I only want to support what Sayan has said about the result cache that can
cause *Result Cache: RC Latch* when the result of the function call is
invalidated for one reason or another. Here’s below a practical case of the
wrong usage of the *result_cache hint* which can give you an idea about its
effect when you would use it in your function or cache the result of your
function call.
https://hourim.wordpress.com/2018/08/17/wrong-utilisation-of-result-cache/
As for the idea of surrounding the call to your function with a *select
from dual*, I think that's a good idea. Here is another example taken from
a real-life running system that shows the benefit of Scalar Subquery Caching
https://hourim.wordpress.com/2019/12/18/scalar-subquery-caching-the-select-from-dual-trick/
Best regards
Mohamed Houri
Le sam. 30 oct. 2021 à 04:58, Lok P <loknath.73@xxxxxxxxx> a écrit :
Thank You So much Sayan and Jonathan.
Along with the to_char changes. I will also try to see the performance of
one test case with a combination of both i.e. SSC in the main query(i.e.
wrapping fun1 in select..from dual) And deterministic function and pragma
UDF in the function code. Will try to see if it's giving the best of both
features.
On Sat, Oct 30, 2021 at 3:05 AM Jonathan Lewis <jlewisoracle@xxxxxxxxx>
wrote:
To add to Sayan's comment about eliminating the select from dual: you're
also wasting CPU converting between date and character - sticking with date
arithmetic is likely to be more efficient (and arguably easier to
understand):
IF to_char(INPDT, 'HH:MI:SS AM') = '12:00:00 AM' then
SELECT TO_DATE(TO_CHAR(INPDT,'MM/DD/YYYY') || ' ' ||
TO_CHAR(IN_STDT, 'HH:MI:SS AM'), 'MM/DD/YYYY HH:MI:SS AM') INTO o_pdt FROM
DUAL;
ELSE
o_pdt := INPDT;
END IF;
--
if inpdt = trunc(inpdt) then
o_pdt := inpdt + (in_stst - trunc(in_stdt));
else
o_pdt := inpdt;
end if;
You might note that another option to reduce PL/SQL overheads is to use
the "with function" feature that appeared in 12c
(see, for example,
https://jonathanlewis.wordpress.com/2013/06/30/12c-fun/ ;) Though if your
function is used in many different SQL statements you might still want to
keep it as a standalone PL/SQL function declared with pragma UDF.
Determinism vs. scalar subquery caching - the scalar subquery cache is
fairly limited in size, and you can be unlucky with hash collisions; so
your best bet is to follow Sayan's advice to start with; but it shouldn't
take much effort to test both options.
Regards
Jonathan Lewis
On Fri, 29 Oct 2021 at 20:44, Lok P <loknath.73@xxxxxxxxx> wrote:
Hello Listers, We have below Insert query which is executed ~50k - 60K
times each day. And this is consuming major amount of time in a specific
process/procedure which in turns gets called from multiple scenarios. And
while looking into the sql monitor we saw its majorly CPU time and its in
the loading part only(~350 secs), which seems to be coming from the
function call in the SELECT part of the insert query. As shown in the sql
monitor this function seems to be getting called atleast ~8million times
here one time for each row for this single execution of the main insert
query. I have posted the function code here below. So in total this
function call seems to be happening billions of time in a day. Its oracle
database version 19.9.0.0.0. I never used but heard of few option in such
cases like scalar subquery caching, Result cache, deterministic function
etc. So wanted to understand, if wrapping up this function call in a
"select from dual" i.e utilizing scalar subquery caching technique will
help us here? Or as the function body doesn't depend on any DB tables etc,
a results cache should be opted here? What should be the best option here?
We have currently having below result cache option as i see in
v$parameter.
NAME VALUE
result_cache_mode MANUAL
result_cache_max_size 107380736
result_cache_max_result 5
result_cache_remote_expiration 0
client_result_cache_size 0
client_result_cache_lag 3000
*Main query:-*
INSERT INTO GLBL_TMP_TBL1 (.........)
SELECT............
pkg.fun1 (RFFT.AMT, RTFX.STS, RTFX.PDT, :B1, ( :B1 + 1),
'X'),
pkg.fun1 (RFFT.AMT, RTFX.STS, RTFX.PDT, :B1, ( :B1 + 1), 'Y'),
TRUNC ( :B1)....
