RE: disable histogram usage at session / statement level
Date: Thu, 18 Mar 2021 11:20:11 +0000
Message-ID: <16972fca64c24025b94e1432fdb953c1_at_vontobel.com>
«I`m starting to think that actually the best method is to have them disabled since the beginning and where is the case create one. (instead of taking Maria`s advise to use auto and evaluate where they create issues) - not to mention that because of histograms for some tables the incremental stats don't work as expected “
Disabling histograms at the outset and then enabling them explicitly as needed might actually work well.
METHOD_OPT AUTO defeats the purpose of incremental stats, as synopses have to be recreated whenever the statistic gather procedure decides to create new histograms: https://nenadnoveljic.com/blog/incremental-statistics-histogram-pitfall/
Best regards,
Nenad
From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> On Behalf Of Laurentiu Oprea
Sent: Donnerstag, 18. März 2021 12:10
Thanks a lot, yes both methods work fine .
As a background for my question: I noticed that for a lot of tables the stats job computed hybrid histograms on ID or PARENT_ID columns and the cardinality estimate for joins using these columns are orders of magnitude trillion of rows. Dropping/disabling the histogram resolves the estimate to 20-30 millions (the expected cardinality)
Because there are so many tables I need to take now query by query and do a quick evaluation with/without histograms and drop where I see a negative impact.
I`m starting to think that actually the best method is to have them disabled since the beginning and where is the case create one. (instead of taking Maria`s advise to use auto and evaluate where they create issues) - not to mention that because of histograms for some tables the incremental stats don't work as expected
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To: Chinar Aliyev <chinaraliyev_at_gmail.com>
Cc: Jonathan Lewis <jlewisoracle_at_gmail.com>; ORACLE-L (oracle-l_at_freelists.org) <oracle-l_at_freelists.org>
Subject: Re: disable histogram usage at session / statement level
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Received on Thu Mar 18 2021 - 12:20:11 CET