5e89985928
Previously StrategyGetBuffer() acquired the buffer header spinlock for every buffer, whether it was reusable or not. If reusable, it'd be returned, with the lock held, to GetVictimBuffer(), which then would pin the buffer with PinBuffer_Locked(). That's somewhat violating the spirit of the guidelines for holding spinlocks (i.e. that they are only held for a few lines of consecutive code) and necessitates using PinBuffer_Locked(), which scales worse than PinBuffer() due to holding the spinlock. This alone makes it worth changing the code. However, the main reason to change this is that a future commit will make PinBuffer_Locked() slower (due to making UnlockBufHdr() slower), to gain scalability for the much more common case of pinning a pre-existing buffer. By pinning the buffer with a single atomic operation, iff the buffer is reusable, we avoid any potential regression for miss-heavy workloads. There strictly are fewer atomic operations for each potential buffer after this change. The price for this improvement is that freelist.c needs two CAS loops and needs to be able to set up the resource accounting for pinned buffers. The latter is achieved by exposing a new function for that purpose from bufmgr.c, that seems better than exposing the entire private refcount infrastructure. The improvement seems worth the complexity. Reviewed-by: Robert Haas <robertmhaas@gmail.com> Reviewed-by: Matthias van de Meent <boekewurm+postgres@gmail.com> Discussion: https://postgr.es/m/fvfmkr5kk4nyex56ejgxj3uzi63isfxovp2biecb4bspbjrze7@az2pljabhnff |
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| configure | ||
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| COPYRIGHT | ||
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| HISTORY | ||
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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.
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/.