Use pg_pread() and pg_pwrite() for data files and WAL.
Cut down on system calls by doing random I/O using offset-based OS
routines where available. Remove the code for tracking the 'virtual'
seek position. The only reason left to call FileSeek() was to get
the file's size, so provide a new function FileSize() instead.
Author: Oskari Saarenmaa, Thomas Munro
Reviewed-by: Thomas Munro, Jesper Pedersen, Tom Lane, Alvaro Herrera
Discussion: https://postgr.es/m/CAEepm=02rapCpPR3ZGF2vW=SBHSdFYO_bz_f-wwWJonmA3APgw@mail.gmail.com
Discussion: https://postgr.es/m/
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Discussion: https://postgr.es/m/
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