pgsql: Avoid having vacuum set reltuples to 0 on non-empty relations in

On Thu, Mar 16, 2017 at 6:39 PM, Andrew Gierth
<rhodiumtoad@postgresql.org> wrote:

Avoid having vacuum set reltuples to 0 on non-empty relations in the
presence of page pins, which leads to serious estimation errors in the
planner. This particularly affects small heavily-accessed tables,
especially where locking (e.g. from FK constraints) forces frequent
vacuums for mxid cleanup.

Fix by keeping separate track of pages whose live tuples were actually
counted vs. pages that were only scanned for freezing purposes. Thus,
reltuples can only be set to 0 if all pages of the relation were
actually counted.

Backpatch to all supported versions.

Per bug #14057 from Nicolas Baccelli, analyzed by me.

Discussion: /messages/by-id/20160331103739.8956.94469@wrigleys.postgresql.org

In the department of nitpicks, we usually try to write commit messages
so that the first line is a summary line which stands alone, and then
there's a blank line, and then more follows. a la
https://chris.beams.io/posts/git-commit/#separate

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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On 03/17/2017 09:30 AM, Robert Haas wrote:

In the department of nitpicks, we usually try to write commit messages
so that the first line is a summary line which stands alone, and then
there's a blank line, and then more follows. a la
https://chris.beams.io/posts/git-commit/#separate

Yeah, In our case email subjects seem to be truncated at 64 chars, so
it's best to stay under that limit if possible - 50 chars is sometimes
pretty limiting.

cheers

andrew

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Andrew Dunstan https://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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Andrew Dunstan <andrew.dunstan@2ndquadrant.com> writes:

On 03/17/2017 09:30 AM, Robert Haas wrote:

In the department of nitpicks, we usually try to write commit messages
so that the first line is a summary line which stands alone, and then
there's a blank line, and then more follows. a la
https://chris.beams.io/posts/git-commit/#separate

Yeah, In our case email subjects seem to be truncated at 64 chars, so
it's best to stay under that limit if possible - 50 chars is sometimes
pretty limiting.

FWIW, I usually try to keep line length in commit messages to <= 75
characters, as that is the wrap boundary in "git log" output. It's
nice if the summary line can be made shorter, but it's often damn
hard to cram an adequate summary into 75 chars, let alone fewer.

(Links to mailing-list threads must ignore the length limit, sadly.)

regards, tom lane

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On Fri, Mar 17, 2017 at 10:00:17AM -0400, Tom Lane wrote:

Andrew Dunstan <andrew.dunstan@2ndquadrant.com> writes:

On 03/17/2017 09:30 AM, Robert Haas wrote:

In the department of nitpicks, we usually try to write commit messages
so that the first line is a summary line which stands alone, and then
there's a blank line, and then more follows. a la
https://chris.beams.io/posts/git-commit/#separate

Yeah, In our case email subjects seem to be truncated at 64 chars, so
it's best to stay under that limit if possible - 50 chars is sometimes
pretty limiting.

FWIW, I usually try to keep line length in commit messages to <= 75
characters, as that is the wrap boundary in "git log" output. It's
nice if the summary line can be made shorter, but it's often damn
hard to cram an adequate summary into 75 chars, let alone fewer.

(Links to mailing-list threads must ignore the length limit, sadly.)

Here are the length limits I have found, and I display this in my email
editor when I am creating a commit message:

-- email subject limit -----------------------------------------
-- gitweb summary limit --------------------------

--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +

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