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Date: Thu, 17 Jul 2014 14:19:39 -0400
Subject: Re: Blocked thread
From: Larry Martell <larry.martell@gmail.com>
To: Chris Angelico <rosuav@gmail.com>
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On Thu, Jul 17, 2014 at 2:09 PM, Chris Angelico <rosuav@gmail.com> wrote:
> On Fri, Jul 18, 2014 at 4:03 AM, Larry Martell <larry.martell@gmail.com> wrote:
>> On Thu, Jul 17, 2014 at 2:01 PM, Chris Angelico <rosuav@gmail.com> wrote:
>>> On Fri, Jul 18, 2014 at 3:55 AM, Larry Martell <larry.martell@gmail.com> wrote:
>>>> I can have as many connections to the db server as I want, that's not
>>>> the issue. The issue is that my main thread seems to be blocked in the
>>>> join(), so I guess I'm going to need a separate script. I was trying
>>>> to avoid that.
>>>
>>> Right, but what you're trying to do is monitor the local thread, by
>>> spinning off a thread to do the deletion and then keeping an eye on it
>>> by attempting a timed join. I'm saying it'd probably be easier to do
>>> the monitoring on the server end, via a second connection. (It most
>>> likely doesn't need special database privileges, even; at least in
>>> PostgreSQL, any user can see pg_stat_activity entries for the same
>>> user.) That's usually going to be more reliable, plus the server can
>>> tell you whether the deletion is blocked waiting for a lock or busy
>>> writing to the disk or something else.
>>
>> Yes, I agree, but the second connection will have to be in a second
>> script, not the main thread of the script I have.
>
> Maybe. I don't know what facilities Oracle gives you; it might be
> possible to start a query asynchronously, with either a callback when
> it's done or a poll for completion. Then another connection could be
> used to keep an eye on the first one. But yes, doing it with a
> completely separate script would be simpler in many ways. Or you might
> be able to do the job with two threads.

I do not think Oracle support async or non-blocking queries as
Postgres does. But what I think I can do is not call join(), and just
start monitoring the server when I kick off the thread with the mail
sql it in.