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Until now, the -C option of postgres was handled before a small subset of GUCs computed at runtime are initialized, leading to incorrect results as GUC machinery would fall back to default values for such parameters. For example, data_checksums could report "off" for a cluster as the control file is not loaded yet. Or wal_segment_size would show a segment size at 16MB even if initdb --wal-segsize used something else. Worse, the command would fail to properly report the recently-introduced shared_memory, that requires to load shared_preload_libraries as these could ask for a chunk of shared memory. Support for runtime GUCs comes with a limitation, as the operation is now allowed on a running server. One notable reason for this is that _PG_init() functions of loadable libraries are called before all runtime-computed GUCs are initialized, and this is not guaranteed to be safe to do on running servers. For the case of shared_memory_size, where we want to know how much memory would be used without allocating it, this limitation is fine. Another case where this will help is for huge pages, with the introduction of a different GUC to evaluate the amount of huge pages required for a server before starting it, without having to allocate large chunks of memory. This feature is controlled with a new GUC flag, and four parameters are classified as runtime-computed as of this change: - data_checksums - shared_memory_size - data_directory_mode - wal_segment_size Some TAP tests are added to provide some coverage here, using data_checksums in the tests of pg_checksums. Per discussion with Andres Freund, Justin Pryzby, Magnus Hagander and more. Author: Nathan Bossart Discussion: https://postgr.es/m/F2772387-CE0F-46BF-B5F1-CC55516EB885@amazon.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: 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/.