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Re: Thread manager

From: Guillaume Lelarge <guillaume(at)lelarge(dot)info>
To: Magnus Hagander <magnus(at)hagander(dot)net>
Cc: Dave Page <dpage(at)pgadmin(dot)org>, pgadmin-hackers <pgadmin-hackers(at)postgresql(dot)org>
Subject: Re: Thread manager
Date: 2011-10-10 19:27:47
Message-ID: 1f12729d48846283fac6040a2f5c65be@localhost (view raw or flat)
Thread:
Lists: pgadmin-hackers
On Mon, 10 Oct 2011 20:45:13 +0200, Magnus Hagander <magnus(at)hagander(dot)net>
wrote:
> On Mon, Oct 10, 2011 at 12:06, Dave Page <dpage(at)pgadmin(dot)org> wrote:
>> On Sun, Oct 9, 2011 at 9:22 AM, Guillaume Lelarge
>> <guillaume(at)lelarge(dot)info> wrote:
>>>
>>>> > worse with Vladimir's patch as there is no UI at all to show the
>>>> > progress on the copy (if you copy more than one table of course).
>>>>
>>>> There needs to be some status indication, even if it's just an
>>>> animation (maybe busy cursor over the dialogue) and text that says
>>>> "Copying table 1...",  "Copying table 2..." etc.
>>>>
>>>
>>> AFAICT, you only have the final status.
>>
>> Some progress text would certainly be sensible - this sort of
>> operation could take hours.
>>
>>>> > I was a few weeks ago at a customer's office, and he showed me a
>>>> > nice UI
>>>> > of a tool (unfortunately, I don't remember its name) that allowed
>>>> > him to
>>>> > queue some jobs. So I wondered if we could do the same. When you're
>>>> > in
>>>> > the VACUUM dialog, and click OK, it adds a job in the jobs list,
and
>>>> > a
>>>> > thread will catch it as soon as it is available for a new job. The
UI
>>>>
>>>> We don't need to use a thread pool to save resources for this kind of
>>>> thing, even if running on a net book - we can just launch a thread as
>>>> needed and let the OS deal with resource management. I can't imagine
>>>> the user will be able to start enough task threads that even a
Windows
>>>> 95 system couldn't cope.
>>>>
>>>
>>> I'm not talking about performance. I'm talking about UI. I'm talking
>>> about adding a single UI to handle many operations.
>>
>> You were talking about a thread pool, which I think is totally
>> unnecessary: "a thread will catch it as soon as it is available for a
>> new job"
> 
> Not sure that necessarily indicates a threadpool, but let's not get
> hung up on details :-) FWIW, I think a threadpool would be very much
> overkill as well - not to mention that they'd all require separate db
> connections anyway, so you'd have to have all sorts of ways to limit
> it etc..
> 

No, I don't want a threadpool. Maybe a timer to check if a new appeared,
and maybe one thread to launch a job.

>>>> > could be as simple as a new pane in frmMain, with a listbox which
>>>> > contains the list of job, and their status.
>>>>
>>>> All of these threads that we have at the moment are returning data to
>>>> the UI for display (in theory, as work progresses, but I'm aware that
>>>> doesn't work everywhere). Are you suggesting that we would get rid of
>>>> that UI, and make the user move to another window, display the
>>>> appropriate pane (something like this wouldn't be visible by
default),
>>>> and then double-click the appropriate row to view the output? What
>>>> about purging old data? How would we decide when to remove something
>>>> from the list?
>>>>
>>>
>>> Let's say you want to do a "VACUUM FULL" (yeah, I know, crazy idea).
>>> Now, you'll have the Maintenance window working, and you can get to
the
>>> browser window to continue (if you can) your work.
>>
>> If you can't, then we have a bug in the current code. You should be
>> able to minimise the Maintenance window and carry on.
> 
> Can you have multiple maintenance windows open at the same time, all
> minimized?
> 

As many as you want...
 
>>> What I suggest is adding a pane in the browser window. So, you open
the
>>> Maintenance window, do your stuff to launch a VACUUM FULL. Then, the
>>> Maintenance window is closed, the "Jobs" pane is opened (if it wasn't
>>> already), a new job appears stating that it is a VACUUM FULL job on
>>> database/table whatever, and that the job is running. We can probably
>>> add more infomations (for example, the duration, if it's blocked by
>>> another session, etc.) and more actions (kill it, pause it, resume
it).
>>
>> Yeah, I understand what you're proposing. I've seen similar things in
>> other products in years gone by. I don't think there's any need for us
>> to do anything like that though - I think it would take a lot of
>> engineering and buy little. More importantly, I think it will be
>> detrimental to the user experience, as a task that was once confined
>> to one dialogue now is started from one, and ends on separate window.
> 
> I'd find it useful, actually. But even more so if there was one
> "execute now" and one "execute in the background" button, or something
> like that. Being able to sticka bunch of things in a queue, knowing
> they execute one by one over a single connection so I don't overload
> the server, would be useful. (Which makes it even more important that
> it's not a threadpool, really :D)

+1

I suppose I'll work on it sometime, just to get a POC, something to show.
Right now, I have something else to do :)


-- 
Guillaume
 http://www.postgresql.fr
 http://dalibo.com

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