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Before, BAS_BULKREAD was always of size 256kB. With the default io_combine_limit of 16, that only allowed 1-2 IOs to be in flight - insufficient even on very low latency storage. We don't just want to increase the size to a much larger hardcoded value, as very large rings (10s of MBs of of buffers), appear to have negative performance effects when reading in data that the OS has cached (but not when actually needing to do IO). To address this, increase the size of BAS_BULKREAD to allow for io_combine_limit * effective_io_concurrency buffers getting read in. To prevent the ring being much larger than useful, limit the increased size with GetPinLimit(). The formula outlined above keeps the ring size to sizes for which we have not observed performance regressions, unless very large effective_io_concurrency values are used together with large shared_buffers setting. Reviewed-by: Thomas Munro <thomas.munro@gmail.com> Discussion: https://postgr.es/m/lqwghabtu2ak4wknzycufqjm5ijnxhb4k73vzphlt2a3wsemcd@gtftg44kdim6 Discussion: https://postgr.es/m/uvrtrknj4kdytuboidbhwclo4gxhswwcpgadptsjvjqcluzmah@brqs62irg4dt
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/.