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It can be useful for a hash function to expose separate initialization, accumulation, and finalization steps. In particular, this is useful for building inline hash functions for simplehash. Instead of trying to whack around hash_bytes while maintaining its current behavior on all platforms, we base this work on fasthash (MIT licensed) which is simple, faster than hash_bytes for inputs over 12 bytes long, and also passes the hash function testing suite SMHasher. The fasthash functions have been reimplemented using our added-on incremental interface to validate that this method will still give the same answer, provided we have the input length ahead of time. This functionality lives in a new header hashfn_unstable.h. The name implies we have the freedom to change things across versions that would be unacceptable for our other hash functions that are used for e.g. hash indexes and hash partitioning. As such, these should only be used for in-memory data structures like hash tables. There is also no guarantee of being independent of endianness or pointer size. As demonstration, use fasthash for pgstat_hash_hash_key. Previously this called the 32-bit murmur finalizer on the three elements, then joined them with hash_combine(). The new function is simpler, faster and takes up less binary space. While the collision and bias behavior were almost certainly fine with the previous coding, now we have objective confidence of that. There are other places that could benefit from this, but that is left for future work. Reviewed by Jeff Davis, Heikki Linnakangas, Jian He, Junwang Zhao Credit to Andres Freund for the idea Discussion: https://postgr.es/m/20231122223432.lywt4yz2bn7tlp27%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. Copyright and license information can be found in the file COPYRIGHT. General documentation about this version of PostgreSQL can be found at: https://www.postgresql.org/docs/devel/ In particular, information about building PostgreSQL from the source code can be found at: https://www.postgresql.org/docs/devel/installation.html The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.