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Commit bbc1376b39 added a new lp_valid[]
array which records whether or not a line pointer was thought to be
valid, but entries could sometimes get set to true in cases where that
wasn't actually safe. Fix that.
Suppose A is a redirect line pointer and B is the other line pointer
to which it points. The old code could mishandle this situation in a
couple of different ways. First, if B was unused, we'd complain about
corruption but still set lp_valid[A] = true, causing later code
to try to access the B as if it were pointing to a tuple. Second,
if B was dead, we wouldn't complain about corruption at all, which is
an oversight, and would also set lp_valid[A] = true, which would
again confuse later code. Fix all that.
In the case where B is a redirect, the old code was correct, but
refactor things a bit anyway so that all of these cases are handled
more symmetrically. Also add an Assert() and some comments.
Andres Freund and Robert Haas
Discussion: http://postgr.es/m/20230323172607.y3lejpntjnuis5vv%40awork3.anarazel.de
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/.