«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@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx> On Behalf
Of Laurentiu Oprea
Sent: Donnerstag, 18. März 2021 12:10
To: Chinar Aliyev <chinaraliyev@xxxxxxxxx>
Cc: Jonathan Lewis <jlewisoracle@xxxxxxxxx>; ORACLE-L (oracle-l@xxxxxxxxxxxxx)
<oracle-l@xxxxxxxxxxxxx>
Subject: Re: disable histogram usage at session / statement level
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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