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The hash join is an example of a join algorithm and is used in the implementation of a relational database management system.All variants of hash join algorithms involve building hash tables from the tuples of one or both of the joined relations, and subsequently probing those tables so that only tuples with the same hash code need to be compared for equality in equijoins.
(Nested loops occur when one loop is inside of another loop.) One classical usage is to reduce memory access latency or the cache bandwidth necessary due to cache reuse for some common linear algebra algorithms. The technique used to produce this optimization is called loop tiling, [1] also known as loop blocking [2] or strip mine and interchange.
It then scans , and probes the hash table to find tuples that match any of the tuples in the current page of . This reduces the number of scans of S {\displaystyle S} that are necessary. algorithm block_nested_loop_join is for each page pr in R do for each page ps in S do for each tuple r in pr do for each tuple s in ps do if r and s satisfy ...
Block nested loop; H. Hash join; N. Nested loop join; S. Sort-merge join; Symmetric hash join; W. Worst-case optimal join algorithm This page was last edited on 22 ...
algorithm nested_loop_join is for each tuple r in R do for each tuple s in S do if r and s satisfy the join condition then yield tuple <r,s> This algorithm will involve n r *b s + b r block transfers and n r +b r seeks, where b r and b s are number of blocks in relations R and S respectively, and n r is the number of tuples in relation R.
Loop-invariant code motion – this can vastly improve efficiency by moving a computation from inside the loop to outside of it, computing a value just once before the loop begins, if the resultant quantity of the calculation will be the same for every loop iteration (i.e., a loop-invariant quantity). This is particularly important with address ...
The effectiveness of loop interchange depends on and must be considered in light of the cache model used by the underlying hardware and the array model used by the compiler. In C programming language , array elements in the same row are stored consecutively in memory (a[1,1], a[1,2], a[1,3]) ‒ in row-major order .
Integer programming is NP-complete, and Maydan showed that the problem of checking array aliasing in nested loops with affine bounds and subscripts is equivalent to integer programming; other operations, such as array dataflow analysis, are even more complex (the algorithms of the Omega Library handle the full language of Presburger Arithmetic ...