The
SPD Server WHERE clause planner does the tuning work for you by automatically costing the different approaches to
index evaluation. The SPD Server
WHERE clause planner avoids computation-intensive operations and uses simple computations where
possible.
WHERE clause EVAL strategies SPD Server indexing keeps track of the cardinality ratio
and distribution of variable values
in a table and uses them to calculate the cost of a WHERE clause. The WHERE clause
planner uses four evaluation strategies to determine the number of rows that will
be required
to execute a given query.
EVAL 6 emulates the behavior of EVAL 2. EVAL 6 means that the query is a candidate
for
Hadoop WHERE processing. If the Hadoop WHERE processing fails, EVAL 6 reverts to EVAL 2 operation. EVAL 6
takes true rows as determined by EVAL 1, EVAL 3, or EVAL 4, and then eliminates any
rows shown to be false, leaving a table that contains only true rows. EVAL 2 processes
all rows of a table when no index evaluation is possible. For example, no index evaluation
is possible when an index is not present or when some predecessor
function performs an operation that invalidates the index.