NonStop SQL/MP Reference Manual

NonStop SQL/MP Reference Manual—142115
E-19
Considerations—EXPLAIN
Expected rowcount For an operation other than a sort, shows the number of rows the
optimizer expects to be returned. For a join query, the rowcount is
cumulative for each join operation.
Appears for sort operations only if the purpose of the sort is to group
rows for a GROUP BY clause. In this case, shows the number of
rows expected after the GROUP BY operation finishes.
Hash cost Indicates the relative cost of the hash operation. Lower numbers
indicate more efficient and less costly execution.
Hash key columns Lists hash key columns ordered by selectivity, with the most selective
column first.
Hash rows in the Specifies whether the rows hashed are from the scan from the
previous operation (current table) or from a composite table.
Index pred. Shows the predicates evaluated on the index and indicates whether
evaluation is performed by the file system or the disk process.
Index selectivity Shows the percentage of the index that is scanned for the operation.
Join strategy Shows the type of join used: nested, (sort) merge, key-sequenced
merge, hash, or hybrid hash. For parallel or repartitioned hash joins,
additional lines list the partitions accessed by the ESPs and the CPUs
for the ESPs.
Lock mode Indicates whether locks are exclusive, shared, or the default. With the
default in effect, the system determines the actual lock mode used.
MDAM predicate
set
Indicates the predicate set used for the first step in the query.
next set Indicates the predicate set used for a subsequent step in the query.
Operation n Indicates the type of operation and the order of the operation in the
overall plan.
Operation cost Indicates the relative cost of performing the operation. Lower
numbers indicate more efficient and less costly operation.