IDS Forum

Re: Symlinks and informix...

Posted By: Art Kagel
Date: Tuesday, 27 January 2009, at 9:17 a.m.

In Response To: RE: Symlinks and informix... (Jarrod Teale)

OK, the RPM install should NOT be removing the existing software whether the
engine is online or not!

You should ALWAYS have two, and sometimes three, versions of the IDS
software on disk at all times:

1. The currently running version

2. The previous version in case you have to revert due to problems with

the newer software

3. Sometimes, between installation and starting the new version you'll

also have the next version on disk.

So, how to fix this. The RPM should not be removing /usr/informix or the
previous installed version. It should be trying to remove any previously
installed copy of the same new version. In this case it should be removing
any existing copy of 11.10.UC3 not 11.10.UC2. That solves your device
problems and the install script can copy the device links to the new install
directory post-install at the same time that it copies the sqlhosts and
ONCONFIG files. Then there's no conflict and no need to remove the existing
chunk links.

Art

On Mon, Jan 26, 2009 at 8:59 PM, Jarrod Teale <Jarrod.Teale@fonterra.com>wrote:

> Okay - so the reason.
>
> We deploy everything using the RedHat RPM system - including the base
> setup of the informix engine.
> When the package for 11.10.UC2W2 was built, the author added the
> /usr/informix/DBSPACES directory to the package - making it owned by it.
> If you then build a package to deploy 11.50.UC3 binaries and perform a
> silent install into a different informix directory then you have the new
> version of the engine installed and ready to pick up when the
> INFORMIXDIR is changed and the instance cycled.
> This is great - except that the upgrade to 11.50.UC3 removes the package
> for 11.10.UC2W2 - along with all files it owns. 99% of these are just
> the install media and scripts so harmless. But the DBSPACES directory is
> really important as the engine is still running at the time.
>
> The workaround we came up with was to push out a package that removed
> ownership of the files from the RPM system - but to do that we have to
> allow the RPM system to rip out the symlinks and then create them using
> a post script so they are there, but not owned.
>
> In brief:
> 11.10.UC2W2 is installed into /usr/informix11UC2W2
> 11.50.UC3 is being installed into /usr/informix115UC3
> 10.0.UC6 is also installed in /usr/informix10
> The running engine has INFORMIXDIR set to /usr/informix
> /usr/informix is a symlink to the installed set of binaries that we have
> the engine running on.
> Upgrade is to install the new version at the DBA's convienence then when
> an outage can be achieved (may be months later) swap the /usr/informix
> symlink to the new binary directory and let it migrate (testing all
> completed ahead of time - there are 25ish of these identical systems).
>
> Stupidly the directory with the chunks from the engines point of view is
> in /usr/informix/DBSPACES - which is in the underlying binary directory
> which is where the problem begins.
> We all know that changing this now (moving the chunks) is not easy
> (though not impossible).
>
> The problem arises when the 11.50.UC3 package hits the server and
> removes the content from the 11.10.UC2W2 directory (and the engine is
> running).
>
> Jarrod
> -----Original Message-----
> From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of
> Art Kagel
> Sent: Tuesday, 27 January 2009 1:43 p.m.
> To: ids@iiug.org
> Subject: Re: Symlinks and informix... [14637]
>
> Jarrod,
>
> IDS opens and closes the chunks periodically. If you run fuser against
> the chunks you will often note that they are not all opened by all of
> the CPU VPs. If a VP hasn't needed to perform IO against a chunk it will
> not have th chunk open. Existing open files in the engine will not be
> affected if you remove the links, and once the links have been
> reestablished to the existing chunks (I assume you aren't going to link
> them elsewhere while the engine is running) the engine should not notice
> that they were gone for a bit, but if the engine tries to open the
> chunks while the links are down all hell will break loose.
>
> I agree with others. Why do this at all?
>
> Art
>
> On Mon, Jan 26, 2009 at 5:42 PM, Jarrod Teale
> <Jarrod.Teale@fonterra.com>wrote:
>
> > Hey all.
> > Now I know that creating symlinks for access to chunks is a really
> > really good idea and is a practice that we follow religiously.
> > I have a question though - when does the database engine make use of
> > them? Is it just at startup when the chunks are going through sanity
> > checking?
> > Obviously I'm not counting any interaction with onspaces or admin/task
>
> > operation that add/remove/manipulate allocated disk - required then.
> >
> > The reason I ask is that we are looking at building a script that
> > destroys and then recreates them while the engine is running.
> > My assumption is that the engine creates the file handles it requires
> > to the chunks on startup and then doesn't need them again - so
> > destroying and recreating them won't cause a problem.
> >
> > It would be better to do while the engine is off-line, but in this
> > case we are hoping to avoid the downtime.
> >
> > We are on RedHat EL4 x86 (11.10.UC2W2 and 11.50.UC3).
> >
> > Thanks
> >
> > Jarrod Teale
> >
> > Team Lead - Manufacturing Execution Systems
> >
> > Automation & Process Control Group
> >
> > NZ Technical
> >
> > Fonterra
> >
> > Fonterra Extn: 77525
> >
> > DDI: +64 7 850 7525
> >
> > Mobile: +64 21 968 364
> > fax: +64 7 849 7855
> > email: jarrod.teale@fonterra.com
> > <mailto:jarrod.teale@fonterra.com>
> >
> >
> >
> >
> ************************************************************************
> *******
> > Forum Note: Use "Reply" to post a response in the discussion forum.
> >
> >
>
> --
> Art S. Kagel
> Oninit (www.oninit.com)
> IIUG Board of Directors (art@iiug.org)
>
> Disclaimer: Please keep in mind that my own opinions are my own opinions
> and do not reflect on my employer, Oninit, the IIUG, nor any other
> organization with which I am associated either explicitly or implicitly.
> Neither do those opinions reflect those of other individuals affiliated
> with any entity with which I am affiliated nor those of the entities
> themselves.
>
> --001636c5a1fb19ed9904616c2253
>
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--
Art S. Kagel
Oninit (www.oninit.com)
IIUG Board of Directors (art@iiug.org)

Disclaimer: Please keep in mind that my own opinions are my own opinions and
do not reflect on my employer, Oninit, the IIUG, nor any other organization
with which I am associated either explicitly or implicitly. Neither do
those opinions reflect those of other individuals affiliated with any entity
with which I am affiliated nor those of the entities themselves.

--001636c5bf725a186e046177850c

Messages In This Thread

• Symlinks and informix...
  Jarrod Teale -- Monday, 26 January 2009, at 5:42 p.m.
  • Re: Symlinks and informix...
    Keith Simmons -- Monday, 26 January 2009, at 7:19 p.m.
  • Re: Symlinks and informix...
    Art Kagel -- Monday, 26 January 2009, at 7:42 p.m.
    • RE: Symlinks and informix...
      Jarrod Teale -- Monday, 26 January 2009, at 8:59 p.m.
      • Re: Symlinks and informix...
        Obnoxio The Clown -- Tuesday, 27 January 2009, at 2:38 a.m.
      • Re: Symlinks and informix...
        Art Kagel -- Tuesday, 27 January 2009, at 9:17 a.m.

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