Hi, On 03/26/2016 10:18 AM, Tatsuo Ishii wrote:

Fair point. Attached is v18 of the patch, after pgindent cleanup.## Advertising

Here are some feedbacks to v18 patch. 1) regarding examples in create_statistics manual Here are numbers I got. "with statistics" referrers to the case where multivariate statistics are used. "without statistics" referrers to the case where multivariate statistics are not used. The numbers denote estimated_rows/actual_rows. Thus closer to 1.0 is better. Some numbers are shown as a fraction to avoid 0 division. In my understanding case 1, 3, 4 showed that multivariate statistics superior. 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.`

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?`

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.`

regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers