Re: Tuning Update query

  Thank you very much for the guidance here.

While going through the code , I noticed that none of the UPDATED columns was getting populated as part of the INSERT query which is populating data in the GTT inside the code. Those are getting populated for the first time through the UPDATE statements i.e. post load. Which means I think, we can outer join those tables(like PRODUCT_TAB) directly in the INSERT query itself and populate the columns rather than doing it after data load.

But then I see there exist one to many relationship between the sources table JOIN(which populates the base data into GTT ) and the PRODUCT_TAB, so it means the outer join is going to break things because the overall number of results set will increase which may not be correct. Or else we may have to use a DISTINCT clause to get those corrected.

Regards
Lok

On Tue, May 4, 2021 at 5:03 PM Mark W. Farnham <mwf_at_rsiz.com> wrote:

> Do you have handy the script or load used to create GTT_TAB?
>
>
>
> It seems passing strange that you want to debug what is essentially a row
> by row case computation instead of creating the disjoint sets of rows to
> operate on as a bulk set.
>
>
>
> Consider GTT_TAB_XX_Y alias XX_Y, which contains only TMP.CIND=’Y’ and
> TMP.PART_DT for which the corresponding TMP.PART_DT = P.PART_DT has
> P.CODE=’XX’.
>
>
>
> Then insert into GTT_TAB
>
>
>
> Select p.<the column list from P>, xx_y.<the column list from XX_Y> where
> p.tid=xx_y.tid and p.part_dt=xx_y.part_id
>
>
>
> All the rows from xx_y are used and should be a full table scan, matching
> against the presumably indexed p.tid, p.partid from P.
>
>
>
> Do this for each of your separate “updates”, appending into GTT_TAB, and
> directly append the disjoint bits that require no update directly into
> GTT_TAB however you do now. The only tricky set is P.CODE=’AA’ for which
> you have two updates. For that, use GTT_TAB_AA_5 gets appended into
> GTT_TAB_AA_6 and GTT_TAB_AA_6 gets appended into GTT_TAB.
>
>
>
> All the other rows (which meet zero of your update predicates) you dump
> directly into GTT_TAB from wherever you are currently plucking them.
>
>
>
> This of course fixes your ‘Y’ problem and operates set wise using bulk
> inserts AND operates only on rows that need attention instead of filtering
> out the rows you’re not interested in for each update.
>
>
>
> Write out the differences as a dataflow diagram to understand why this
> always wins.
>
>
>
> mwf
>
>
>
> *From:* oracle-l-bounce_at_freelists.org [mailto:
> oracle-l-bounce_at_freelists.org] *On Behalf Of *Jonathan Lewis
> *Sent:* Tuesday, May 04, 2021 5:07 AM
> *To:* Lok P
> *Cc:* Oracle L
> *Subject:* Re: Tuning Update query
>
>
>
>
>
> a) I wasn't suggesting that you use an updatable join view, but I can see
> how you could misinterpret what I said. The idea was to see if you could
> write a single subquery that joined several of the source tables (such as
> PRODUCT_TAB) and then still carry out that full tablescan of the GTT but
> using that join as your subquery update rather than having "one tablescan
> and update = one subquery".
>
>
>
> I see you're already doing something of this kind using the MERGE command;
> if you're getting an ORA-01779 when you try to rewrite one of your updates
> as an update through an updatable join view this means that equivalent code
> to do a MERGE could produce a run-time error ORA-30926). The update portion
> of a merge and an updatable join view both require the same uniqueness but
> the view enforces the logical requirement at compile time while the merge
> command allows you to get away with the update so long as you get lucky
> with the data.
>
>
>
> I note that you still haven't moved the "tmp.cind = 'Y'" predicate to the
> correct position - that should have been the zeroth step before worrying
> about anything else. I assume the one update I picked out isn't the only
> one where this error occurs.
>
>
>
>
>
> b) Correct regarding multiple GTTs. Each "insert /*+ append */" would
> probably require it's own target GTT. Remember, though, that I haven't
> examined your original posting in detail, and you probably haven't told us
> everything a consultant would ask about so if your current code has some
> parts that update disjoint subsets of the data you might find parts of the
> rewrite where you could do multiple inserts into the same GTT.
>
>
>
> One thing to bear in mind - a possible bar to adopting this approach - is
> that you would have to commit after insert otherwise the next insert, or
> the next query against the target GTT would raise the (unexpectedly
> parallel) error: ORA-12838: cannot read/modify an object after modifying
> it in parallel
>
>
>
> Regards
>
> Jonathan Lewis
>
>
>
>
>
>
>
>
>
>
>
> On Mon, 3 May 2021 at 12:58, Lok P <loknath.73_at_gmail.com> wrote:
>
> Thank You Jonathan and Lothar. I was trying to modify one of the sample
> updates(as below) as per your suggested method.
>
>
>
> UPDATE GTT_TAB TMP
>
> SET (c1, c2, c3, c4,c5.. c11) =
>
> ( (SELECT col1,col2,..col11
>
> FROM PRODUCT_TAB P
>
> WHERE P.TID = TMP.TID
>
> AND TMP.CIND = 'Y'
>
> AND P.PART_DT = TMP.PART_DT
>
> AND P.CODE = 'XX'))
>
>
>
> Jonathan, let me know if my understanding is correct on the suggested
> points
>
> *" a) See if you can minimise the number of update ste[ps by updating from
> a JOIN of several source tables" *
>
>
>
> So if I get the above point correct then I was trying to modify the UPDATE
> as below , but I am getting ORA-01779 while running to see the plan. So
> does it mean that the GTT has to have a unique key present in it to have
> this method work?
>
>
>
> UPDATE (SELECT P.COL1...P.col11,TMP.C1.. TMP.C11
>
> FROM PRODUCT_TAB P,GTT_TAB TMP
>
> WHERE P.TID = TMP.TID
>
> AND TMP.CIND = 'Y'
>
> AND P.PART_DT = TMP.PART_DT
>
> AND P.CODE = 'XX'
>
> ) SET C1=COL1, ... C11=COL11;
>
> ERROR at line 10:
>
> ORA-01779: cannot modify a column which maps to a non key-preserved
> table
>
>
>
> Regarding below point ,
>
> *"b) Rewrite the code to step through a series of GTT doing*
>
> * insert /*+ append */ into next_gtt select from previous_gtt join
> {source tables}"*
>
>
>
> Do you mean i have to replace the UPDATE with INSERT /*+APPEND*/...
> queries but as it cant be done in the same GTT , so i have to create
> multiple GTT's for each UPDATES, so as to replace them with INSERT APPEND
> queries?
>
>
>
>
>
>

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