Re: Unlogged tables

George Neuner <gneuner2@xxxxxxxxxxx> · Wed, 9 Aug 2017 15:52:26 -0400



    Please don't top post.

    
    On 8/9/2017 2:30 PM,
      ldh@xxxxxxxxxxxxxxxxxx wrote:

    
        > On 8/9/2017 2:17
          PM, gneuner2@xxxxxxxxxxx wrote:
      
      
                >> On Wed, 9 Aug 2017
                  09:14:48 -0700, Jeff Janes
                  <jeff.janes@xxxxxxxxx> wrote:

                  
                  >> Why doesn't the Windows scheduled shutdown
                  signal postgres to shutdown

                  >> cleanly and wait for it to do so?  That is
                  what is supposed to happen.

                  
                  > Windows *does* signal shutdown (and sleep and
                  hibernate and wakeup).  

                  > pg_ctl can catch these signals only when running
                  as a service ... it 

                  > will not catch any system signals when run as an
                  application.

                  
            Ok, I am not sure. I run Postgres as a service, and when my
            Windows rebooted after a patch, UNLOGGED tables were
            cleaned... maybe the patch process in Windows messed
            something up, I don't know.
        
      
    Hmm.  Do you have checkpoint intervals set very long?  Or do you
    have the Windows shutdown delay(s) set short?

    
    Data in unlogged tables persists only AFTER a checkpoint ... if the
    tables had been written to and were "dirty", and the system went
    down before the shutdown checkpoint (or before the shutdown
    checkpoint completed), then the tables would be truncated at the
    next startup.  

    
    Service control in Windows is very different from Unix/Linux, and
    Windows is not completely POSIX compatible.  I develop software for
    Windows and Linux, but I only use Postgresql.  Postgresql was
    written originally for Unix and it is possible that the Windows
    version is not doing something quite right.

    
    I took a quick glance at the source for pg_ctl: 
    SERVICE_CONTROL_SHUTDOWN and SERVICE_CONTROL_STOP both just set an
    shared event to notify the writer processes to terminate.  Offhand I
    don't see where pg_ctl - running as a service - is waiting for the
    writer processes to actually terminate ( it does wait if run from
    the command line ).   It's possible that your system shut down too
    quickly and the WAL writer was killed instead of terminating
    cleanly.

    
    Just FYI, re: Postgresql as a user application.  

    
    Windows doesn't send *signals* (ala Unix) at all ... it is message
    based.  The control messages are different for applications and
    services - e.g., WM_SHUTDOWN is sent to applications,
    SERVICE_CONTROL_SHUTDOWN is sent to services.  In order for an
    application to catch a message, it must create a window.  

    
    pg_ctl is a command line program which does not create any windows
    (in any mode).  It was designed to enable it to run as a service,
    but when run as a user application it will can't receive any system
    messages.  The user *must* manually stop a running database cluster
    before shutting down or sleeping.

    
    George