Measuring Efficiency

When describing the efficiency of a system, we look at a few different properties.

Latency

Latency describes the time it takes for a machine to perform a certain operation. Every method of retrieving information has different time costs. A general rule of thumb:

• Reading 1MB from RAM - 0.25ms
• Reading 1MB from SSD - 1ms
• Transfer 1MB over network - 10ms
• Reading 1MB from HDD - 20ms
• Intercontinental round-trip - 150ms

Throughput

While latency measures the time operations take, throughput describes the number of operations that can be processed in a given amount of time, such as requests per second.

Availablility

Availability describes the percentage of time when a server is up and running. This is usually measured in percentages or more typically nines. If a server is available 99% of the time, we say that it has 2 nines of availability. A system is highly available if it has five or more nines of availability.

Redundancy

Redundency is a means of increasing availability by having copies of the system ready to go in case the main system fails.