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Commit 4d0e994eed added support for partial TOAST decompression, so the decompression is interrupted after producing the requested prefix. For prefix and slices near the beginning of the entry, this may saves a lot of decompression work. That however only deals with decompression - the whole compressed entry was still fetched and re-assembled, even though the compression used only a small fraction of it. This commit improves that by computing how much compressed data may be needed to decompress the requested prefix, and then fetches only the necessary part. We always need to fetch a bit more compressed data than the requested (uncompressed) prefix, because the prefix may not be compressible at all and pglz itself adds a bit of overhead. That means this optimization is most effective when the requested prefix is much smaller than the whole compressed entry. Author: Binguo Bao Reviewed-by: Andrey Borodin, Tomas Vondra, Paul Ramsey Discussion: https://www.postgresql.org/message-id/flat/CAL-OGkthU9Gs7TZchf5OWaL-Gsi=hXqufTxKv9qpNG73d5na_g@mail.gmail.com
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/.