Thank You Andy. Actually as I stated earlier, this query is executed in a
few seconds only but it's the higher number of executions(thousands+) for
different binds which add up to the overall long run time of the process.
and also most of the runs result in zero rows only. I tried putting
it/query in a loop for different binds and executed with parallel (i 4)
and without parallel and it seems it's taking longer with parallel hints.
It may be because of maintaining and aggregating those additional
parallel slaves etc.
*"Is :b4:= 'A' representative of your typical query here?" *apology for
the confusion, actually i was trying to camouflage the actual bind values
and that made it confusing. So it's actually coming as 'D' i.e. having
~104million matching rows in that table. So indexing that won't help here
too.
The column M_TXT, its VARCHAR2(100 byte) column and holding string values
with many having spaces in it at start/last.So trim function
seems necessary.This filter alone is making the result set to ZERO for this
query and its having highest NUM_DISTINCT values too, so it seems good
candidate here for index. And this filter With regards to
substr(:B8,.50), I will confirm and try to get it removed as that doesn't
seem to serve any purpose but was somehow is there in this legacy code. We
should be able to simply remove that SUBSTR function without any issue. But
irrespective of that SUBSTR function on the right hand side of the
predicate, are you pointing towards creating a function based index on
trim(M_TXT) at the left hand side to help this query? Actually , I saw in
many other places , this column is utilized in the predicates section like
*substr(trim(m_txt),2,20)*=decode(col1, 'YYY', substr('XXXXX',1,20)). So is
it possible to just have one index to cater both scenarios or we can tweak
the query someway so as to utilize the same index for all the queries on
this string column?
On Thu, Aug 26, 2021 at 12:12 AM Andy Sayer <andysayer@xxxxxxxxx> wrote:
Hi Lok,
" If there exists any other way to make this query faster without
creating any new index that would really be helpful."
You can use parallelism and have the scan completed by more processes at
once.
Is :b4:= 'A' representative of your typical query here? The results
you've shared suggest this will return 0 rows, however there aren't a lot
of distinct values for DC_CODE and you don't have any statistics. If the
argument is frequently used then an index and a frequency histogram on this
column would be lucrative. It's a bit surprising you have so many
histograms on this table but this column's statistics didn't appear.
The filter on M_TXT also would provide decent selectivity, I would
question whether the trim is really needed. The substr 0.5 is a huge red
flag.
Thanks,
Andrew
On Wed, 25 Aug 2021 at 19:14, Lothar Flatz <l.flatz@xxxxxxxxxx> wrote:
This scenario cries for bitmap indexes.
Bitmap Indexes can deal with "not equal" as well as "is null".
The columns seems to be low cardinality too.
The only open question is how often these columns get updated. (
https://asktom.oracle.com/pls/apex/asktom.search?tag=bitmap-indexes-and-locking
).
Regards
Lothar
Am 25.08.2021 um 19:19 schrieb Mark W. Farnham:
unfortunately you keep nearly all the rows of both MA_FLG and D_UNMTCH,
so this query is the opposite of those indexes being useful.
IF you were looking for ‘Y’ instead of not ‘Y’ on either one it would be
extremely good. I didn’t see initially that these two columns are extremely
inclusive.
I think Sayan was checking that in his query request. MA_FLG could reject
at most about 6 million rows, so that’s pretty worthless.
*From:* Lok P [mailto:loknath.73@xxxxxxxxx ;<loknath.73@xxxxxxxxx>]
*Sent:* Wednesday, August 25, 2021 1:09 PM
*To:* Mark W. Farnham
*Cc:* Sayan Malakshinov; Oracle L
*Subject:* Re: Fixing Performance issue with less selective columns
Thank You Mark.
I may be wrong but in this situation I was unable to think of any other
way we could make this query faster , so I was thinking of creating a new
index. If there exists any other way to make this query faster without
creating any new index that would really be helpful.
I am not able to get your point fully, If you can help me understand it a
bit more here please. Below is the data pattern for MA_FLG and D_UNMTCH.
Thus , in this query condition " NVL (I.MA_FLG, 'N') <> 'Y' results in
~105million and NVL (I.D_UNMTCH, 'N') <> 'Y' results in ~111million. So
how should I create index or modify code to make it the best access/filter
criteria so as to make the query faster?