FROM RTFX RTFX, RFFT RFFT, ND ND, RDC RDC
WHERE RTFX.FFXID = RFFT.FXID
AND RTFX.AC_Key = RFFT.C_Key
AND RFFT.CT_Key = ND.N_Key
AND ND.N_ETY IN ('XX', 'YY', 'ZZ')...;
*Function code:- *
FUNCTION fun1(INAMT IN NUMBER, INSTS IN VARCHAR2, INPDT IN
DATE,IN_STDT IN DATE, IN_ENDT IN DATE, INBK IN VARCHAR2) RETURN
NUMBER IS
o_pdt DATE;
BEGIN
IF INBK = 'Y' THEN
IF (INSTS = 'AA' AND INPDT > IN_ENDT) THEN
RETURN INAMT ;
END IF;
IF (INSTS IN ('SS','BB', 'TT','ZZ')) THEN
RETURN INAMT ;
END IF;
ELSIF (INBK = 'X')
THEN
IF to_char(INPDT, 'HH:MI:SS AM') = '12:00:00 AM' then
SELECT TO_DATE(TO_CHAR(INPDT,'MM/DD/YYYY') || ' ' ||
TO_CHAR(IN_STDT, 'HH:MI:SS AM'), 'MM/DD/YYYY HH:MI:SS AM') INTO o_pdt FROM
DUAL;
ELSE
o_pdt := INPDT;
END IF;
IF (INSTS = 'AA' AND o_pdt >= IN_STDT AND o_pdt < IN_ENDT)
THEN
DBMS_OUTPUT.PUT_LINE(o_pdt || ' - ' || INAMT);
RETURN INAMT ;
END IF;
END IF;
RETURN 0;
END;
/
Global Information
------------------------------
STATUS : DONE
Instance ID : 4
SQL Execution ID : 67303461
Execution Started : 10/29/2021 07:03:58
First Refresh Time : 10/29/2021 07:04:02
Last Refresh Time : 10/29/2021 07:16:19
Duration : 741s
Global Stats
=======================================================================================================
| Elapsed | Cpu | IO | Concurrency | Cluster | PL/SQL | Other |
Buffer | Read | Read |
| Time(s) | Time(s) | Waits(s) | Waits(s) | Waits(s) | Time(s) |
Waits(s) | Gets | Reqs | Bytes |
=======================================================================================================
| 742 | 704 | 35 | 0.17 | 0.00 | 157 | 3.07 |
11M | 67661 | 529MB |
=======================================================================================================
SQL Plan Monitoring Details (Plan Hash Value=3120541595)
======================================================================================================================================================================================================================
| Id | Operation | Name
| Rows | Cost | Time | Start | Execs | Rows | Read | Read
| Activity | Activity Detail |
| | |
| (Estim) | | Active(s) | Active | | (Actual) | Reqs
| Bytes | (%) | (# samples) |
======================================================================================================================================================================================================================
| 0 | INSERT STATEMENT |
| | | 738 | +4 | 1 | 0 | |
| 20.82 | Cpu (152) |
| 1 | LOAD TABLE CONVENTIONAL | GLBL_TMP_TBL1
| | | 741 | +1 | 1 | 0 | |
| 32.33 | Cpu (236) |
| 2 | NESTED LOOPS |
| 115 | 86999 | 738 | +4 | 1 | 8M | |
| 0.27 | Cpu (2) |
| 3 | NESTED LOOPS |
| 115 | 86999 | 738 | +4 | 1 | 8M | |
| | |
| 4 | NESTED LOOPS |
| 115 | 86884 | 738 | +4 | 1 | 8M | |
| 0.27 | Cpu (2) |
| 5 | NESTED LOOPS |
| 4405 | 82363 | 738 | +4 | 1 | 8M | |
| | |
| 6 | TABLE ACCESS STORAGE FULL | RTFX
| 3291 | 14 | 738 | +4 | 1 | 4250 | |
| | |
| 7 | PARTITION LIST ITERATOR |
| 1 | 25 | 738 | +4 | 4250 | 8M | |
| | |
| 8 | TABLE ACCESS BY LOCAL INDEX ROWID BATCHED | RFFT
| 1 | 25 | 738 | +4 | 4249 | 8M | 55950 |
437MB | 5.48 | Cpu (11) |
| | |
| | | | | | | |
| | cell single block physical read (29) |
| 9 | INDEX RANGE SCAN | RFFT_IX1
| 836 | 4 | 738 | +4 | 4249 | 8M | 9331 |
73MB | 1.37 | Cpu (5) |
| | |
| | | | | | | |
| | cell single block physical read (5) |
| 10 | TABLE ACCESS BY INDEX ROWID BATCHED | ND
| 1 | 2 | 738 | +4 | 8M | 8M | |
| 3.15 | Cpu (23) |
| 11 | INDEX RANGE SCAN | ND_IX6
| 1 | 1 | 738 | +4 | 8M | 8M | |
| 2.74 | Cpu (20) |
| 12 | INDEX UNIQUE SCAN | RDC_PK
| 1 | | 742 | +0 | 8M | 8M | |
| 0.55 | Cpu (4) |
| 13 | TABLE ACCESS BY INDEX ROWID | RDC
| 1 | 1 | 738 | +4 | 8M | 8M | |
| 3.15 | Cpu (23) |
======================================================================================================================================================================================================================
