RE: No Row Chaining "Bug" ?

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Thu, 21 May 2015 06:48:16 +0000
Message-ID: <CE70217733273F49A8A162EE074F64D92828EC3B_at_EXMBX01.thus.corp>


Looking at the bug and the referenced doc about the hidden parameter, I'd guess someone did a misleading test and came to the wrong conclusion.

A row with 999 columns with a numeric 999th column set to zero and all the rest null would have a row length (on some counts) of 1,000 so falls into that grey area where Oracle might or might not insert it into a different block.

We also have the problem of the way Oracle has introduced some changes in the way it counts continued rows when handling intra-block chaining, and the last time I checked there were still some inconsistencies in the counting.

Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
_at_jloracle



From: oracle-l-bounce_at_freelists.org [oracle-l-bounce_at_freelists.org] on behalf of Chitale, Hemant K [Hemant-K.Chitale_at_sc.com] Sent: 21 May 2015 02:56
To: Kenny Payton
Cc: ORACLE-L
Subject: RE: No Row Chaining "Bug" ?

Yes, I came across this earlier :
Bug 9373758 - Optimization to handle insert of >255 columns (Doc ID 9373758.8)

Salem Ghassan also said that 20901134 was closed as Not a Bug and referred me back to 9373758.

Hemant K Chitale

From: Kenny Payton [mailto:k3nnyp_at_gmail.com] Sent: Wednesday, May 20, 2015 8:13 PM
To: Chitale, Hemant K
Cc: ORACLE-L
Subject: Re: No Row Chaining "Bug" ?

Not for sure where the 999 comes from but take a look at bug #9373758 and the following parameter added in 11.2.0.4.4 and 12???? This appears to work for inserts, although subsequent updates seem to still become multiple row pieces.

"_rowlen_for_chaining_threshold"

I posted the below to this list in Jan.

"

I canít believe Iíve put this off since April, although not a coincidence that my company was acquired in May.

I was finally able to test the hidden parameter and it works ( mostly ). I used imp, trying to keep it simple, to load 100k rows that were plagued with populated column IDís > 255. With the parameter set to 0, simulating pre-parameter, the data loaded with 3,420 chained rows. After setting the parameter to 8000, with a 8k block size database, I reloaded the data and although I expected the chained rows to be 0 it left 29. I have yet to explain the 29 since they are not too large to fit in a block, average row size of 852, and were less than the 8000 I set the parameter to. After a CTAS of the previously loaded table the new resulting table with the same 100k rows returned 0 chained rows. I ran the load process a number of times consistently with the same results.

Nonetheless, although not perfect it seems to make a significant dent in the number of inter block chained rows and after some additional testing we will be excited to get this into production. If I can find some time to dig deeper in this Iíll try to dump the block and see what is going on.

In case you were wondering, here is the parameter. _rowlen_for_chaining_threshold

Thanks again Gaja for pointing out the bug ( way back in April )
"

On May 20, 2015, at 4:57 AM, Chitale, Hemant K <Hemant-K.Chitale_at_sc.com<mailto:Hemant-K.Chitale_at_sc.com>> wrote:

Anyone know what this Bug is :
Bug 20901134 : A ROW WITH 999 COLUMNS WILL NOT CAUSE 'ROW CHAINED' IN 12C

Thereís no text in the bug.

Hemant K Chitale
Senior Product Specialist
Finance&Risk Product Engineering

Standard Chartered Bank
7 Changi Business Park Crescent
Singapore 486028

Phone : +65-6596 3127
Email : Hemant-K.Chitale_at_sc.com<mailto:Hemant-K.Chitale_at_sc.com> Fonenet : 652-63127

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Received on Thu May 21 2015 - 08:48:16 CEST

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