KSCOPE Answer 2 of 2 – Part 1

Another question I was asked at KSCOPE 2019 was if Polymorphic Table Functions (PTF) could mimic an SQL CONNECT BY query. The question borders between a real world usage and a home work assignment but I’ll give the benefit of the doubt and turn it into the next series of posts on performance.

Here is the SQL CONNECT BY query.

SELECT partno p,
       sdate,
       edate,
       level  l,
       SYS_CONNECT_BY_PATH(sdate, '/') path
  FROM prices
 START WITH TRUNC(sdate) = TRUNC(sysdate)
 CONNECT BY PRIOR edate  = sdate AND
   PRIOR partno = partno;

P SDATE     EDATE     L PATH
- --------- --------- - ------------------------------
1 02-AUG-19 12-AUG-19 1 /02-AUG-19
1 12-AUG-19 22-AUG-19 2 /02-AUG-19/12-AUG-19
1 22-AUG-19 01-SEP-19 3 /02-AUG-19/12-AUG-19/22-AUG-19
2 02-AUG-19 12-AUG-19 1 /02-AUG-19
2 12-AUG-19 22-AUG-19 2 /02-AUG-19/12-AUG-19

It works through a table of part prices to assemble a price history per part.

And here is the beginnings of a PTF to mimic it.

CREATE OR REPLACE PACKAGE ptf_pkg AS
  FUNCTION describe (p_tbl IN OUT DBMS_TF.TABLE_T )
           RETURN DBMS_TF.DESCRIBE_T;
END;

CREATE OR REPLACE PACKAGE BODY ptf_pkg AS
  FUNCTION describe (p_tbl IN OUT DBMS_TF.TABLE_T )
           RETURN DBMS_TF.DESCRIBE_T IS 
  BEGIN
    RETURN NULL;
  END;
END;

CREATE OR REPLACE FUNCTION ptf_func(p_tbl IN TABLE )
  RETURN TABLE PIPELINED
  TABLE POLYMORPHIC USING ptf_pkg;

I have specified TABLE POLYMORPHIC so that I can group the queried data.

And here is the PTF query partitioning and ordering the results automatically.

SELECT *
  FROM ptf_func(prices PARTITION BY partno
ORDER BY sdate );

PARTNO SDATE     EDATE     PRICE
------ --------- --------- -----
     1 02-AUG-19 12-AUG-19   100
     1 12-AUG-19 22-AUG-19   200
     1 22-AUG-19 01-SEP-19   500
     2 02-AUG-19 12-AUG-19    33
     2 12-AUG-19 22-AUG-19    31

Only the directly queried columns match the CONNECT BY ones at this point. Before I go any further I’ll compare performance because I don’t want to waste time if its slower right out of the gate.

I’ll generate test data with this PL/SQL.

DECLARE
  v_sdate DATE;
  v_edate DATE;
BEGIN
  -- for every freaking part...
  FOR part IN 1..<part> LOOP
    v_sdate := SYSDATE;
    v_edate := SYSDATE + 3;
    -- for every row of prices I want to add...
    FOR counter IN 1..<price> LOOP
      INSERT INTO prices
      VALUES(<part>,v_sdate,v_edate,100);
      v_sdate := v_edate;
      v_edate := v_sdate + 3;
    END LOOP;  -- every price row
  END LOOP;  -- every freaking part
END;

I’ll use 1,000 parts with 100 prices each for my test runs.

Here are the results from SQL Trace for 3 executions of the CONNECT BY query.

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        3      0.00       0.00          0         72          0           0
Execute      3      0.00       0.00          0          0          0           0
Fetch    20004      4.70       5.08          0     134229          0      300000
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total    20010      4.71       5.09          0     134301          0      300000

Here are the results for 3 executions of the PTF.

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        3      0.03       0.02          0        200          0           0
Execute      3      0.00       0.00          0          0          0           0
Fetch    20004      2.33       2.78          0      99785          0      300000
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total    20010      2.36       2.81          0      99985          0      300000

The most interesting numbers are the CPU and elapsed time.

  • CPU is 2.36 for the PTF vs 4.71 for the CONNECT BY (50% faster)
  • ELA is 2.81 for the PTF vs vs 5.09 for the CONNECT BY (45% faster)

Will these results hold as I add the actual CONNECT BY behaviour? We’ll find out as I work through it in the next few posts.

Thanks for reading!