Monitoring Load average

Load average represents the number of processes waiting in the OS scheduler queue. Unlike CPU, load average will increase when any resource is limited (e.g. CPU, network, disk, memory etc.). Please refer to the blog “Understanding Linux Load Average” for more details.
We can use the following load average values to decide whether a machine is loaded

• If load average < number of cores, then the machine is not loaded
• If load average == number of cores, then the machine is in full use
• If load average >= 4X number of cores, then the machine is highly loaded
• If load average >= around 40X number of cores, then the machine is unusable

One mistake often made is profiling the CPU without first determining whether it is truly a CPU bound use case. Although CPU utilization shown by top command is low, machine may be busy doing IO (e.g. reading disk, writing to network). Load average is a much better metric for determining whether the machine is loaded.

Generally three figures are seen in top or uptime command for load average, something like -
1.08, 0.8. 4.0. This means load average over 1,5 and 15 mins.

In top command, at the top-right hand corner you should see your load averages displayed as three numbers. These numbers are setup as follows:

Load Averages: 1.00 2.00 3.00
1.00 - 1 Minute average
2.00 - 5 Minute average
3.00 - 15 Minute average

In the example above, these load averages would indicate that 15 minutes ago the server was averaging a load of 3.00, while 5 minutes ago it was averaging a load of 2.00, and over the last minute it's been averaging a load of 1.00. This means that over the course of 15 minutes the server was doing a lot of work, 5 minutes ago it cut that workload in half, and then within the last minute it was cut in half again.

The Linux load average on a server is a rough estimate of the workload currently waiting to process.

Difference between Purge and Delete.

Purge - 
To systematically and permanently remove old and unneeded data. The term purge is stronger than delete. It is often possible to regain deleted objects by undeleting them, but purged objects are gone forever.

 

Why they say its difficult to manage software in case where database triggers are used

Came across a problem where an insert query was failing to write to a table with error - Duplicate primary key. Interesting part was that the table did not have a primay key. After spending some time it was noticed that there were two trigger configured for the table. One for insert and other for update. The insert trigger writes the same record in some other table which had the primary key constrain which was failing if the same insert query is executed twice.