Re: Kludge in pg_standby.c - Mailing list pgsql-hackers

I have moved this to the next commit-fest.

---------------------------------------------------------------------------

Gregory Stark wrote:
> 
> There's a suspicious ifdef in pg_standby for WIN32 which smells like a kludge
> added to work around a Windows problem which makes it work but at great
> expense:
> 
> #ifdef WIN32
>                 /*
>                  * Windows reports that the file has the right number of bytes
>                  * even though the file is still being copied and cannot be
>                  * opened by pg_standby yet. So we wait for sleeptime secs
>                  * before attempting to restore. If that is not enough, we
>                  * will rely on the retry/holdoff mechanism.
>                  */
>                 pg_usleep(sleeptime * 1000000L);
> #endif
> 
> This happens before we return *any* WAL file to be processed. That means it
> slows down the processing of any file by 1s. On a server which has fallen
> behind this means it can't process files as quickly as it can copy them, it's
> limited to at most 1/s.
> 
> I think it wouldn't be hard to do this properly. We can try to open the file,
> handle the expected Windows error by sleeping for 1s and repeating until we
> can successfully open it. Something like (untested):
> 
>         bool success = false;
>                 int fd, tries = 10;
>         while (--tries) {
>                    fd = open(WALFilePath, O_RDONLY);
>                    if (fd >= 0) {
>                        close(fd);
>                        success = true;
>                        break;
>                    } else if (errno == EWINDOWSBLOWS) {
>                        usleep(1000000);
>                    } else {
>                        perror("pg_standby open:");
>                        exit(2);
>                    }
>                }
>                if (!success) {
>                    fprintf(stderr, "pg_standby: couldn't open file \"%s\" due to \"%s\", 
>                            WALFilePath, strerror(EWINDOWSBLOWS));
>                    exit(2);
>                }
> 
> 
> -- 
>   Gregory Stark
>   EnterpriseDB          http://www.enterprisedb.com
>   Ask me about EnterpriseDB's RemoteDBA services!
> 
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