Re: Query Performance with params

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Mon, 1 May 2017 14:36:32 +0000
Message-ID: <MMXP123MB10377DC6D6B4B36C7C297BFAA5140_at_MMXP123MB1037.GBRP123.PROD.OUTLOOK.COM>

Mladen,

Larger histograms -- uses the same 254 columns by default New calculation for clustering_factor -- uses the old mechanism (table_cached_blocks = 1) by default

New type of histograms: you still get Top-N and Hybrid histograms with OFE= 11.2.0.4 if you have preference approximate_ndv = true (though you can disable them). But Frequency and Top-N give you much better accuracy virtually free of ANY cost (in 12.1.0.2) and Hybrid give you better accuracy for no increase over the 11g cost - the main problem is that frequency and top-N histograms may be based on a small sample size if you set OFE=11.2.0.4

Regards
Jonathan Lewis

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From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> on behalf of Mladen Gogala <gogala.mladen_at_gmail.com> Sent: 01 May 2017 13:22
To: Stefan Koehler
Cc: oracle-l_at_freelists.org
Subject: Re: Query Performance with params

Well, there are several more changes you didn't mention: new type of histograms, much larger histograms and a new way to calculate clustering factor.

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Received on Mon May 01 2017 - 16:36:32 CEST