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Previously, these index types left the pd_lower field set to the default SizeOfPageHeaderData, which is really a lie because it ought to point past whatever space is being used for metadata. The coding accidentally failed to fail because we never told xlog.c that the metapage is of standard format --- but that's not very good, because it impedes WAL consistency checking, and in some cases prevents compression of full-page images. To fix, ensure that we set pd_lower correctly, not only when creating a metapage but whenever we write it out (these apparently redundant steps are needed to cope with pg_upgrade'd indexes that don't yet contain the right value). This allows telling xlog.c that the page is of standard format. The WAL consistency check mask functions are made to mask only if pd_lower appears valid, which I think is likely unnecessary complication, since any metapage appearing in a v11 WAL stream should contain valid pd_lower. But it doesn't cost much to be paranoid. Amit Langote, reviewed by Michael Paquier and Amit Kapila Discussion: https://postgr.es/m/0d273805-0e9e-ec1a-cb84-d4da400b8f85@lab.ntt.co.jp
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/.