On Wed, Sep 7, 2011 at 11:53 PM, Robert Treat <r...@xzilla.net> wrote: > On Tue, Sep 6, 2011 at 10:11 PM, Fujii Masao <masao.fu...@gmail.com> wrote: >> I agree that basically archive_command should not overwrite an existing file. >> But if the size of existing file is less than 16MB, it should do that. >> Otherwise, >> that WAL file would be lost forever. > > I think best practice in this case is that if you ever find an > existing file with the same name already in place, you should error > and investigate. We don't ship around partially completed WAL files, > and finding an existing one probably means something went wrong. (Of > course, we use rsync instead of copy/move, so we have some better > guarantees about this).
That's an option. But I don't think that finding an existing file is so serious problem. The most common cases which cause a partially-filled archived file are; 1. The server crashes while WAL file is being archived, and then the server restarts. In this case, the restarted server would find partially-filled archived file. 2. In replication environment, the master crashes while WAL file is being archived, and then a failover happens. In this case, new master would find partially-filled archived file. In these cases, I don't think it's so unsafe to overwrite an existing file. OTOH, the practice you explained might fill up an archive area and pg_xlog directory and then cause a PANIC error. Such a PANIC error is more serious thing at least for me. So I'd like to overwrite an exiting file when its size is not 16MB. >> I have another feature request; >> (5) Maybe not in the initial version, but eventually it might be >> nice to support calling posix_fadvise(POSIX_FADV_DONTNEED) >> after copying a WAL file. >> > > Can you go into more details on how you envision this working. I'm > mostly curious because I think rsync might already support this, which > would make it easy to incorporate. I'm expecting that the executable is written in C, it calls posix_fadvice against the file descriptor created when opening the WAL file in pg_xlog directory, just before closing that descriptor. Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers