Both InnoDB and PostgreSQL - as well as many other databases - use a technique called multi-version concurrency control (MVCC) to provide transaction isolation: transactions should not see the work of other, uncommitted transactions. MVCC means that, when a row is updated, the database stores both the old and new versions of the row.


Showing posts with label system admin. Show all posts
Showing posts with label system admin. Show all posts

Thursday, January 3, 2013

Kernel Panic - Fallback to Old Kernel

Few days back, i was testing a kernel module, unfortunately it didn't work and instantly after reboot, kernel Panic occurs. Well i was clueless what goes wrong, but now i can not select the older kernel version to boot. But, there is a way out, if we choose these first before reboot (off course after installing new kernel), and this is inbuilt in GRUB. This mechanism is called Grub Fall-back. In this case you can set your older/tested kernel as the Fallback kernel in case new kernel panics. And here is how you do it:All you have to do is to open your /boot/grub/grub.conf and add a few lines in it like this

Saturday, August 18, 2012

Citrix XenServer – iSCSI LUN

Hi all, here is my new Mini-Howto for Citrix XenServer – Storage Repository Over Software iSCSI LUN

Topic contains:
How to Create NFS and iSCSI LUN on Linux (I will CentOS)
How to mount them on Citrix Xen Server using Command line and GUI (that includes Screen Shots)

Tuesday, March 13, 2012


We need password less ssh login, so here i have tried to make the keys centralized by storing them in LDAP

LDAP Server Setup

[root@ldap]#  yum install openldap{,-clients,-devel,} nss_ldap

make entry in /etc/hosts    directory.domain.com

Tuesday, March 15, 2011

Monitor PostgreSQL with Queries

(Not All written by me.... )Some time just monitoring a DB servers from monitoring tools is just not enough, in that case we need some tool that let us know, what is DB is holding, processing, parameters etc..

Monday, January 24, 2011

Purge Bin_Logs, Save Disk Space - Mysql

Purge Bin_Logs Save Disk Space

Oftenly i meet with a question in mysql that, "How can I remove old mysql-bin log file in log directory?"

So here is the way... sort, good and practically proved.

Thursday, October 14, 2010

Linux Commands - Not Usual

Linux Command Tips

Check Validity of a Certificate File (PEM File)

# openssl x509 -in Certificates.pem -inform PEM -text -noout -enddate


What is IaaS or Private Cloud ?

What is IaaS or Private Cloud? And why Enterprise should consider it?

The shortest definition could be. ‘Virtualization on top of an HPC’. Let’s define it like this. What do you think is the biggest limitation to virtualization?

Monitor File Activities - Using iWatch

Monitor File Activities - iWatch

We frequently meet situation, like some files or directories that supposed to secure are having some operations on it, like read, open, close, write etc...

And many times people would like to have a monitoring tool to monitor files activities.

Here’s a solution for this, I got a tool “iWatch”, written in Perl and can also work in Daemon mode.

This tool can be used as to monitor/detect unwanted manipulation on file system and report it to system admins.

RSYNC Server - A Remote File Transfer Protocol - Server Migration Tool


Remote file transfer protocol

Rsync is a linux in-built file transfer program that is similar to RCP or SCP. It includes the added feature of allowing just the differences between two sets of files on two machines to be transferred across the network.  

Rsync sends un-encrypted traffic over the network, but can this can also be tunneled through SSH.

The Rsync listens on port 873.

Create RAID on CentOS


First let's understand the term RAID
RAID basically stands for Redundant Array of Inexpensive Disk
RAID is used for Implementing Fastness in reading, writing, and Redundancy on DISks

RAID types:
1: Software RAID
2: Hardware RAID
3: Fake RAID

LDAP - Authentication server for SSH and SVN

LDAP as Auth server for Users  ---- With SSH and SVNThis HOW TO belongs to those, who have some funda about LDAP, SVN, Apache

Prepare LDAP Server:

yum install openldap{,-clients,-devel,} nss_ldap