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Oracle 11.2 and the direct path read event

In my previous post I touched the topic of a “new” codepath (codepath means “way of utilising the operating system”) for of full segment scans. Full segment scan means scanning a segment (I use “segment” because it could be a partition of a table or index) which is visible commonly visible in an explain plan (but not restricted to) as the rowsources “TABLE ACCESS FULL”, “FAST FULL INDEX SCAN” and “BITMAP FULL SCAN”.

Look at my presentation About multiblock reads to see how and when direct path reads kick in, and what the difference between the two is. Most notably, Oracle has released very little information about asynchronous direct path reads.

Oracle Linux support in ESXi

For quite some time now I am using ESXi 5 update 1 for my lab server and I’m very happy with it. In my lab environment I am not too picky what to run and do not worry about support too much. It’s not production!

One area of concern has been the support for Oracle’s own kernel: UEK or Unbreakable Enterprise Kernel. UEK comes in two editions, one based on 2.6.32, just like Red Hat’s kernel for Red Hat 6. The difference is that you can get UEK/1 (2.6.32.xxx) for Oracle Linux 5.x as well instead of 2.6.18xxx which is otherwise the default.

Oracle’s second iteration of kernel UEK is unsurprisingly named UEK2 and it’s initially based on 3.x but keeps the name to 2.6.39.x for compatibility reasons. UEK2 has some really nice features taken from the Upstream kernel and it is also supported for the Oracle database.

Oracle 11.2.0.1 and the ‘kfk: async disk IO’ wait event

Recently I was discussing some IO related waits with some friends. The wait I was discussing was ‘kfk: async disk IO’. This wait was always visible in Oracle version 11.2.0.1 and seems to be gone in version 11.2.0.2 and above. Here is the result of some investigation into that.

First: the wait is not gone with version 11.2.0.2 and above, which is very simple to prove (this is a database version 11.2.0.3):

Who Stole gettimeofday() System Calls From Oracle strace() sessions?

I've been meaning to write this blog post for a while now but never seemed to find the time. Hopefully this posting will be useful information for anyone that spends a lot of time tracing processes in Oracle from the Linux Operating System. I'm one of those people, so it was good to get to […]

Who Stole gettimeofday() System Calls From Oracle strace() sessions?

I've been meaning to write this blog post for a while now but never seemed to find the time. Hopefully this posting will be useful information for anyone that spends a lot of time tracing processes in Oracle from the Linux Operating System. I'm one of those people, so it was good to get to […]

Throttling IO with Linux

Why?

I guess the first question which comes to mind when reading this title is ‘Why’? For a database, but I guess for any IO depended application, we want IO’s to be faster, not throttle them, alias make them slower. Well, the ‘why’ is: if you want to investigate IO’s, you sometimes want them to slow down, so it’s easier to see them. Also, (not so) recent improvements in the Oracle database made great progress in being able to use the available bandwidth by doing IO in parallel, which could strip away much of the ability to see them in Oracle’s popular SQL trace.

Adding disks to VMware Workstation 8 on the fly on RHEL 6

Although this post is primarily written for users of VMware Workstation 8 it is applicable for any RedHat 6 clone and adding disks with single path on the fly. Multipathing requires additional setup in dm-multipath or the vendor multipathing software which I won’t cover here. A quick hint though: you need to set disk.EnableUUID = “TRUE” in your VM’s config file for scsi_id to return a value.

The situation is common: you created a virtual machine and need more storage. Hopefully you created it using LVM which would allow you to add the new disk to an existing volume group followed by a resize operation of the logical volume which is short on space. But before you can do this you have to add a new LUN to your setup-here is how you can do this without rebooting the VM.

First I recommend you install lsscsi (for convenience, not really necessary) and the sg3_utils:

UltraEdit 3.3 for Mac/Linux…

I’m now rockin’ UltraEdit 3.3 on my MacBook Pro and Linux boxes at home. A previous announcement suggested by this version the Mac and Linux versions would have caught up with the Windows version from a functionality perspective. I’m not sure if that’s true, but they are close enough for me.

The latest Windows versions is 18.20, which I use at work, but home is where the real magic happens. :)

Cheers

Tim…

 

How to rename NIC in OEL 6.X

This is a quick note about host cloning and network interface (ethX) renaming.
As I wrote in my last post I have ESX lab now and I create a template of OEL 6.3 with all my settings and I would like use it for adding new VM (including RAC nodes). It is easy but there is one small issue – every time you clone VM network devices are renamed. Well MAC address is unique so it doesn’t surprise me but I would like to keep interface names like eth0, eth1 and eth2 and I got eth0, eth3, eth4 instead. Since OEL 5 (Redhat 5) all device name are generated by udev mechanism so I start my research there.
Well it was easier than I thought – there is a file in "/udev/rules.d" directory called "70-persistent-net.rules".

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