that reverse mode records while ∂ runs. Each ∂ frees its record when it returns, so the count is 0 between programs.
• pending counts the live pending arrays, whose items wait for their first read.
• bytes counts the bytes that x keeps alive: its items, the base of a view, the arrays that a pending array reads, the parts of a value that ∂ is differentiating, and the nodes of a record. An allocation that x reaches twice counts once.

records and pending count the nodes that this thread made, even when another thread holds one. •memory reads no items, so it never forces a pending array, and it accepts values that ∂ is differentiating.

{+/⍵×⍵}∂ 1 2 3     ⍝ 2 4 6
•memory 0          ⍝ ["records":0ₓ "pending":0ₓ "bytes":0ₓ]

A reshape is a view, which keeps all of its base’s items alive:

v←⍳1000ₓ
m←2 500⍴v
(•memory m).bytes  ⍝ 2000ₓ

•explain reports what happened while an expression ran.