MA_FLG
Count(*)
N
105228656
Y
6000938
643566
D_UNMTCH
Count(*)
Y
13715
111859445
On Wed, Aug 25, 2021 at 8:00 PM Mark W. Farnham <mwf@xxxxxxxx> wrote:
The other thing, for flag values like AND NVL (I.MA_FLG, 'N') <>
'Y' AND NVL (I.D_UNMTCH, 'N') <> 'Y'
if you’re thinking about adding an index, and even if you need a virtual
column to do this because you have too much code depending on values ‘N’
and ‘Y’, define the final status (the one where nearly all of them land) as
NULL, being the ones you are NOT interested in most of the time. In both
these cases it looks like ‘Y’ would then be NULL, so
i.ma_flg_v is defined decoding Y to NULL and anything else to N and your
code becomes and i.ma_flg_v = ‘N’ and you deal with variability in
non-nulls that are not ‘Y’ on the original,
or
i.ma_flg_v decodes Y to NULL, NULL to ‘N’ and anything else unchanged and
your code becomes i.ma_flg_v is NOT NULL,
or
you make a functional index on i.ma_flg that does the equivalent.
I can’t remember off the top of my head whether either way gives you a
real advantage over the other in stats collections and the CBO doing
something smart and that probably changed over the releases. That might be
in one of my papers.
When you then index that column the nulls disappear, leaving you with a
very tiny index to prune your result set immediately to very small and you
can usually filter the rest fast without an index.
Remember, ORACLE cannot assign a value to NULL in anything they do. But
YOU can.
When this is appropriate, it is one of the neatest and easiest “magic
tricks” in the Oracle kit.
Good luck,
mwf
*From:* oracle-l-bounce@xxxxxxxxxxxxx [mailto:
oracle-l-bounce@xxxxxxxxxxxxx] *On Behalf Of *Sayan Malakshinov
*Sent:* Wednesday, August 25, 2021 9:40 AM
*To:* Lok P
*Cc:* Oracle L
*Subject:* Re: Fixing Performance issue with less selective columns
Hi Lok,
SUBSTR(:B8,0*.50*)
Looks like this query should be analyzed and tested better.
You haven't provided histograms and bind values statistics, so not
enough info to analyze it properly.
For now it looks like "I.WOF_DATE IS NULL" is one of the most selective
predicates - it gives only 83154 nulls.
In addition to histogram statistics(dba_tab_histograms) and most often
binds values, I would like also to see what does return this query:
select
NVL(I.MA_FLG, 'N'),NVL(I.D_UNMTCH, 'N'),I.DC_CODE,count(*)
FROM PP_IN_TAB I
group by NVL(I.MA_FLG, 'N'),NVL(I.D_UNMTCH, 'N'),I.DC_CODE;
On Wed, Aug 25, 2021 at 4:14 PM Lok P <loknath.73@xxxxxxxxx> wrote:
Hello , This database has version 11.2.0.4 of Oracle. We have the below
query which is executed thousands of times. It's used in a plsql function
which in turn gets called from a procedure. And this procedure gets called
from java thousands of times. And I see from dba_hist_sqlstat , for most
of the runs this below query results in zero rows. We see from the active
session history for the overall process this query is consuming most
time/resources and making the process run longer. So wanted to understand
if we can make this individual query execution faster which would
eventually make the process faster?
The base table- PP_IN_TAB is holding ~111million rows and is ~43GB in
size. Column PP_ID is the primary key here. The filter predicates used in
this query are below. Many of them were not very selective in nature. So I
am not able to conclude if any composite index is going to help us here.
Can you please guide me , what is the correct approach to tune this process
in such a scenario?
Below is the column data pattern used as filter predicate in this query.
Most of these are less selective in nature.
