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210622c60e
Break ReadBuffer() up into two steps. StartReadBuffers() and WaitReadBuffers() give us two main advantages: 1. Multiple consecutive blocks can be read with one system call. 2. Advice (hints of future reads) can optionally be issued to the kernel ahead of time. The traditional ReadBuffer() function is now implemented in terms of those functions, to avoid duplication. A new GUC io_combine_limit is defined, and the functions for limiting per-backend pin counts are made into public APIs. Those are provided for use by callers of StartReadBuffers(), when deciding how many buffers to read at once. The following commit will add a higher level mechanism for doing that automatically with a practical interface. With some more infrastructure in later work, StartReadBuffers() could be extended to start real asynchronous I/O instead of just issuing advice and leaving WaitReadBuffers() to do the work synchronously. Author: Thomas Munro <thomas.munro@gmail.com> Author: Andres Freund <andres@anarazel.de> (some optimization tweaks) Reviewed-by: Melanie Plageman <melanieplageman@gmail.com> Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi> Reviewed-by: Nazir Bilal Yavuz <byavuz81@gmail.com> Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com> Reviewed-by: Andres Freund <andres@anarazel.de> Tested-by: Tomas Vondra <tomas.vondra@enterprisedb.com> Discussion: https://postgr.es/m/CA+hUKGJkOiOCa+mag4BF+zHo7qo=o9CFheB8=g6uT5TUm2gkvA@mail.gmail.com