Horton

Re: pg_preadv() and pg_pwritev()

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Sergey Shinderuk <s.shinderuk@postgrespro.ru>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2021-01-13T19:52:04Z
Lists: pgsql-hackers

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On Thu, Jan 14, 2021 at 5:13 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I have a different complaint, using Big Sur and Xcode 12.3:
>
> /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib: file: libpgport.a(pread.o) has no symbols
> /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib: file: libpgport_shlib.a(pread_shlib.o) has no symbols
> /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib: file: libpgport_srv.a(pread_srv.o) has no symbols
>
> Looks like we need to be more careful about not including pread.c
> in the build unless it actually has code to contribute.

I did it that way because it made it easy to test different
combinations of the replacements on computers that do actually have
pwrite and pwritev, just by tweaking pg_config.h.  Here's an attempt
to do it with AC_REPLACE_FUNCS, which avoids creating empty .o files.
It means that to test the replacements on modern systems you have to
tweak pg_config.h and also add the relevant .o files to LIBOBJS in
src/Makefile.global, but that seems OK.

Commits

  1. Improve our heuristic for selecting PG_SYSROOT on macOS.

  2. Move our p{read,write}v replacements into their own files.

  3. Don't use elog() in src/port/pwrite.c.

  4. Use vectored I/O to fill new WAL segments.

  5. Provide pg_preadv() and pg_pwritev().