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Tom Lane authored
vac_truncate_clog() uses its own transaction ID as the comparison point in
a sanity check that no database's datfrozenxid has already wrapped around
"into the future".  That was probably fine when written, but in a lazy
vacuum we won't have assigned an XID, so calling GetCurrentTransactionId()
causes an XID to be assigned when otherwise one would not be.  Most of the
time that's not a big problem ... but if we are hard up against the
wraparound limit, consuming XIDs during antiwraparound vacuums is a very
bad thing.

Instead, use ReadNewTransactionId(), which not only avoids this problem
but is in itself a better comparison point to test whether wraparound
has already occurred.

Report and patch by Alexander Korotkov.  Back-patch to all versions.

Report: <CAPpHfdspOkmiQsxh-UZw2chM6dRMwXAJGEmmbmqYR=yvM7-s6A@mail.gmail.com>
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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/.