this was treat man .. cool and imaginative for sure!!
- "Farnsworth, Dave"
<DFarnsworth_at_Ashleyfurniture.com> wrote:
> I have to share this post I got on another list.
> Someone had asked a
> question about how Oracle locks work, here is the
> question.......
>
> Q: i'd like to understand the lock modes
> (share & exclusive)
> & how to make them on table in DML transaction & why
> locking is
> automatically use the lowest level of
> restrictiveness
> & how the read consistency occures
>
>
> Here is the response someone sent................
>
> An Oracle table is like a public restroom with an
> open door.
>
> When you go in to use the restroom, you shut the
> door as you
> enter, and you have placed the bathroom in shared
> lock mode.
> When another person want to use the restroom too,
> they can
> push open the door and enter. Both of you are now in
> the
> restroom and sharing it.
>
> However, if you go into the restroom, shut the door,
> and also
> lock it, then you have acquired the restroom in
> exclusive lock
> mode. Nobody else can come into the bathroom, even
> though there
> are multiple stalls in there: your exclusiveness
> prevents anybody
> else from going in there.
>
> In a third situation, you go into the restroom in
> shared mode,
> and then somebody else comes in after you, then it
> would be
> very presumptious of him to lock the door behind him
> because
> it just isn't done for someone to lock another
> stranger into
> the restroom; it would also make you very
> apprehensive to know
> that he's now locked you in there with him. So, if
> someone
> already is in the restroom and is sharing it, it
> prohibits
> someone else from coming in later and claiming
> exclusivity
> on it (at least not until the first person leaves.)
>
> So, when you acquire the restroom, you should use
> the lowest
> level of lockage, otherwise you're just being rude
> in not
> sharing use of the facilities, and you would
> probably cause
> a long queue of people outside the restroom causing
> contention
> problems waiting to gain access to the bathroom
> because it's
> been locked in exclusive mode.
>
> Now, suppose you set up web cams inside the restroom
> to
> take video images of the restroom and the stalls
> therein,
> and issue every one who enters virtual reality
> googles.
> The web cams guarantees users' privacy by use of
> read-
> consistency: the moment someone goes into a stall
> and closes
> the door, the web cam switches from live feed to
> replaying
> footage of an empty stall that was recorded from
> just prior
> to someone going into that stall. So, although there
> may be
> several people in the stall doing their business,
> your
> virtual reality googles always seem to show you
> clean, empty
> stalls. You pick an empty stall and try to enter it.
> If the
> stall is occupied, the stall door will be locked, so
> you
> can't enter it and do things to it, but through the
> magic
> of read-consistency, it looks as if it is unused; so
> like an
> obstinate idiot, you keep trying, and trying to open
> the door
> that won't open; at least not until the person in
> the stall
> comes out again, but you don't know that because
> your eyes
> tell you that the stall is free; you can see it, you
> just
> can't seem to be able to touch it. If the stall is
> truly
> unoccupied, you may enter and close the door behind
> you and
> now you have locked your stall record in exclusive
> mode
> (although the restroom as a whole can still be in
> shared
> mode; you just don't want anyone else with you in
> the stall
> itself.)
>
> After you do your business in the stall, and piss
> all over
> the toilet seat making a huge mess, you can either
> commit
> your work by just exiting the stall, exposing what
> you've
> done to the stall to all the other web cams now
> looking in
> on your messy, empty stall; or you can rollback your
> work
> by cleaning up the mess so that when you exit,
> nobody else
> is the wiser that you peed with the toilet seat
> down. The
> moment you commit or rollback by exiting the stall,
> your
> claim on the stall is released, and someone else may
> now
> acquire the stall.
>
> So, the lesson to be learnt here is: either learn to
> piss
> sitting down, or raise the seat when you pee.
> --
> Please see the official ORACLE-L FAQ:
> http://www.orafaq.com
> --
> Author: Farnsworth, Dave
> INET: DFarnsworth_at_Ashleyfurniture.com
>
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--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Deepak Thapliyal
INET: deepakthapliyal_at_yahoo.com
Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
San Diego, California -- Public Internet access / Mailing Lists
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Received on Tue Dec 11 2001 - 16:32:14 CST
