programming
General programming knowledge, useful tidbits and parts to pick up along the way.
Latency comparison numbers
Latency Comparison Numbers
| Operation | Time | Comparison (L1 cache reference = 1 second) | |
|---|---|---|---|
| L1 cache reference | 0.5 ns | 0:00:01 | |
| Branch mispredict | 5 ns | 0:00:10 | |
| L2 cache reference | 7 ns | 0:00:14 | |
| Mutex lock/unlock | 25 ns | 0:00:50 | |
| Main memory reference | 100 ns | 0:03:20 | |
| Compress 1K bytes with Zippy | 3,000 ns | 1:40:00 | |
| Send 1K bytes over 1 Gbps network | 10,000 ns ~= 0.01 ms | 5:33:20 | |
| Read 4K randomly from SSD* | 150,000 ns ~= 0.15 ms | 3 days, 11:20:00 | |
| Read 1 MB sequentially from memory | 250,000 ns ~= 0.25 ms | 5 days, 18:53:20 | |
| Round trip within same data center | 500,000 ns ~= 0.5 ms | 11 days, 13:46:40 | |
| Read 1 MB sequentially from SSD* | 1,000,000 ns ~= 1 ms | 23 days, 3:33:20 | |
| Disk seek | 10,000,000 ns ~= 10 ms | 231 days, 11:33:20 | |
| Read 1 MB sequentially from disk | 20,000,000 ns ~= 20 ms | 462 days, 23:06:40 | |
| Send packet CA->Netherlands->CA | 150,000,000 ns ~= 150 ms | 3472 days, 5:20:00 |
Notes
- 1 ns = 10-9 seconds
- 1 ms = 10-3 seconds
- Assuming ~1GB/sec SSD
See Also
- Numbers Every Programmer Should Know
- By Jeff Dean: http://research.google.com/people/jeff/
- Originally by Peter Norvig: http://norvig.com/21-days.html#answers
- https://gist.github.com/jboner/2841832
Meta programming
Programming on a higher level; not bound by languages.
Debugging
There's only so much humans can do to prevent bugs. Languages like rust are
appealing because once you get them running they will not crash. These are some
methods humans can use to find out why computers aren't doing what you ought
them to do.
- triage (printing)
- disinfect (linting)
- monitor (logging)
- traces (stack traces)
- test (test cases)
- scan (???)
- probe (dynamic tracing in dynamic langs)
- observe (direct interaction)
- intervene (built-in debugger)
- operate (inspector tooling)
- biopsy (resource leaks)
postmortem (gdb / lldb)