Thursday Jan 23, 2014

Orale Learning Library(OBE) updates via RSS

Oracle By Examples, short videos, tutorials...
A lot of materials from many product lines are put in one place.
(Not all, unfortunately..)

Oracle Learning Library (OLL)

Most Popular in Last Month

  • Using Database Change Notification With ODP.NET and Oracle Database 11g Hits: 17,399

And here's RSS XML.

Oracle Learning Library: Recent Activity

Oracle Learning Library: Recent Activity

Description: Oracle Learning Library RSS Feed
What's New in Webcenter 11.1.1.8 (Recorded Webcast) 

Released On: 01/21/2014 An overview of

This RSS does one smart thing. It alternate its contents every 10x{n} minutes even when
nothing changes in the repository. For example, "Released On: 01/16/2014" changes to
"Released On: Jueves, 16 Enero, 2014" which is apparently Spanish!

The RSS reader I use is rss2email and it's easily fooled by this and show all entries as new multiple times.
I'm not sure if my RSS reader is too old or RSS XML is wrong.
If you think the latter is the case, please let me know. I'll try to contact the administrator.

Friday Jan 17, 2014

Inject filesystem I/O latency. Oracle Linux 5 and 6

I needed file I/O to take longer time for test purpose.
I needed latency on all files in a directory including newly created files.
I thought one of FUSE filesystem can be used here.

Filesystem in Userspace - Wikipedia, the free encyclopedia

Filesystem in Userspace (FUSE) is an operating system mechanism for Unix-like computer operating systems that lets non-privileged users create their own file systems without editing kernel code.

In my env, FUSE was already installed to use DBFS.

Using DBFS

dbfs_client host must have the FUSE Linux package

I haven't configured DBFS and I thought one of filesystem that stores data over the network
can become slow if I can simulate slow network.

So I tried SSHFS.
I could install "fuse-sshfs" rpm package both on Oracle Linux 5&6 via 'yum' command.
This package is on 'epel' channel. For OL6, I think there is 'rpm' just to set up this channel.
I don't remember where I found.
For OL5, I couldn't find the rpm so I googled and copy&pasted from this page.

The point of no return » Adding EPEL repository on CentOS

epel.repo file into /etc/yum.repos.d

Below is the test result.
As you can see, File I/O is now 100 times slower.
But since there could be other operations which uses loopback network, I think I will keep searching for a
safer way.

$ su -c "sshfs -o allow_other root@localhost:/root/sshfs_dir /mnt/tmp"
Password:
$ ping -c 1 localhost
PING localhost.localdomain (127.0.0.1) 56(84) bytes of data.
64 bytes from localhost.localdomain (127.0.0.1): icmp_seq=1 ttl=64 time=0.013 ms
$ time dd if=/dev/zero of=/mnt/tmp/128blocks.f bs=8192 count=128
128+0 records in
128+0 records out
1048576 bytes (1.0 MB) copied, 0.0590345 seconds, 17.8 MB/s

real    0m0.181s
user    0m0.000s
sys     0m0.003s
$ su - -c "tc qdisc add dev lo root netem delay 500ms"
Password:
$ ping -c 1 localhost
PING localhost.localdomain (127.0.0.1) 56(84) bytes of data.
64 bytes from localhost.localdomain (127.0.0.1): icmp_seq=1 ttl=64 time=1000 ms
$ time dd if=/dev/zero of=/mnt/tmp/128blocks.f bs=8192 count=128
128+0 records in
128+0 records out
1048576 bytes (1.0 MB) copied, 13.0411 seconds, 80.4 kB/s

real    0m19.084s
user    0m0.000s
sys     0m0.003s
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The views expressed on this blog are my own and do not necessarily reflect the views of Oracle.

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