To cache or materialize?

Question

Hi all,
I have a table with a few thousand rows of SDO_GEOMETRY (simple curves), and a view that returns the results of operations on them as follows:
CREATE TABLE BASE_GEOM
ID NUMBER,
CONTOUR MDSYS.SDO_GEOMETRY
/* ... populate this table with a bunch of closed curves ... */
CREATE OR REPLACE FORCE VIEW VW_DERIVED_VALS
AS
SELECT BG.ID,
SDO_GEOM.SDO_AREA (BG.CONTOUR, 0.005) AREA
FROM BASE_GEOM BG;
On a regular basis, I want to return the AREA field for a large subset of the rows in the table. Since this AREA field only changes when the underlying CONTOUR field changes, is there any way that I can pre-compute the result (ie, at the time of insert/update to the BASE_GEOM table), and simply return this result from memory, rather than calculating the AREA every time it is requested?
I have a feeling the answer might be materialized views, but every example I've seen for materialized views is based on the idea that a query is run at some other time (ie, midnight each night), and on a whole data set, rather than at the time of insert/update and only on a single row.
Thanks,
Sven.

Answer 1

Sven,
The problem is with the SDO_AREA function as can be seen in the result text ("mv references PL/SQL function that maintains state") at the bottom:
/* First create the table */
CREATE TABLE MUSCLE_PSOAS (
  MUSCLE_PSOASID   NUMBER(38),
  RL4AXIALCONTOUR  MDSYS.SDO_GEOMETRY
/* Now the primary key */
ALTER TABLE MUSCLE_PSOAS ADD CONSTRAINT MUSCLE_PSOAS_PK PRIMARY KEY (MUSCLE_PSOASID);
/* Now the MV log */
/* To support all DML (INSERT, UPDATE and DELETE) for FAST REFRESH you must include SEQUENCE and "INCLUDING NEW VALUES" in the MV log. */
CREATE MATERIALIZED VIEW LOG ON MUSCLE_PSOAS
     WITH SEQUENCE, PRIMARY KEY, ROWID
     INCLUDING NEW VALUES;
/* Now create the materialized view */
CREATE MATERIALIZED VIEW MV_DERIVED_MUSCLE_PSOAS
BUILD IMMEDIATE
REFRESH COMPLETE /* Hide "FAST ON COMMIT" to see what MV_Capabilities says... */
WITH PRIMARY KEY
AS
   SELECT mp.rowid as mp_rowid,
          MP.MUSCLE_PSOASID,
          SDO_GEOM.SDO_AREA (mp.RL4AxialContour, 0.005) rl4area
     FROM muscle_psoas mp;
DELETE FROM MV_CAPABILITIES_TABLE;
COMMIT;
execute dbms_mview.explain_mview('MV_DERIVED_MUSCLE_PSOAS');
SELECT capability_name,
       possible,
       related_text,
       msgtxt
  FROM MV_CAPABILITIES_TABLE
WHERE capability_name not like '%PCT%'
   AND capability_name not like 'PCT%'
   AND capability_name not like '%REWRITE%'
   AND capability_name not like 'REWRITE%'
ORDER BY seq;
/* Drop objects */
DROP MATERIALIZED VIEW MV_DERIVED_MUSCLE_PSOAS;
DROP TABLE MUSCLE_PSOAS;Results....
CREATE TABLE succeeded.
ALTER TABLE MUSCLE_PSOAS succeeded.
CREATE MATERIALIZED succeeded.
CREATE MATERIALIZED succeeded.
20 rows deleted
commited
anonymous block completed
CAPABILITY_NAME                POSSIBLE RELATED_TEXT MSGTXT
REFRESH_COMPLETE               Y        NULL         NULL
REFRESH_FAST                   N        NULL         NULL
REFRESH_FAST_AFTER_INSERT      N        NULL         mv references PL/SQL function that maintains state
REFRESH_FAST_AFTER_ONETAB_DML  N        NULL         see the reason why REFRESH_FAST_AFTER_INSERT is disabled
REFRESH_FAST_AFTER_ANY_DML     N        NULL         see the reason why REFRESH_FAST_AFTER_ONETAB_DML is disabled
