Critical uptime question (Was "Looking for some upgrade advice")

[John Esak]

  -----Original Message-----
  From: Boaz Bezborodko [mailto:boaz at mirrotek.com]
  Sent: Sunday, May 21, 2006 10:17 PM
  To: filepro-list at lists.celestial.com; John Esak
  Subject: Critical uptime question (Was "Looking for some upgrade advice")




  John Esak wrote:
Date: Fri, 19 May 2006 07:37:16 -0400
From: "John Esak" <john at valar.com>
Subject: OT: RE: Looking for some upgrade advice
To: "Fplist (E-mail)" <filepro-list at seaslug.org>
Cc: Rick Walsh <rick at nexusplastics.com>
Message-ID: <JIECJPPMJGMIINMGGNGAAEHJPBAA.john at valar.com>
Content-Type: text/plain;	charset="us-ascii"

  I suspect the only reason I haven't seen comparable uptimes on my linux
systems is because the kernel updates require a reboot.  I talked directly
to the 2nd in charge of the kernel, as well as some of the other kernel
devs, and the consensus was that if I wanted a hot-swappable kernel, I
could go and write the hot-swap code myself.  They didn't consider it a
priority, or even desirable.

As you know, the *last* thing in the world I want to do is start a Linux
thread here. :-)

BUT... this is something I hadn't considered in our upcoming major move to
SuSe Linux. We have a situation where the main *nix server (currently SCO
OpenServer 5.6) can NOT go down at all. Literally, it is used to produce
various things, mostly bar code lables 365/24/7... with absolutely NO down
time at all except for two week long vacations during the year and some
other extremely special circumstances... hardly would I called these
"planned maintenance"... mor like get in whatever we can because the system
went down for some unforeseen reason! :-)  Very occasionally, and I mean
very occasionally, we can stop the constant transactional postings (and
label printing) for a few minutes... rally, just a few. Otherwise, it
becomes much like the "I Love Lucy" chocolate factory conveyor belt scene.

What, seriously, are we going to do in this situation. I was kin of hoping
we could find a *stable* Linux... meaning a kernel that does not need that
much or *any* patching. Are you talking about real security problems, or
feature upgrades? We simply can not bring the mahcine down for either
reason... at least not on *any* kind of ongoing basis.... how in the world
does *anyone* cope with such a situation.

Yes, yes, I'm constantly considering and devising possible methods to
de-reference our main databases and CPU's from this immediate hardware
interface... but to date, I have not come up with anything that would work
well enough to meet the need. Our systems are currently up-to-the-minute and
pretty much *have* to stay that way.

Suggestions?

John Esak

  John,

  I was thinking about this over the weekend.  It seems to me that you could
give yourself a whole lot of flexibility if you could somehow duplicate the
database you're working with.  I think that I could do this if the database
was not stored on the same machine as that which is executing the filePro
code.

  Here is how I see it working:
  Run two different servers each with its own copy of the database files.
One is the one that is directly accessed by the users while the other gets
updated with all of its transactions.  Whenever it gets a transaction it
generates a record of the transaction as a separate file for the second
database to read.  The second database would have a process that will look
for these transactions and update the files on its database.

  You could set up a controlled switch from the server running the first
database to the one running the second database.  At the end of each
transaction executed on the data of the primary database you can have code
that will check some status flag as to the condition of the server of that
database.  You can program the process to force the user to exit out of the
application if it sees a flag that tells it to switch to the secondary
database files.  Once it exits you change the clients' configuration to work
from the secondary database upon re-execution.  All transactions will
eventually move on to the second database server until all processes have
transfered leaving the first free for any changes or updates.  In the
meantime that secondary database has now started acting as the primary
database and is building up a list of transactions that the original
database will have to update to bring it to the same condition as the first
once it is started up again.  (Or you might be able to just copy files.)

  I don't know much about Linux, but I could see how an application working
on the same computer as the data would have a much harder time detecting and
adjusting for a switch to run off a different server.  But if all you're
doing is going to a virtual drive similar to how I do it now--by running the
processes on separate windows machines while they look to mapped network
drives for the data--it is a much easier process to have a script that will
exit out of the process, change the mapped network drive to point to the new
server, and then re execute.

  It seems like this will work well enough, but not knowing the actual
application I don't know if this is a good solution for you.

