Section 3.3. PI Server Data
Flow. What we are talking about in this section is
we are just going to kind of round out some of the
things from this illustration we have seen before. We will talk about the Event Queue
and the Archive and some of the other structures
that you will see on its way to, on, on --
as the data moves towards the actual on-line archives.
And, by the way, do not let the word archive
confuse you. The archives are on line --
the data that we keep on line. They are not stored off
somewhere, although, obviously, backups of them can be.
So let's take a look at this Event Queue File. Let's discuss it briefly.
The Event Queue File is, it is a,
a physical file that buffers the,
the process data as it's on its way
to the archive. So, let's go revisit this illustration again.
We are talking about this file right here, this Event
Queue file. It is,
it is, as I said, a kind of a wave point
on, on the journey to the archive.
And, normally we
simply take the data out of that Event Queue
and send it over to the PI Archive
Subsystem which subsequently puts it into the
cache and then the archive. But, occasionally, you will find,
well, that there are certain things that can happen that will interrupt this.
Let me just kind of list some of those things that can happen. For
example, if the offline -- or if the archive
process itself, for whatever reason, if this process fails,
that process fails, then we are going to have some problems
storing data, so we want to queue it somewhere. Also,
if you have some huge surge in the amount of
process data. Let's say you are just being overwhelmed with a tremendous
amount of data coming in this direction,
then the Event Queue can kick in to handle that overload.
And also, if it's just the
CPU that's overloading. If you have a lot of activity on
the server then the Event Queue can handle.
Since this is RAM Resident, this
is something it can handle much faster than the
physical writing to disk that happens with the archive
cache writing to the archive.
Now,
there are certain things about this file as it behaves
you should know about. First of all, once that file's
full in memory, we are going to go ahead and rename that file
and then create a new one. Now the default
location of this is here,
pimapevq.dat. I stated that
incorrectly a little earlier in the course. I think I called it
pieventqueue.dot. That's actually the old name for it, but it's now
currently called pimapevq.dat.
And, if you recall, during the installation we got to choose
what the size of it was. And so we chose the default which was
64 MB. The recommendation is to make this half the
size of an archive, and, and since there
really -- the only limitation to its utility is
the amount of free space on that disk drive, then we do
suggest you keep adequate free space to,
well, to handle, for example, a,
an archive process that stops on a Friday afternoon
when everybody's gone home and, and does not get
tended to until maybe Tuesday after a 3-day weekend.
You know, you want to make sure you have got enough free disk space to account for
some kind of a worse case scenario like that.
Now, there are some parameters that can be changed
using the tuning parameters. So, let me switch over,
show you again where this is.
If you go into the Operations Section,
under Tuning Parameters,
this is where you would see, or this
is where we can go in and makes changes to things like
the size of this online archive --
or I am sorry, the online, this online
queue. So, if you go into the Snapshot Section,
you will see here's the Event Queue size and Event
Queue path, etc.
And as I mentioned before, you would find this Event Queue in the
pi-dat directory. It's called
pimapevq.dat.
I missed it. There we go.
Pimapevq.dat. And the reason we are discussing this is
because as a, as a system manager, sometimes
you are going to witness this kind of an Event Queue grow
and, of course, we would, at that point, suggest you
give us a call in tech support. On tech support we would
very likely step you through the process
of troubleshooting -- you know, where is the problem? Is the problem
with some kind of a disconnect?
With these processes here, if the process
of the archive subsystem is no longer running properly,
or if maybe it's been stalled during a backup,
we will try to get that resolved. And then, once that's
been resolved, we will suggest that you watch to see
if those Event Queue files are being recovered properly.
So the reason we discuss this is because there are occasionally
times when you are going to look at the activity of that Event Queue,
and be talking to tech support on,
on recovering that data once it's been queued up.
Now, sometimes, if
you do have some kind of an Event Queue File or series of
files that grows, and you have, you have just recovered
the process so that the archive process is back on line,
and we are starting to recover that Event Queue File, you may
find a situation in which the ability for the
archive process to recover that queue just is not
going to keep up with the amount of new data you are getting. So actually,
you will find that the queue is growing and growing from the end
as we are, as we are trying to recover
from the beginning of that queue. You can get into a situation
where basically the system will never ever catch up.
Well, there's things that we can suggest you do if that happens.
On tech support they will, they will go through the process of,
you know, showing you how to increase the priority of the process, for example.
But, sometimes it, it just ends up
that the best way to do this is to reprocess it later on.
So, sometimes you will find that what we will suggest you do
is just stop the processes, rename the Event
Queue, and then reprocess that later on,
either later when the system's not as busy, or even using
what we call our offline Archive Subsystem to
reprocess this into a, a clone of your system to
kind of reprocess this into archives offline
and then put those archives back online on your production
system. Now, again, we would not recommend any of that
without having somebody from tech support
on the phone, or a tech support
document, one of our tech,
tech notes, that describes how to go though that. So,
if you are in a situation like that, of course,
give us a call in tech support and we will step you through the process.