Re: Fixing Performance issue with less selective columns
Date: Wed, 25 Aug 2021 20:14:46 +0200
Message-ID: <a77414ad-7b49-f20c-55de-673fda6aa02b_at_bluewin.ch>
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_at_gmail.com]
> *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_at_rsiz.com
> <mailto:mwf_at_rsiz.com>> 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_at_freelists.org
> <mailto:oracle-l-bounce_at_freelists.org>
> [mailto:oracle-l-bounce_at_freelists.org
> <mailto:oracle-l-bounce_at_freelists.org>] *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_at_gmail.com
> <mailto:loknath.73_at_gmail.com>> 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 <http://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 <http://orasql.org>
>
-- http://www.freelists.org/webpage/oracle-lReceived on Wed Aug 25 2021 - 20:14:46 CEST