Thread: Re: [GENERAL] Unable to get postgres running after long time no vacuum
"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
"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
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"
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
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.
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
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 allowancefor ignorance." (MichaelBrusser)