Horton

Re: pg_preadv() and pg_pwritev()

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Sergey Shinderuk <s.shinderuk@postgrespro.ru>
Cc: Thomas Munro <thomas.munro@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2021-01-13T16:13:15Z
Lists: pgsql-hackers 
Sergey Shinderuk <s.shinderuk@postgrespro.ru> writes:
> On 13.01.2021 12:56, Thomas Munro wrote:
>> On Wed, Jan 13, 2021 at 10:40 PM Sergey Shinderuk
>> <s.shinderuk@postgrespro.ru> wrote:
>>> note: 'pwritev' has been marked as being introduced in macOS 11.0 here,
>>> but the deployment target is macOS 10.15.0

>> Hrm...  So why did "configure" think you have pwritev, then?  It seems
>> like you must have been using different compilers or options at
>> configure time and compile time, no?

> No, i've just rerun configure from clean checkout without any options. 
> It does think that pwritev is available. I'll try to figure this out 
> later and come back to you. Thanks.

The symptoms sound consistent with using bleeding-edge Xcode on a
Catalina machine ... please report exact OS and Xcode versions.

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.

			regards, tom lane

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().