Re: pgsql: Remove the restriction that the relmap must be 512 bytes.

On Wed, Jul 27, 2022 at 5:01 PM Thomas Munro <thomas.munro@gmail.com> wrote:
> On Wed, Jul 27, 2022 at 4:35 PM Michael Paquier <michael@paquier.xyz> wrote:
> > On Tue, Jul 26, 2022 at 07:10:22PM +0000, Robert Haas wrote:
> > > Remove the restriction that the relmap must be 512 bytes.
>
> > The CI on Windows is blowing up here and there after something that
> > looks to come from this commit, as of this backtrace:
> > 00000000`007fe300 00000001`405c62dd     postgres!errfinish(
> > char * filename = 0x00000001`40bf1513 "fd.c",
> > int lineno = 0n756,
> > char * funcname = 0x00000001`40bf14e0 "durable_rename")+0x41b
> > [c:\cirrus\src\backend\utils\error\elog.c @ 683]
>
> And here's what the error looks like:
>
> 2022-07-26 19:38:04.321 GMT [8020][client backend]
> [pg_regress/vacuum][8/349:4527] PANIC:  could not rename file
> "global/pg_filenode.map.tmp" to "global/pg_filenode.map": Permission
> denied
>
> Someone else still has the old file open, so we can't rename the new
> one to its name?  On Windows that should have gone through pgrename()
> in dirmod.c, which would retry 100 times with a 100ms sleep between.
> Since every backend reads that file (I added an elog() and saw it 2289
> times during make check), I guess you can run out of luck.
>
> /me thinks

Maybe we just have to rearrange the locking slightly?  Something like
the attached.