Re: Optimizing ResouceOwner to speed up COPY

On 17/10/2025 06:13, Chao Li wrote:
> ```
> @@ -250,12 +257,21 @@ ResourceOwnerAddToHash(ResourceOwner owner, Datum value, const ResourceOwnerDesc
> idx = hash_resource_elem(value, kind) & mask;
> for (;;)
> {
> + /* found an exact match - just increment the counter */
> + if ((owner->hash[idx].kind == kind) &&
> + (owner->hash[idx].item == value))
> + {
> + owner->hash[idx].count += count;
> + return;
> + }
> +
> if (owner->hash[idx].kind == NULL)
> break; /* found a free slot */
> idx = (idx + 1) & mask;
> }
> ```
>
> I think this is the “trade-off” you mention in your email: if a free slot found earlier, then still gets duplicated entries. I have no concern to this “trade-off”, but please add a comment here, otherwise future readers may be confused, and might potentially consider that were a bug, without reading your original design email.

+1 on such a comment. Here or maybe on the ResourceElem struct itself.

> typedef struct ResourceElem
> {
> Datum item;
> + uint32 count; /* number of occurrences */
> const ResourceOwnerDesc *kind; /* NULL indicates a free hash table slot */
> } ResourceElem;

Hmm, the 'count' is not used when the entry is stored in the array.
Perhaps we should have a separate struct for array and hash elements
now. Keeping the array small helps it to fit in CPU caches.

> /*
> * Forget that an object is owned by a ResourceOwner
> *
> * Note: If same resource ID is associated with the ResourceOwner more than
> * once, one instance is removed.
> *
> * Note: Forgetting a resource does not guarantee that there is room to
> * remember a new resource. One exception is when you forget the most
> * recently remembered resource; that does make room for a new remember call.
> * Some code callers rely on that exception.
> */
> void
> ResourceOwnerForget(ResourceOwner owner, Datum value, const ResourceOwnerDesc *kind)

Does this break the exception noted in the above comment? I guess it
still holds because we don't deduplicate entries in the array. That's
very subtle, needs a comment at least.

typo: ocurrence -> occurrence

- Heikki