"Leon Mergen" <leon@solatis.com> writes:
>> Perhaps you are not shutting down the standalone mode cleanly after
>> the vacuum?

> Okay, that was obviously it -- I didn't realize I needed to send a
> crtl+D signal to the server when in single user mode to shut it down,
> and figured that any uncommitted changes would be replayed when the
> database was started.

Most of them would be, but the one you actually needed here (the update
of pg_database.datfrozenxid) is treated as a non-WAL-logged action in
pre-8.2 releases :-( ... so you had to have a checkpoint to ensure it
got out to disk.

It's actually not that easy to get out of the single-user mode without
it doing a checkpoint. I suppose you must have either SIGQUIT or
SIGKILL'd it. While there's nothing we can do about SIGKILL, it strikes
me that it might be a good safety measure if single-user mode treated
SIGQUIT the same as SIGTERM, ie, non-panic shutdown. Comments anyone?

regards, tom lane

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"Leon Mergen" <leon@solatis.com> writes:
> On 7/8/07, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> It's actually not that easy to get out of the single-user mode without
>> it doing a checkpoint. I suppose you must have either SIGQUIT or
>> SIGKILL'd it. While there's nothing we can do about SIGKILL, it strikes
>> me that it might be a good safety measure if single-user mode treated
>> SIGQUIT the same as SIGTERM, ie, non-panic shutdown. Comments anyone?

> What I found with SIGTERM was that it did nothing, since it was still
> waiting for the (single-user) client to exit, and thus had no effect
> unless I sent an end-of-input ctrl+d singal, which would have resulted
> in a shutdown anyway.

We might need a bit of rejiggering around the edges of the single-user
command reading code to make this work nicely, but what I'm envisioning
is that a keyboard-generated SIGQUIT ought to result in a clean
shutdown, same as EOF does.

At least on my machine there doesn't seem to be a defined way to
generate SIGTERM from the terminal; so I can see where if someone hasn't
read the postgres man page carefully, their first instinct upon finding
that control-C doesn't get them out of single-user mode might be to type
control-\ (or whatever the local QUIT character is). It doesn't seem
like it should be quite that easy to force a panic stop.

regards, tom lane

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Tom Lane wrote:
> "Leon Mergen" <leon@solatis.com> writes:
> > On 7/8/07, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >> It's actually not that easy to get out of the single-user mode without
> >> it doing a checkpoint. I suppose you must have either SIGQUIT or
> >> SIGKILL'd it. While there's nothing we can do about SIGKILL, it strikes
> >> me that it might be a good safety measure if single-user mode treated
> >> SIGQUIT the same as SIGTERM, ie, non-panic shutdown. Comments anyone?
>
> > What I found with SIGTERM was that it did nothing, since it was still
> > waiting for the (single-user) client to exit, and thus had no effect
> > unless I sent an end-of-input ctrl+d singal, which would have resulted
> > in a shutdown anyway.
>
> We might need a bit of rejiggering around the edges of the single-user
> command reading code to make this work nicely, but what I'm envisioning
> is that a keyboard-generated SIGQUIT ought to result in a clean
> shutdown, same as EOF does.
>
> At least on my machine there doesn't seem to be a defined way to
> generate SIGTERM from the terminal; so I can see where if someone hasn't
> read the postgres man page carefully, their first instinct upon finding
> that control-C doesn't get them out of single-user mode might be to type
> control-\ (or whatever the local QUIT character is). It doesn't seem
> like it should be quite that easy to force a panic stop.

That seems reasonable, but I know an awful lot of people that don't know
how to generate SIGQUIT at all (I only learned about it about a year
ago, I think). In fact anyone who doesn't already know that Ctrl-D
closes the session is not very likely to know about Ctrl-\. So while we
should do it anyway, IMHO there's not much gain there. I think it may
be good to add "exit" and "quit" commands to close the standalone
session.

--
Alvaro Herrera Developer, http://www.PostgreSQL.org/
"God is real, unless declared as int"

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Alvaro Herrera <alvherre@commandprompt.com> writes:
> Tom Lane wrote:
>> At least on my machine there doesn't seem to be a defined way to
>> generate SIGTERM from the terminal; so I can see where if someone hasn't
>> read the postgres man page carefully, their first instinct upon finding
>> that control-C doesn't get them out of single-user mode might be to type
>> control-\ (or whatever the local QUIT character is). It doesn't seem
>> like it should be quite that easy to force a panic stop.

> That seems reasonable, but I know an awful lot of people that don't know
> how to generate SIGQUIT at all (I only learned about it about a year
> ago, I think). In fact anyone who doesn't already know that Ctrl-D
> closes the session is not very likely to know about Ctrl-\.

Sure, but those who do know how to SIGQUIT might reach for that before
they reach for control-D. There's hardly anyone out there who could
be called an experienced user of the standalone mode, I think, and so
we shouldn't assume that users always know control-D is the way out.

regards, tom lane

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Tom Lane wrote:
> Alvaro Herrera <alvherre@commandprompt.com> writes:
> > Tom Lane wrote:
> >> At least on my machine there doesn't seem to be a defined way to
> >> generate SIGTERM from the terminal; so I can see where if someone hasn't
> >> read the postgres man page carefully, their first instinct upon finding
> >> that control-C doesn't get them out of single-user mode might be to type
> >> control-\ (or whatever the local QUIT character is). It doesn't seem
> >> like it should be quite that easy to force a panic stop.
>
> > That seems reasonable, but I know an awful lot of people that don't know
> > how to generate SIGQUIT at all (I only learned about it about a year
> > ago, I think). In fact anyone who doesn't already know that Ctrl-D
> > closes the session is not very likely to know about Ctrl-\.
>
> Sure, but those who do know how to SIGQUIT might reach for that before
> they reach for control-D. There's hardly anyone out there who could
> be called an experienced user of the standalone mode, I think, and so
> we shouldn't assume that users always know control-D is the way out.

I agree completely, but is that an argument _against_ a "quit" command?
(Maybe the argument against the quit command is feature freeze.)

--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

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Alvaro Herrera <alvherre@commandprompt.com> writes:
> Tom Lane wrote:
>> Sure, but those who do know how to SIGQUIT might reach for that before
>> they reach for control-D. There's hardly anyone out there who could
>> be called an experienced user of the standalone mode, I think, and so
>> we shouldn't assume that users always know control-D is the way out.

> I agree completely, but is that an argument _against_ a "quit" command?

No, it's orthogonal to whether we want a "quit" command. (My opinion is
not, because what the heck will we do with it in multiuser mode? And
there is no good way to shoehorn it into just the single-user mode, it'd
have to be a grammar entry.)

regards, tom lane

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Tom Lane wrote:

> No, it's orthogonal to whether we want a "quit" command. (My opinion is
> not, because what the heck will we do with it in multiuser mode? And
> there is no good way to shoehorn it into just the single-user mode, it'd
> have to be a grammar entry.)

Hmm, I was thinking that we could just add it in its own grammar, but
then I remembered that the separate grammar is for the bootstrap mode,
not standalone :-( Sorry for the noise.

--
Alvaro Herrera http://www.flickr.com/photos/alvherre/
"Just treat us the way you want to be treated + some extra allowance
for ignorance." (Michael Brusser)

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