count memory cost for returned []byte or SliceLocation

[lance6716]

Enhancement

We have limited the total memory block acquired from membuf.Pool to 16G, but the keys and values type which has their underlying array pointing to membuf.Pool also costs a lot memory so the node may OOM.

⬇️

[tangenta]

Adding index with global sort encounter OOM. We need to merge the fix to release-7.6. Let me change this issue to bug.