Query statistics section provides performance debugging information
If the EXPLAIN_STAT configuration parameter is enabled, a Query Statistics section appears in the explain output file that the SET EXPLAIN statement of SQL and the onmode -Y session_id command displays.
The Query Statistics section of the explain output file shows the estimated number of rows that the query plan expects to return, the actual number of returned rows, and other information about the query. You can use this information, which provides an indication of the overall flow of the query plan and how many rows flow through each stage of the query, to debug performance problems.
The following example shows query statistics in SET EXPLAIN output. If the estimated and actual number of rows scanned or joined are quite different, the statistics on those tables might be old and should be updated.
select * from tab1, tab2 where tab1.c1 = tab2.c1 and tab1.c3 between 0 and 15
Estimated Cost: 104
Estimated # of Rows Returned: 69
1) zelaine.tab2: SEQUENTIAL SCAN
2) zelaine.tab1: INDEX PATH
(1) Index Keys: c1 c3 (Serial, fragments: ALL)
Lower Index Filter: (zelaine.tab1.c1 = zelaine.tab2.c1
AND zelaine.tab1.c3 >= 0 )
Upper Index Filter: zelaine.tab1.c3 <= 15
NESTED LOOP JOIN
Query statistics:
-----------------
Table map :
----------------------------
Internal name Table name
----------------------------
t1 tab2
t2 tab1
type table rows_prod est_rows rows_scan time est_cost
-------------------------------------------------------------------
scan t1 50 50 50 00:00:00 4
type table rows_prod est_rows rows_scan time est_cost
-------------------------------------------------------------------
scan t2 67 69 4 00:00:00 2
type rows_prod est_rows time est_cost
-------------------------------------------------
nljoin 67 70 00:00:00 104