Re: HASH_BLOBS hazards (was Re: PATCH: logical_work_mem and logical streaming of large in-progress transactions)

On Mon, Dec 14, 2020 at 01:59:03PM -0500, Tom Lane wrote:
> * Should we just have a blanket insistence that all callers supply
> HASH_ELEM?  The default sizes that dynahash.c uses without that are
> undocumented and basically useless.

+1

> we should just rip out all those memsets as pointless, since there's
> basically no case where you'd use the memset to fill a field that
> you meant to pass as zero.  The fact that hash_create() doesn't
> read fields it's not told to by a flag means we should not need
> the memsets to avoid uninitialized-memory reads.

On Mon, Dec 14, 2020 at 06:55:20PM -0500, Tom Lane wrote:
> Here's a rolled-up patch that does some further documentation work
> and gets rid of the unnecessary memset's as well.

+1 on removing the memset() calls.  That said, it's not a big deal if more
creep in over time; it doesn't qualify as a project policy violation.

> @@ -329,6 +328,11 @@ InitShmemIndex(void)
>   * whose maximum size is certain, this should be equal to max_size; that
>   * ensures that no run-time out-of-shared-memory failures can occur.
>   *
> + * *infoP and hash_flags should specify at least the entry sizes and key

s/should/must/