Calculation
Define estimate numbers:
- #users
- #operations/events
- data size per op/event
General formulas:
Number of operations per day
[# of operations / day] = [# of DAU] * [# of operations per 1 user]
unit: #(ops)/day | e.g.: 1M(ops)/dayNumber of data generated/transferred per day
[# of data / day] = [# of ops / day] * [size of data per 1 op]
unit: storage_unit/day | e.g.: 1MB/dayDay to second conversion
1 day = 86400 sQPS estimate
[# of query ops / second] = [# query ops / day] / 86400
unit: #(ops)/s | e.g.: 1M(queries)/sThroughput estimate
[# of data / second] = [# data transferred / day] / 86400
unit: storage_unit/s | e.g.: 1MB/sMust Know Terms:
DAU (Daily Active Users)
- total number of users that engage in some way with a web or mobile product on a given day
Bandwidth
- maximum amount of data that can travel through a ‘channel’
Throughput
- amount of data actually does travel through the ‘channel’ successfully.
- number of actions executed or results produced per unit of time.
- e.g.
actions/second
Latency
- time required to perform some action or to produce some result.
- measured in units of time – hours, minutes, seconds, nanoseconds or clock periods.
- e.g.
seconds/action
QPS
- Queries per second
- number of query operations / second
Product Numbers
Engineering Numbers
1 word = 2 bytes = 16 bits (common)
1 byte = 8 bits
1 int (java) = 4 bytes => -2,147,483,648 to 2,147,483,647
1 long (java) = 8 bytes => -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
1 KB = 1024 B
1 MB = 1024 KB
1 GB = 1024 MB
1 TB = 1024 GB
1 PB = 1024 TB
Powers of two table
| Power | Exact Value | Approx Value | Bytes |
|---|---|---|---|
| 0 | 1 | 1B | |
| 7 | 128 | ||
| 8 | 256 | ||
| 10 | 1024 | 1 thousand | 1 KB |
| 16 | 65,536 | 64 KB | |
| 20 | 1,048,576 | 1 million | 1 MB |
| 30 | 1,073,741,824 | 1 billion | 1 GB |
| 32 | 4,294,967,296 | 4 GB | |
| 40 | 1,099,511,627,776 | 1 trillion | 1 TB |
Source(s) and further reading
Latency numbers every programmer should know
| Latency Comparison Numbers | ||||
|---|---|---|---|---|
| L1 cache reference | 0.5 ns | |||
| Branch mispredict | 5 ns | |||
| L2 cache reference | 7 ns | 14x L1 cache | ||
| Mutex lock/unlock | 25 ns | |||
| Main memory reference | 100 ns | 20x L2 cache, 200x L1 cache | ||
| Compress 1K bytes with Zippy | 10,000 ns | 10 us | ||
| Send 1 KB bytes over 1 Gbps network | 10,000 ns | 10 us | ||
| Read 4 KB randomly from SSD* | 150,000 ns | 150 us | ~1GB/sec SSD | |
| Read 1 MB sequentially from memory | 250,000 ns | 250 us | ||
| Round trip within same datacenter | 500,000 ns | 500 us | ||
| Read 1 MB sequentially from SSD* | 1,000,000 ns | 1,000 us | 1 ms | ~1GB/sec SSD, 4X memory |
| Disk seek | 10,000,000 ns | 10,000 us | 10 ms | 20x datacenter roundtrip |
| Read 1 MB sequentially from 1 Gbps | 10,000,000 ns | 10,000 us | 10 ms | 40x memory, 10X SSD |
| Read 1 MB sequentially from disk | 30,000,000 ns | 30,000 us | 30 ms | 120x memory, 30X SSD |
| Send packet CA->Netherlands->CA | 150,000,000 ns | 150,000 us | 150 ms |
Notes
1 ns = 10^-9 seconds
1 us = 10^-6 seconds = 1,000 ns
1 ms = 10^-3 seconds = 1,000 us = 1,000,000 ns
Handy metrics based on numbers above:
- Read sequentially from disk at 30 MB/s
- Read sequentially from 1 Gbps Ethernet at 100 MB/s
- Read sequentially from SSD at 1 GB/s
- Read sequentially from main memory at 4 GB/s
- 6-7 world-wide round trips per second
- 2,000 round trips per second within a data center
