Re: Big Update/DML

Hi,

Runtime is 1:45 hours not 20??
But 1:45 seems still too long.

1. Insert is direct parallel
2. Work distribution is about even
3. Statement scales on CPU

So that is ok.
My gut feeling is that CPUs are not delivering. Could be wrong of course, because I am missing many details. (E.g. how many LOBS are in that table).

1. How many cores do you have that can work on this task?
2. What kind of cores (old sparcs?)
3. What is your compression?

I would run the CTAS without compression. Even if you want the result compressed, you might gain insight.

Regards

Lothar

Am 27.08.2020 um 18:45 schrieb Sanjay Mishra:
> Clay
>
> Thanks for the update. Regarding table, all work for update/CTAS is
> tried only after been refreshed with EXPDP/IMPDP from production to
> test the timeline. I shared the SQL Monitor report in the last email
> and here it is attached again.
>
>
> Sanjay
> On Thursday, August 27, 2020, 12:09:19 PM EDT, Clay Jackson (cjackson)
> <clay.jackson_at_quest.com> wrote:
>
>
> What Lothar said – I’d look at the plan for the CTAS to be sure the
> optimizer isn’t doing something “unusual”,  AND, consider the
> possibility that the table is already horribly “row chained” so that
> each read is actually reading several “random” (or worse)  blocks.  
> More data is clearly key to understanding.
>
> Clay Jackson
>
> *From:* oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org>
> *On Behalf Of *Lothar Flatz
> *Sent:* Thursday, August 27, 2020 3:41 AM
> *To:* oracle-l_at_freelists.org
> *Subject:* Re: Big Update/DML
>
> *CAUTION:*This email originated from outside of the organization. Do
> not follow guidance, click links, or open attachments unless you
> recognize the sender and know the content is safe.
>
> Hi,
>
> with regards to CTAS it is very hard to believe it takes that long. I
> am pretty sure that there is something wrong.
> A sql monitor would be extremly helpfull.
>
> Regards
>
> Lothar
>
> Am 27.08.2020 um 02:43 schrieb Sanjay Mishra (Redacted sender
> smishra_97 for DMARC):
>
> Sayan
>
> Update statement is
>
> Update snows.stamp_detail set set
> stamp_process_calc=processed_calc_amt;
>
> Tried to use
>
> 1. Parallel DML with 100 --> Taking 20+hrs
>
> 2. CTAS was tried using half a billion as well as 1 billion rows
> with parallel 50, 75,100 - Almost same result
>
> 3. CTAS with nologging using same step 2 but still not much
> improvement
>
> We have 5-10 such big table and so running each with this much
> time-frame need high downtime
>
> Tx
>
> Sanjay
>
> On Wednesday, August 26, 2020, 08:23:18 PM EDT, Sayan Malakshinov
> <xt.and.r_at_gmail.com> <mailto:xt.and.r_at_gmail.com> wrote:
>
> Hi Sanjay,
>
> It would be better if you provide more details about your update.
> Exact update statement would be helpful. is this column
> nullable/not null?
>
> On Thu, Aug 27, 2020 at 1:12 AM Sanjay Mishra
> <dmarc-noreply_at_freelists.org <mailto:dmarc-noreply_at_freelists.org>>
> wrote:
>
> Andy
>
> Yes look like is an option if we are doing work online and
> despite take more time but need not require downtime. In our
> case multiple DDL are running to existing environment due to
> Application upgrade and so all work has to be done with
> downtime. So challenge is reduce time of DML operations on big
> tables containing few billions rows.
>
> Tx
>
> Sanjay
>
> On Wednesday, August 26, 2020, 11:20:55 AM EDT, Andy Sayer
> <andysayer_at_gmail.com <mailto:andysayer_at_gmail.com>> wrote:
>
> It does sound like a virtual column could be the ideal
> solution. But if data needs to be physically stored or cannot
> be calculated deterministically at any point in time then
> Connor has a great demo of using dbms_redefinition to create a
> new table online with a function to map the new column.
> There’s obviously some overhead with context switching but it
> may be far better than some of the obstacles you might be
> facing at the moment:
>
> https://connor-mcdonald.com/2016/11/16/performing-a-large-correlated-update/
> <https://nam05.safelinks.protection.outlook.com/?url=https%3A%2F%2Fconnor-mcdonald.com%2F2016%2F11%2F16%2Fperforming-a-large-correlated-update%2F&data=02%7C01%7Cclay.jackson%40quest.com%7Cd7187791c566418711db08d84a75d598%7C91c369b51c9e439c989c1867ec606603%7C0%7C0%7C637341217248530635&sdata=MAHM40uGfFgjYUJGv%2FpEUo7KrT9NgPZvzpF3zASZqTc%3D&reserved=0>
> (and you might be able to help it with pragma udf in the right
> circumstances).
>
> Obviously, how helpful this is depends where the work is
> currently going and how online this needs to be.
>
> Thanks,
>
> Andrew
>
> On Wed, 26 Aug 2020 at 16:00, Jonathan Lewis
> <jlewisoracle_at_gmail.com <mailto:jlewisoracle_at_gmail.com>> wrote:
>
> Is that 3-4 billion rows each, or total ?
>
> I would be a little suspicious of an update which
> populates a new column with a value derived from existing
> columns. What options might you have for declaring a
> virtual column instead - which you could index if needed.
>
> Be extremely cautious about calculating space requirements
> - if you're updating every row on old data might you find
> that you're causing a significant fraction of the rows in
> each block to migrate, and there's a peculiarity of bulk
> row migration that can effectively "waste" 25% of the
> space in every block that becomes the target of a migrated
> row.
>
> This effects can be MUCH work when the table is compress
> (even for OLTP) since the update has to decompress the row
> before updating and then only "re-compresses"
> intermittently as the block becomes full. The CPU cost can
> be horrendous and you still have the problem of migration
> if the addition means the original rows can no longer fit
> in the block.
>
> If it is necessary to add the column you may want to
> review "alter table move online" can do in the latest
> versions (in case you can make it add the column as you
> move) or review the options for dbms_redefinition - maybe
> running several redefinitions concurrently rather than
> trying to do any parallel update to any single table.
>
> Regards
>
> Jonathan Lewis
>
>
> --
>
> Best regards,
> Sayan Malakshinov
>
> Oracle performance tuning engineer
>
> Oracle ACE Associate
> http://orasql.org
> <https://nam05.safelinks.protection.outlook.com/?url=http%3A%2F%2Forasql.org%2F&data=02%7C01%7Cclay.jackson%40quest.com%7Cd7187791c566418711db08d84a75d598%7C91c369b51c9e439c989c1867ec606603%7C0%7C0%7C637341217248540625&sdata=TOD3zIOdZDwp45R4ptmja9tAFNb3DwpnToKef0HMQpI%3D&reserved=0>
>

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