Query Execution Optimization in Spark SQL

Algorithm 2

Calculation of the tuple number of join operation by histogram method.

	Estimate the size of join operation by histogram method
	input: HR = {h1r, h2r, …, hnr}, HS = {h1s, h2s, …, hms}
	Output: Total tuples Sum after join;
	procedure
	i ⟵ 1; j ⟵ 1; Sum ⟵ 0;
	while i ≤ n and j ≤ m do;
	if hi and hj have overlap then;
	Overlap ⟵ Overlap of two histogram buckets;
	templeft ⟵ hi.times ∗ Overlap/(hi.end-hi.start)
	tempright ⟵ hj.times ∗ Overlap/(hj.end-hj.start)
	Sum ⟵ Sum + templeft ∗ tempright/Overlap
	if hi.end < hj.end then
	i ⟵ i + 1
	else
	j ⟵ j + 1
	end if
	else
	if hi.end < hj.start then
	i ⟵ i + 1
	else
	j ⟵ j + 1
	end if
	end if
	end while
	end procedure