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Re: Why PG uses nested-loop join when no indexes are available? - Mailing list pgsql-general

From David Grelaud
Subject Re: Why PG uses nested-loop join when no indexes are available?
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Msg-id CABKm3pggjf_Bo7hd9nvG3SwizXcynE+0ANFfp54GYrOQQYCzyQ@mail.gmail.com
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In response to Re: Why PG uses nested-loop join when no indexes are available?  (Tom Lane <tgl@sss.pgh.pa.us>)
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Thank you for your fast response!

I'm sorry, my vocabulary may be not correct and my "french approach" to explain my problem is not efficient ;).

But the underestimation problem in complex queries is still there? ... and generates potential "dangerous" plans (nested loop).

We thought at the beginning we were alone but it seems to be a problem of most database systems.
What do you think about the paragraph 4.1 of this paper  http://www.vldb.org/pvldb/vol9/p204-leis.pdf ?

Regards,
-------------------
David Grelaud,
Ideolys.



2016-01-13 16:02 GMT+01:00 Tom Lane <tgl@sss.pgh.pa.us>:
David Grelaud <dgrelaud@ideolys.com> writes:
> Statistics are not propagated when Common Table Expressions (CTE) are used.
> The cardinality of a CTE is equal to 1 most of the time

Really?

The rest of this seems to be proceeding from completely false assumptions.

                        regards, tom lane

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