Re: multivariate statistics v14

>> 	with statistics	without statistics
>> case1	0.98		0.01
>> case2	98/0		1/0
> 
> The case2 shows that functional dependencies assume that the
> conditions used in queries won't be incompatible - that's something
> this type of statistics can't fix.

It would be nice if that's mentioned in the manual to avoid user's
confusion.

>> case3	1.05		0.01
>> case4	1/0		103/0
>> case5	18.50		18.33
>> case6	111123/0	1111123/0
> 
> The last two lines (case5 + case6) seem a bit suspicious. I believe
> those are for the histogram data, and I do get these numbers:
> 
> case5    0.93 (5517 / 5949)         42.0 (249943 / 5949)
> case6    100/0                      100/0
> 
> Perhaps you've been using the version before the bugfix, with ANALYZE
> on the wrong table?

You are right. I accidentally ANALYZE t2, not t3. Now I get these
numbers:

case5    1.23 (7367 / 5968)         41.7 (249118 / 5981)
case6    117/0                      162092/0

>> 2) following comments by me are not addressed in the v18 patch.
>>
>>> - There's no docs for pg_mv_statistic (should be added to "49. System
>>>   Catalogs")
>>>
>>> - The word "multivariate statistics" or something like that should
>>>   appear in the index.
>>>
>>> - There are some explanation how to deal with multivariate statistics
>>>   in "14.1 Using Explain" and "14.2 Statistics used by the Planner"
>>>   section.
> 
> Yes, those are valid omissions. I plan to address them, and I'd also
> considering adding a section to 65.1 (How the Planner Uses
> Statistics), explaining more thoroughly how the planner uses
> multivariate stats.

Great.

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp