To optimize performance,
the SQL procedure might use a hash join when an index join is eliminated
as a possibility. With a hash join, the smaller table is reconfigured
in memory as a hash table. PROC SQL sequentially scans the larger
table, and performs a row-by-row hash lookup against the small table
to form the result set. A memory-sizing formula determines whether
a hash join is used. The formula is based on the PROC SQL BUFFERSIZE
option, whose default value is 64 KB. On a memory-rich system, you
should consider increasing BUFFERSIZE to increase the likelihood that
a hash join is used.