Wednesday, April 27, 2011

Manual archiving of redo logs gone with 9i – or is it not?

Originally published on Dbvisit blog at http://blog.dbvisit.com/manual-archiving-of-redo-logs-gone-with-9i-or-is-it-not/.

If you memory dates back to the pre-10g times, you will maybe recall the steps to enable archivelog mode on the database at that time. Perhaps the greatest catch was that the online logs did not get archived automatically by default – you had to do it manually.

Or, let Oracle come to rescue, and let the ARCH process(es) do it for you by starting them with log_archive_start = true (or even dynamically with alter system archive log start/stop). You could even start ARCH in noarchivelog mode, so they did completely nothing, just writing error messages to alert.log.

One of the new features of 10g was getting rid of all of this – ARCH starting is governed solely by (no)archivelog mode and the DBA does not need to fiddle with anything else to get it right. Great applause, many thanks, scene over.

Well, all above is just a short transcript of my memory of those great times, and I lived with it happily and well till this week.

As it turns out, the story with 10g is not so straightforward – although it is true that if you just set no/archivelog mode that ARCH works as expected, the manual way of archiving was in fact not removed. But the way to enable it new:

To enable manual archiving mode, use alter database archivelog manual. The rest is the same as with 9i – use alter system archive log commands.

One consequence of this change – the log_mode in v$database can be archivelog, noarchivelog (as in 9i and before) or manual (from 10g on). This also means that if you want to detect whether a database runs in archivelog mode, you have to check for manual log_mode as well.

Sunday, April 24, 2011

Installing RAC on Oracle VM

Originally published on Dbvisit blog at http://blog.dbvisit.com/installing-rac-on-oracle-vm/.

One of the nice features of Oracle VM (and perhaps the most compelling one when you are evaluating different virtualization products for testing and development) is the comprehensive list of prepackaged templates available at Oracle e-delivery.

The list is not complete and probably cannot ever be, as Oracle is expanding it’s product offerings very fast. Of the missing basic configurations, there is for example no Oracle Database on Solaris template (although plain Solaris is available).

However, let’s look at the RAC templates. The list is comprehensive and you can choose between 11.1 and 11.2 on Oracle Enterprise Linux, both 32- and 64-bit.

The first-time setup is quite easy and easy if you follow supplied pdf documentation. The usual setup is 2-node RAC, but you can semi-manually add further nodes as well.

Still, there is a catch: the pdf declares that one of the prerequisities is to have two physical network cards. Strange, isn’t it? After all, a RAC node needs just one network card for the outside world, the second one connects just to the other nodes and should be virtual only, right? Well, not according to the docs. You have to set the second network interface of the RAC node to use xenbr1 (second network bridge) to connect to other nodes, but this bridge is simply not present in Oracle VM if you have just one physical network interface.

If you ignore the requirement and go on with the VM creation, you will face problems very soon: after you specify primary/secondary node (the first question after startup), the nodes don’t see each other. Or, they see each other, but after that, connectivity tests fail on eth1. (This differs on your choice of template used.)

The solution is in fact simple: if RACs need a separate xenbr1 bridge interface, just give it to them:

  • create the bridge: brctl addbr xenbr1
  • bring the bridge up: ifconfig xenbr1 up
And then, according to the docs, set the VIF1 interfaces to use xenbr1. If you do it by trial and error as I did, you may up end with VM assigning the VIFs incorrectly to the bridges (both to the same one, etc.). In that case edit vm.cfg for you virtual machine (in /OVS/running_pool/) and check that VIF0 is really set to xenbr0 and VIF1 to xenbr1. But if you first setup the xenbr1 and after that start creating your RAC, you should be fine.

As usual, to make the configuration permanent, you must make sure it persists reboots. Just adding the two aforementioned commands to /etc/rc.local should do the trick.