WHAT IS A VARIABLE?

VARIABLE: 

A variable is a letter or a symbol which represents some quantity (like numbers etc.).

Example: 55-y = 23 (Here ‘y’ is a variable)

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Difference between Equation and Expression in Mathematics

EXPRESSION: 

Examples: 5x-2y,  Ax+By (A,B are constants and x, y are variables) etc., 

EQUATION: 

An expression which equates to some other quantity.

Examples: 5x-2y=3, Ax+Cy=0 (A, B are constants and x, y are variables) etc.

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Difference between straight through, crossover and rollover cables.

Straight through:

Straight through cables, the wires connect to the same pins on either side of the cable. These cables are primarily used for connecting unlike devices like router to switch, computer to switch, hub to switch etc.

Cross over:

Cross over cables are similar to straight through cables, except that they have pairs of wires that crisscross. This allows for two devices to communicate at same time. The cables are primarily used for connecting like devices.

Roll over cables:

Roll over cables essentially have one end of the cable wired exactly opposite from the other. This usually connect a device to a router or switch’s console port.

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Some error interpretation from Cassandra system.log file

1) grep MutationStage system.log

First value is num active, second is number pending

2) grep DroppedMessagesLogger system.log

3) grep large system.log

Preliminary verification on Cassandra failures

1) for i in dc1 dc2; do for j in cass solr; do for k in 1 2 3 4; do l=pramod$j-$i-a${k}s; printf "%-20s " $l; nodetool -h $l -u cassandra -pw CassandraJMXPass  status | wc -l; done; done; done

2) nmap -P0 -p 7199 127.0.0.1

3) netstat -an|grep -i listen

4) ps -p PID -o etime

5) echo $(($(date +%s%N)/1000000))