Numbers to Remember

Question 1

The total number of seconds in a day?

Answer 1

1,00,000

Question 2

The average size of one image?

Answer 2

100 KB

Question 3

The specs (disk, RAM, cores, threads) for one commodity server?

Answer 3

4 TB / 128 GB / 12 CPU cores / 100 Threads
(8 threads per core)

Question 4

Frames per sec (FPS) in a video?

Answer 4

24

Question 5

The average video size per minute?
(24 fps, 100 KB frame)

Answer 5

100 MB / minute

Question 6

The number of days in 3 years?

Answer 6

1000

Question 7

Round Trip Time (RTT) from US West Coast to East Coast?

Answer 7

100 msec

Question 8

Round Trip Time (RTT) from US West Coast to Europe?

Answer 8

200 msec

Question 9

Round Trip Time (RTT) from US West Coast to India?

Answer 9

400 msec

Question 10

The max size of a long URL?

Answer 10

2048 bytes

Question 11

The length of the MD5 hash?

Answer 11

128 bits

Question 12

The length of the SHA1 hash?

Answer 12

160 bits

Question 13

The length of the CRC-8, CRC-16 & CRC-32 checksums?

Answer 13

8 bits, 16 bits, 32 bits

Question 14

The time it takes to compute the bcrypt hash and MD5 hash respectively?

Answer 14

300 msec, 300 nsec

Question 15

The read and write throughput of SSD?

Answer 15

1 GB / sec: Read
100 MB / sec: Write

Question 16

To achieve a 90% cache hit rate what percentage of entries do we need to cache?

Answer 16

10%

Question 17

To achieve a 99% cache hit rate what percentage of entries do we need to cache?

Answer 17

30%

Question 18

What will be the cache hit rate if 10% of entries are kept in the cache?

Answer 18

90%

Question 19

What will be the cache hit rate if 30% of entries are kept in the cache?

Answer 19

99%

Question 20

The number of Gmail users?

Answer 20

2 Billion

Question 21

The number of Facebook users?

Answer 21

3 Billion

Question 22

The number of Instagram users?

Answer 22

1 Billion

Question 23

The number of Twitter users?

Answer 23

300 Million

Question 24

The number of Whatsapp users?

Answer 24

3 Billion

Question 25

The number of Linkedin users?

Answer 25

1 Billion

Question 26

The number of Uber users?

Answer 26

100 Million

Question 27

The number of Dropbox users?

Answer 27

700 Million

Question 28

How much CPU load shall be considered while provisioning?
Why?

Answer 28

40%.
It can handle 2x load beyond which autoscaling is required which typically takes some time to come up.

Question 29

What length of Geohash is required to scan a circle of 5 KMs (assuming base 32 Geohash)?

Answer 29

5 characters

Question 30

What is the Query per sec (QPS) limit on a commodity server?

Answer 30

40,000 / t (in msec)

Question 31

The length of the MurMur3 hash (Cassandra)?

Answer 31

64 bit
-2^63 to 2^63+1

Question 32

What is the total number of Amazon India (eCommerce) users and listed products?

Answer 32

100M users and 100M products.
100 orders/sec

Question 33

What is the Sequential Read/Write capacity of HDD drives (7200 RPM)?

Answer 33

100 MB/sec

Question 34

What is the Sequential Read/Write capacity of SSD drives (SATA 3.0)?

Answer 34

500 MB/sec

Question 35

The time it take to read/write from memory?

Answer 35

100 nsec

Question 36

Network RTT between two machines (intra-zone)

Answer 36

50 usec

Question 37

Size of log for logging one web request

Answer 37

1 K

Question 38

Max Round trips b/w two machines (intra-zone)?

Answer 38

20K (based on 50 usec latency)

Question 39

Throughput and latency comparison of Kafka and RabbitMQ?

Answer 39

Kafka: 200K msgs/sec, 20 msec
RabbitMQ: 25K msgs/sec, 2 msec

Question 40

Unique ID generation: How many bits for timestamp to store 34 years worth of Msec?

Answer 40

40 bits