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070e21268b
SnapBuildInitialSnapshot() converts the snapshot builder's list of
committed transactions into a regular MVCC snapshot, which is then used
with HeapTupleSatisfiesMVCC(). However, a snapshot produced that way
and used as an MVCC snapshot can potentially cause data corruption, if
it captures a transaction after it writes its commit WAL record but
before it has updated its CLOG entry: it will be incorrectly used to set
hint bits as if that transaction had aborted.
Fix by having SnapBuildInitialSnapshot() wait until such transactions
have removed themselves from procarray, which guarantees correct
visibility.
Other uses of SnapBuildBuildSnapshot only use the snapshot as
historical, so they don't need the waits, but add commentary in that
function to alert possible future callers.
While at this, backpatch commit 504fe10d1d, "Fix misplaced comment in
snapbuild.c." The comment it moved was nearby the place we modify.
This bug was diagnosed by stress-testing of REPACK (CONCURRENTLY) in
branch 19, so add a test case that tickles it using that feature in that
branch and master. However, the bug exists in all branches, and in
branch 18 we can add a test with regular logical decoding using
injection points that tickles it. Unfortunately that test cannot be
backpatched to earlier branches for lack of facilities.
Reported-by: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
Author: Antonin Houska <ah@cybertec.at>
Author: Rui Zhao <zhaorui126@gmail.com>
Backpatch-through: 14
Discussion: https://postgr.es/m/85833.1768840165@localhost
Discussion: https://postgr.es/m/CADzfLwU78as45To9a%3D-Qkr5jEg3tMxc5rUtdKy2MTv4r_SDGng%40mail.gmail.com
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: https://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 https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.