Sent from my BlackBerry - the most secure mobile device
Sent: August 9, 2017 14:52
Subject: Re: [PERFORM] Unlogged tables

Please don't top post.

On 8/9/2017 2:30 PM,<> 
> On 8/9/2017 2:17 PM,<> wrote:

>> On Wed, 9 Aug 2017 09:14:48 -0700, Jeff Janes 
>> <><> 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 

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.


Hello George... I know about not doing top posting but was emailing from my 
phone, and just recently moved to Android. I think I am still not configured 

Somewhat orthogonal, but any particular reason why top posts == bad, or just 

I will try a few scenarios and report back. I do not believe I have long cp 
intervals and I do not believe the windows machine shuts down faster than 

Finally, my true question was whether Postgres would support something like 
worm with the performance benefits of UNLOGGED, but not the inconveniences of 
auto truncates.


Reply via email to