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.
