FIRST_ROWS vs. ALL

From: Carle, William T (Bill), NLCIO <wcarle_at_att.com>
Date: Mon, 03 Dec 2001 11:35:28 -0800
Message-ID: <F001.003D3989.20011203112631@fatcity.com>

Howdy,

I have a query which was taking an extremely long time to complete. The OPTIMIZER_MODE in the init.ora file is set to CHOOSE, meaning it will use the ALL_ROWS method to determine its access paths. I determined the query was not using the indexes I thought it should. When I changed to use the FIRST_ROWS optimizer_mode, the query ran in under a second. Now FIRST_ROWS is used to minimize response time; ALL_ROWS is used to minimize total execution time. I'm trying to figure out the difference. Using FIRST_ROWS, this is the output from tkprof:

select ra.originatingclli, ra.terminatingclli, r.originatingclli, r.terminatingclli, r.deletedigits, r.prefixdigits, rs.originatingclli, rs.terminatingclli from routingassignmentpersistent ra, route r, routesegmentroute rs1, routesegmentpersistent rs where networktype
= 'A

C' and networksubtype
= 'POTS' and ra.objid = r.ROUTINGASSIGNPERSFINAL_OBJID and
r.objid = ROUTE_OBJID and ROUTESEGMENTPERSISTENT_OBJID = rs.objid and rownum < 5 and ra.startdate is not null

call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ----------

Parse 1 0.00 0.01 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 2 0.00 0.00 0 35 0 4
------- ------ -------- ---------- ---------- ---------- ----------

total 4 0.00 0.01 0 35 0 4

Misses in library cache during parse: 1
Optimizer goal: FIRST_ROWS
Parsing user id: 29 (NTOPBIG)

Rows Row Source Operation

-------  ---------------------------------------------------
      4  COUNT STOPKEY
      4   NESTED LOOPS
      4    NESTED LOOPS
      2     NESTED LOOPS
      1      TABLE ACCESS BY INDEX ROWID ROUTINGASSIGNMENTPERSISTENT
      1       INDEX RANGE SCAN (object id 16976)
      2      TABLE ACCESS BY INDEX ROWID ROUTE
      2       INDEX RANGE SCAN (object id 16962)
      5     TABLE ACCESS BY INDEX ROWID ROUTESEGMENTROUTE
      5      INDEX RANGE SCAN (object id 16971)
4       TABLE ACCESS BY INDEX ROWID ROUTESEGMENTPERSISTENT
                7     INDEX UNIQUE SCAN (object id 16965)


                Rows     Execution Plan
                -------  ---------------------------------------------------
                      0  SELECT STATEMENT   GOAL: FIRST_ROWS
                      4   COUNT (STOPKEY)
                      4    NESTED LOOPS
                      4     NESTED LOOPS
                      2      NESTED LOOPS
                      1       TABLE ACCESS   GOAL: ANALYZED (BY INDEX ROWID)
OF
                                  'ROUTINGASSIGNMENTPERSISTENT'
                      1        INDEX   GOAL: ANALYZED (RANGE SCAN) OF
                                   'IX_ROUTINGASSIGNMENTPERSIST5'
(NON-UNIQUE)
                      2       TABLE ACCESS   GOAL: ANALYZED (BY INDEX ROWID)
OF
                                  'ROUTE'
                      2        INDEX   GOAL: ANALYZED (RANGE SCAN) OF
'IX_ROUTE4'
                                   (NON-UNIQUE)
                      5      TABLE ACCESS   GOAL: ANALYZED (BY INDEX ROWID)
OF
                                 'ROUTESEGMENTROUTE'
                      5       INDEX   GOAL: ANALYZED (RANGE SCAN) OF
                                  'IX_ROUTESEGMENTROUTE3' (NON-UNIQUE)   
                      4     TABLE ACCESS   GOAL: ANALYZED (BY INDEX ROWID)
OF
                                'ROUTESEGMENTPERSISTENT'
                      7      INDEX   GOAL: ANALYZED (UNIQUE SCAN) OF
                                 'IX_ROUTESEGMENTPERSISTENT' (UNIQUE)

                Using the ALL_ROWS mode, this is the tkprof output from the

same query:

call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ----------

Parse 1 0.02 0.01 0 0 0 0
Execute 2 0.05 0.06 0 0 5 0
Fetch 2 40.91 471.49 197287 803265 3128 4
------- ------ -------- ---------- ---------- ---------- ----------

total 5 40.98 471.56 197287 803265 3133 4

Misses in library cache during parse: 1
Optimizer goal: ALL_ROWS
Parsing user id: 29 (NTOPBIG)

Rows Row Source Operation

-------  ---------------------------------------------------
      4  COUNT STOPKEY
      4   MERGE JOIN
      4    SORT JOIN
 344066     NESTED LOOPS
 166100      HASH JOIN
 102265       TABLE ACCESS BY INDEX ROWID ROUTINGASSIGNMENTPERSISTENT
 164524        INDEX RANGE SCAN (object id 16976)
 709657       TABLE ACCESS FULL ROUTE
 344066      TABLE ACCESS BY INDEX ROWID ROUTESEGMENTROUTE
 510165       INDEX RANGE SCAN (object id 16971)
      4    SORT JOIN
 155184     TABLE ACCESS FULL ROUTESEGMENTPERSISTENT

Rows     Execution Plan
-------  ---------------------------------------------------
      0  SELECT STATEMENT   GOAL: ALL_ROWS
      4   COUNT (STOPKEY)
      4    NESTED LOOPS
      4     NESTED LOOPS
 344066      HASH JOIN
 166100       TABLE ACCESS   GOAL: ANALYZED (FULL) OF
                  'ROUTINGASSIGNMENTPERSISTENT'
 102265       TABLE ACCESS   GOAL: ANALYZED (FULL) OF 'ROUTE'
 164524      TABLE ACCESS   GOAL: ANALYZED (BY INDEX ROWID) OF
                 'ROUTESEGMENTROUTE'
 709657       INDEX   GOAL: ANALYZED (RANGE SCAN) OF
                  'IX_ROUTESEGMENTROUTE3' (NON-UNIQUE)
 344066     TABLE ACCESS   GOAL: ANALYZED (BY INDEX ROWID) OF
                'ROUTESEGMENTPERSISTENT'
 510165      INDEX   GOAL: ANALYZED (UNIQUE SCAN) OF
                 'IX_ROUTESEGMENTPERSISTENT' (UNIQUE)

So how can the optimizer think that this second way can possibly be better? Whether you base it on total execution time, resource cost, or whatever?

Bill Carle
AT&T
Database Administrator
816-995-3922
wcarle_at_att.com

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-- 
Author: Carle, William T (Bill), NLCIO
  INET: wcarle_at_att.com

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Received on Mon Dec 03 2001 - 13:35:28 CST

FIRST_ROWS vs. ALL_ROWS