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Alvaro Herrera 4482c6a23f BRIN revmap pages are not standard pages ...
... and therefore we ought not to tell XLogRegisterBuffer the opposite,
when writing XLog for a brin update that moves the index tuple to a
different page.  Otherwise, xlog insertion would try to "compress the
hole" when producing a full-page image for it; but since we don't update
pd_lower/upper, the hole covers the whole page.  On WAL replay, the
revmap page becomes empty and so the entire portion of the index is
useless and needs to be recomputed.

This is low-probability: a BRIN update only moves an index tuple to a
different page when the summary tuple is larger than the existing one,
which doesn't happen with fixed-width datatypes.  Also, the revmap
page must be first after a checkpoint.

Report and patch: Kuntal Ghosh
Bug is alleged to have detected by a WAL-consistency-checking tool.
Discussion: https://postgr.es/m/CAGz5QCJ=00UQjScSEFbV=0qO5ShTZB9WWz_Fm7+Wd83zPs9Geg@mail.gmail.com

I posted a test case demonstrating the problem, but I'm refraining from
adding it to the test suite; if the WAL consistency tool makes it in,
that will be a better way to catch this from regressing.  (We should
definitely have someting that causes not-same-page updates, though.)
2017-01-09 18:19:29 -03:00
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src BRIN revmap pages are not standard pages ... 2017-01-09 18:19:29 -03:00
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PostgreSQL Database Management System
=====================================

This directory contains the source code distribution of the PostgreSQL
database management system.

PostgreSQL is an advanced object-relational database management system
that supports an extended subset of the SQL standard, including
transactions, foreign keys, subqueries, triggers, user-defined types
and functions.  This distribution also contains C language bindings.

PostgreSQL has many language interfaces, many of which are listed here:

	http://www.postgresql.org/download

See the file INSTALL for instructions on how to build and install
PostgreSQL.  That file also lists supported operating systems and
hardware platforms and contains information regarding any other
software packages that are required to build or run the PostgreSQL
system.  Copyright and license information can be found in the
file COPYRIGHT.  A comprehensive documentation set is included in this
distribution; it can be read as described in the installation
instructions.

The latest version of this software may be obtained at
http://www.postgresql.org/download/.  For more information look at our
web site located at http://www.postgresql.org/.