DROP MATERIALIZED VIEW succeeded.
DROP TABLE MUSCLE_PSOAS succeeded.Now, how can one get it to work? This is how I did it.
/* First create the table */
CREATE TABLE MUSCLE_PSOAS (
  MUSCLE_PSOASID    NUMBER(38),
  rl4area           NUMBER,
  RL4AXIALCONTOUR   MDSYS.SDO_GEOMETRY
/* Now the primary key */
ALTER TABLE MUSCLE_PSOAS ADD CONSTRAINT MUSCLE_PSOAS_PK PRIMARY KEY (MUSCLE_PSOASID);
/* Create Sequence */
Create Sequence MUSCLE_PSOAS_PK_SEQ;
/* Create Trigger for PK and Area */
create or replace trigger MUSCLE_PSOAS_PK_SEQ
before insert or update on MUSCLE_PSOAS
for each row
begin
  if inserting then
    if :NEW.MUSCLE_PSOASID is null then
       select MUSCLE_PSOAS_PK_SEQ.nextval into :NEW.MUSCLE_PSOASID from dual;
    end if;
  end if;
  If :NEW.rl4area is null and :NEW.RL4AXiALCONTOUR is not null then
     :new.rl4area := MDSYS.SDO_GEOM.SDO_AREA(:new.RL4AxialContour, 0.005);
  end if;
end;
show errors
/* Now the MV log */
/* To support all DML (INSERT, UPDATE and DELETE) for FAST REFRESH you must include SEQUENCE and "INCLUDING NEW VALUES" in the MV log. */
CREATE MATERIALIZED VIEW LOG ON MUSCLE_PSOAS
     WITH SEQUENCE, PRIMARY KEY, ROWID
     INCLUDING NEW VALUES;
/* Now create the materialized view */
CREATE MATERIALIZED VIEW MV_DERIVED_MUSCLE_PSOAS
BUILD IMMEDIATE
REFRESH FAST ON COMMIT
WITH PRIMARY KEY
AS
   SELECT mp.rowid as mp_rowid,
          MP.MUSCLE_PSOASID,
          mp.rl4area
     FROM muscle_psoas mp;
DELETE FROM MV_CAPABILITIES_TABLE;
COMMIT;
execute dbms_mview.explain_mview('MV_DERIVED_MUSCLE_PSOAS');
SELECT capability_name,
       possible,
       related_text,
       msgtxt
  FROM MV_CAPABILITIES_TABLE
WHERE capability_name not like '%PCT%'
   AND capability_name not like 'PCT%'
   AND capability_name not like '%REWRITE%'
   AND capability_name not like 'REWRITE%'
ORDER BY seq;
/* Drop objects */
DROP MATERIALIZED VIEW LOG ON MUSCLE_PSOAS;
DROP MATERIALIZED VIEW MV_DERIVED_MUSCLE_PSOAS;
DROP TABLE MUSCLE_PSOAS;
DROP SEQUENCE MUSCLE_PSOAS_PK_SEQ;With the result being:
CREATE TABLE succeeded.
ALTER TABLE MUSCLE_PSOAS succeeded.
Create Sequence succeeded.
TRIGGER MUSCLE_PSOAS_PK_SEQ compiled
No Errors.
CREATE MATERIALIZED succeeded.
CREATE MATERIALIZED succeeded.
14 rows deleted
commited
anonymous block completed
CAPABILITY_NAME                POSSIBLE RELATED_TEXT   MSGTXT
REFRESH_COMPLETE               Y        NULL           NULL
REFRESH_FAST                   Y        NULL           NULL
REFRESH_FAST_AFTER_INSERT      Y        NULL           NULL
REFRESH_FAST_AFTER_ONETAB_DML  Y        NULL           NULL
REFRESH_FAST_AFTER_ANY_DML     Y        NULL           NULL
DROP MATERIALIZED VIEW succeeded.
DROP MATERIALIZED VIEW succeeded.
DROP TABLE MUSCLE_PSOAS succeeded.
DROP SEQUENCE MUSCLE_PSOAS_PK_SEQ succeeded.OK, I know you want to generate the area on the fly - and in this solution an ordinary view will do - but if you need to build fast refresh MVs, the way to do it is:
1. Create the MV REFRESH COMPLETE
2. Then use dbms_mview.explain_mview and MV_CAPABILITIES_TABLE to work out why it will not refresh fast.
3. Play around until you get the required Y against the REFRESH_FAST CAPABILITY_NAME.
4. Deploy
Hope this helps.
regards
Simon