Block nested loop

A block-nested loop (BNL) is an algorithm used to join two relations in a relational database.

This algorithm is a variation of the simple nested loop join and joins two relations |R|<|S|. In a traditional nested loop join, R tuples, and particularly if there is no applicable index for the join key on R tuples. Here groups are disjoint sets of tuples in R tuples into memory and loads them into a hash table. It then scans R. This reduces the number of scans of S. This further reduces the number of scans of O(PrPs/M) I/Os where Ps is size of O(Pr+Ps) I/Os if "Block Nested Loop Join". MariaDB. MariaDB Corporation Ab. Retrieved 2 August 2015.