Re: Cause behind execution plan change

You shouldn't be using the ORDERED hint, by the way, you should learn how to use the LEADING() hint.
And since you've dictated the join order for this query FT does not need to be in the USE_NL() hint because it's the first table in the join order so it's not going to appear as the second table in any of the joins. (See: https://jonathanlewis.wordpress.com/2017/01/13/use_nl-hint/ , and for the equivalent comment on the use_hash() hint see: https://jonathanlewis.wordpress.com/2013/09/07/hash-joins/ )

Regards
Jonathan Lewis

On Sun, 18 Jul 2021 at 20:35, Pap <oracle.developer35_at_gmail.com> wrote:

> Hello listers, It's version 12.1.0.2.0 of oracle. We have done a change
> to the code inside the function which gets called from the SELECT query.
> But as its just been used in the SELECT part of the query ideally it should
> not change sql_id of the query and also the plan, but we also add one new
> additional input parameter(i.e. :B3 below) to the function call and thus
> sql_id got changed which is understood. But something which we are not able
> to understand is , why did the plan change occurred after this change?
>
> Attached is both the plans i.e the one it used to take in the past vs the
> current one which it's now taking. From the plan it does look like , its
> cardinality estimation of global temporary table FT which causes the
> difference, as it puts table RTNID in index access vs FTS access in a
> nested loop. But the old query(before function change) was not taking the
> bad plan ever, but it started taking after function change. So wondering
> how a new input parameter addition to a function which is not part of the
> WHERE clause, can cause this sort of impact and how to fix it?
>
> In this query, all the tables are global temporary tables except FFT,
> which is a list partition table with partition key as CKEY.
>
> INSERT INTO RTF(...)
> SELECT /*+ ordered use_nl(ft FFT nd curr)*/ ND.NE, ND.NID, CUR.SCD,
> FT.FXID, FT.TFXID,
> fun1 (FFT.AMT, FT.STS, FT.PDT, :B3, TRUNC ( :B2), 'S'),
> fun1 (FFT.AMT, FT.STS, FT.PDT, :B3, TRUNC ( :B2), 'F'),
> TRUNC ( :B1),
> ND.MCID
> FROM FT , FFT , RTNID ND, RDCUR CUR
> WHERE FT.FFXID = FFT.FXID
> AND FT.ACK = FFT.CK
> AND FFT.CKEY = ND.NKEY
> AND ND.NE IN ('XX', 'YY', 'ZZ')
> AND FFT.STCD IN ('X', 'Y')
> AND FFT.CKEY = CUR.CKEY
>
>
>
>
>

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