  Boaz


  I certainly appreciate the suggestion. however....  Well, I don't exactly
know how to state the however's... except that unfortunately, I think you
have minimized the do-ability of the procedures you are suggesting.  if
filePro were a true RDBMS system with all that this entails  (a la
Codd/Date) then yes, this would be possible.  With filePro being what it
is... a flat file system using code written in this case by me or Rick to
make it function... there is I'm afraid to say, no viable way to emulate the
massive and deeply entwined   transactional nature of such databases.

  I don't mean to belittle the programming genius of either myself or my
colleague, Rick.  :-)  At least 200 people on this list will certify that I
feel I am the best filePro programmer in the world... :-)  and have stated
so many times.  :-)  Is that enough smiley's to let everyone know that I am
fully aware that once you reach a certain level of ability, the most you can
be is occasionally first among equals... and there are a hell of a lot of
"equal" filePro programmers out there to me... possibly even yourself... but
of course I don't know you or your prowess so I'll just give you the benefit
of the doubt and guess that you are thoroughly capable of writing whatever
you want in filePro as the rest of us.  HOWEVER, and finally it comes...
there is simply no way and no one I know, including even Ken (either Brody
or White) who could possibly do what you suggest.  The reasons are many, but
mostly they lay in the misnomer of filePro itself and sometimes just
datasets themselves and Oracle all being called a "database".  Truly, if I
could cull out the particular "database" as you are referring to it and
manipulate a transaction log and transaction data file in the right ways, I
could move between two application servers... maybe, possibly.... perhaps...
The reality, however, (there's that word again) is that I have more than 700
active data files, thousands of processing procedures, and hundreds of
system/shell scripts to do the work in any particular sub-application of
what goes on at Nexus. If the module at hand interfaces with our gut-level
accounting system (also completely filePro based), then many dozens of any
of these several hundreds/thousands of items may have to interact... and in
a very tightly knit way.  The task of building in (from within filePro
itself) some registering, transactional  process is not only daunting, but,
I think, impossible. I am certain, after many years of contemplating such
things... and even implementing many smaller subsets of this idea for myself
and others... that on a large full-scale basis, the only way to do it with
full fail-safe operation is to have the process and control already built-in
to the RDBMS itself... as it, of course, is in those systems. In other
words, I wouldn't ever try "duplicating" this with filePro. I am one of the
longest-standing, loudest proponents of filePro and all that it can do,
which is nothing short of staggering... but I am also a realist and know it
is not internally capable of working in this way.

  The most I can hope for  is a methodology wherein all of our machinery
that is "tied" to filePro can be simultaneously paused for a specified
length of time during which a controlled transfer to a duplicate system can
be managed.  Along with this nearly impossible task, a controlled transfer
of all user processes to the duplicate system must also be attained... and
this is even harder to conceive.  It can be planned and done (mostly in a
manual way) making sure IP's and all related matters are dealt with
properly... but it has never been something I am capable of handling
"automatically".


  Short of absolutely pausing "production" for some length of time, there is
no cut-over or fail-over procedure which can be accomplished as our system
now sits.  We can immediately fail-over from communications lines failures
like T1's going down between plants... but if the "main" server itself
fails, we always have a 15 minute to 30 minute period of real havoc and
repair that has to go on before things are back to normal on either "main"
or  "duplicate" server.  I hate the situation, but as I said, haven't been
able to come up with a solution yet.

  We have looked into some of the older "mirroring server" software
solutions, but they are extremely expensive and never seem to guarantee that
what we are  looking for ... is what they provide.  If you, or anyone, know
such a system, speak up.  The old days of 1776 and others like that are
gone.  At least, our searches for such a solution do not ever include SCO
Open Server.  Perhaps, we will have more luck with Linux.  (Although, I
don't have high hopes for an affordable solution.

  In the very first place, no one has considered the "licensing" for a
completely hot-swappable server?  In terms of filePro, I think it was
brought up during the beta testing for 5.6, but I don't remember if there
was a precise plan regarding this.  Imagine that I did have a pair of
mirrored servers, would I need to get a license for both  machines?  I
wouldn't think so, but it is part of the whole cost thing to some degree.

  Sorry to be so wordy in all this... and yes, I would be thoroughly happy
if someone were to say, why haven't you checked out "thus-and-such" it does
exactly what you need... but I don't think it is going to happen.

  And to get back to your suggestion for just one second... I probably could
have stated all this in the few words....  "Good idea, but it is just too
hard for me to conceive of doing from within filePro."  :-)  I've been
waiting for a large download to finish... and had some time on my hands...
:-)


  John


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