*TABLE_NAME*
*COLUMN_NAME*
*NUM_DISTINCT*
*NUM_NULLS*
PP_IN_TAB
EF_ID
39515
6151686
PP_IN_TAB
PE
103074806
647050
PP_IN_TAB
PT_Code
24
0
PP_IN_TAB
PT_MCODE
20
0
PP_IN_TAB
D_CUR_CODE
13
592784
PP_IN_TAB
ED_AMT
320892
6
PP_IN_TAB
WOF_DATE
2572
83154
PP_IN_TAB
PR_CTGRY
2
86
PP_IN_TAB
PDE_RSN_CAT
6
0
PP_IN_TAB
MA_FLG
2
648172
PP_IN_TAB
M_TXT
29460248
9118572
PP_IN_TAB
D_UNMTCH
1
111766716
SELECT NVL (I.PP_ID, 0)
FROM PP_IN_TAB I
WHERE TRIM(I.M_TXT) = TRIM (SUBSTR ( :B8, 0.50)) AND I.PT_Code
= :B7
AND NVL ( :B6, I.PT_MCODE) = NVL ( :B6, :B5) AND I.DC_CODE =
:B4
AND I.D_CUR_CODE = :B3 AND I.ED_AMT = :B2
AND I.PR_CTGRY = :B1 AND I.PE IS NOT NULL
AND I.EF_ID IS NULL AND I.WOF_DATE IS NULL
AND NVL (I.MA_FLG, 'N') <> 'Y' AND NVL (I.D_UNMTCH, 'N') <>
'Y'
AND ROWNUM = 1;
Global Information
------------------------------
Status : DONE (ALL ROWS)
Instance ID : 1
SQL Execution ID : 16777216
Execution Started : 08/25/2021 03:53:25
First Refresh Time : 08/25/2021 03:53:25
Last Refresh Time : 08/25/2021 03:53:28
Duration : 3s
Module/Action : SQL*Plus/-
Program : sqlplus.exe
Fetch Calls : 1
Global Stats
=========================================================================================
| Elapsed | Cpu | IO | Application | Fetch | Buffer | Read |
Read | Cell |
| Time(s) | Time(s) | Waits(s) | Waits(s) | Calls | Gets | Reqs |
Bytes | Offload |
=========================================================================================
| 3.30 | 1.15 | 2.15 | 0.00 | 1 | 6M | 44379 |
43GB | 99.99% |
=========================================================================================
SQL Plan Monitoring Details (Plan Hash Value=1096440065)
==========================================================================================================================================================================================
| Id | Operation | Name | Rows | Cost |
Time | Start | Execs | Rows | Read | Read | Cell | Mem |
Activity | Activity Detail |
| | | | (Estim) | |
Active(s) | Active | | (Actual) | Reqs | Bytes | Offload | (Max) |
(%) | (# samples) |
==========================================================================================================================================================================================
| 0 | SELECT STATEMENT | | | |
| | 1 | | | | | |
| |
| 1 | COUNT STOPKEY | | | |
| | 1 | | | | | |
| |
| 2 | TABLE ACCESS STORAGE FULL | PP_IN_TAB | 1 | 128K |
3 | +2 | 1 | 0 | 44379 | 43GB | 99.99% | 6M |
100.00 | cell smart table scan (3) |
==========================================================================================================================================================================================
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(ROWNUM=1)
2 - storage("I"."WOF_DATE" IS NULL AND "I"."EF_ID" IS NULL AND
"I"."PT_Code"=:B7 AND "I"."D_CUR_CODE"=:B3 AND "I"."PR_CTGRY"=:B1 AND
"I"."DC_CODE"=:B4 AND "I"."ED_AMT"=TO_NUMBER(:B2) AND
NVL(:B6,"I"."PT_MCODE")=NVL(:B6,:B5) AND
TRIM("I"."M_TXT")=TRIM(SUBSTR(:B8,0.50))
AND "I"."PE" IS NOT NULL AND NVL("I"."MA_FLG",'N')<>'Y' AND
NVL("I"."D_UNMTCH",'N')<>'Y')
filter("I"."WOF_DATE" IS NULL AND "I"."EF_ID" IS NULL AND
"I"."PT_Code"=:B7 AND "I"."D_CUR_CODE"=:B3 AND "I"."PR_CTGRY"=:B1 AND
"I"."DC_CODE"=:B4 AND "I"."ED_AMT"=TO_NUMBER(:B2) AND
NVL(:B6,"I"."PT_MCODE")=NVL(:B6,:B5) AND
TRIM("I"."M_TXT")=TRIM(SUBSTR(:B8,0.50))
AND "I"."PE" IS NOT NULL AND NVL("I"."MA_FLG",'N')<>'Y'
AND NVL("I"."D_UNMTCH",'N')<>'Y')
--
Best regards,
Sayan Malakshinov
Oracle performance tuning engineer
Oracle ACE Associate
http://orasql.org
