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In pg_ctl, work around ERROR_SHARING_VIOLATION on the postmaster log file. 

On Windows, we use CMD.EXE to redirect the postmaster's stdout/stderr
into a log file.  CMD.EXE will open that file with non-sharing-friendly
parameters, and the file will remain open for a short time after the
postmaster has removed postmaster.pid.  This can result in an
ERROR_SHARING_VIOLATION failure if we attempt to start a new postmaster
immediately with the same log file (e.g. during "pg_ctl restart").
This seems to explain intermittent buildfarm failures we've been seeing
on Windows machines.

To fix, just open and close the log file using our own pgwin32_open(),
which will wait if necessary to avoid the failure.  (Perhaps someday
we should stop using CMD.EXE, but that would be a far more complex
patch, and it doesn't seem worth the trouble ... yet.)

Back-patch to v12.  This only solves the problem when frontend fopen()
is redirected to pgwin32_fopen(), which has only been true since commit
0ba06e0bf.  Hence, no point in back-patching further, unless we care
to back-patch that change too.

Diagnosis and patch by Alexander Lakhin (bug #16154).

Discussion: https://postgr.es/m/16154-1ccf0b537b24d5e0@postgresql.org
This commit is contained in:
Tom Lane 2019-12-10 13:17:08 -05:00
parent 5a20b0219e
commit 0da33c762b
1 changed files with 21 additions and 0 deletions
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21
src/bin/pg_ctl/pg_ctl.c
View File

@ -519,8 +519,29 @@ start_postmaster(void)
comspec = "CMD";
if (log_file != NULL)
{
/*
* First, touch the log file. The main value of this is that if the
* file is still locked by a previous postmaster run, we'll wait until
* it comes free, instead of failing with ERROR_SHARING_VIOLATION.
* (It'd be better to open the file in a sharing-friendly mode, but we
* can't use CMD.EXE to do that, so work around it. Note that the
* previous postmaster will still have the file open for a short time
* after removing postmaster.pid.)
*/
FILE *fd = fopen(log_file, "a");
if (fd == NULL)
{
write_stderr(_("%s: could not create log file \"%s\": %s\n"),
progname, log_file, strerror(errno));
exit(1);
}
fclose(fd);
snprintf(cmd, MAXPGPATH, "\"%s\" /C \"\"%s\" %s%s < \"%s\" >> \"%s\" 2>&1\"",
comspec, exec_path, pgdata_opt, post_opts, DEVNULL, log_file);
}
else
snprintf(cmd, MAXPGPATH, "\"%s\" /C \"\"%s\" %s%s < \"%s\" 2>&1\"",
comspec, exec_path, pgdata_opt, post_opts, DEVNULL);