Re: clarify equalTupleDescs()

On 07.02.24 04:06, jian he wrote:
> /*
>   * hashRowType
>   *
>   * If two tuple descriptors would be considered equal by equalRowTypes()
>   * then their hash value will be equal according to this function.
>   */
> uint32
> hashRowType(TupleDesc desc)
> {
> uint32 s;
> int i;
> 
> s = hash_combine(0, hash_uint32(desc->natts));
> s = hash_combine(s, hash_uint32(desc->tdtypeid));
> for (i = 0; i < desc->natts; ++i)
> s = hash_combine(s, hash_uint32(TupleDescAttr(desc, i)->atttypid));
> 
> return s;
> }
> 
> from the hashRowType comment, should we also hash attname and atttypmod?

In principle, hashRowType() could process all the fields that 
equalRowTypes() does.  But since it's only a hash function, it doesn't 
have to be perfect.  (This is also the case for the current 
hashTupleDesc().)  I'm not sure where the best tradeoff is.