txfib

Inspired by https://github.com/glenjamin/node-fib

Considered Approaches

Here’s approaches presented in `txfib` for running a long CPU/memory intensive operation:

• in separate threads (with a thread pool); e.g., `recfib()`
• in separate processes (without a process pool); e.g., `binetfib_exact()`
• in a reactor thread
  • blocking the event-loop for a long time; e.g., `binetfib()`
  • non-blocking (cooperatively i.e., blocking for a short time); e.g., `iterfib()`, `sicpfib()`, `memfib()`

iterfib

O(n) steps, O(n) in memory (to hold the result) simple iterative non-blocking

sicpfib

O(log(n)) steps, O(n) in memory based on finding power of 2x2 matrix

binetfib_exact

O(1) bigdecimal steps, O(n) in memory in a process Binet’s formula; precision depends on n

binetfib

O(1) steps, O(1) memory in the reactor thread the same but with fixed precision

memfib

recursive formula with limited memoization running in the reactor thread cooperatively

recfib

O(a**n) steps, O(a**n) memory in a thread recursive formula without memoization

nth fibonacci number has O(n) digits so each step is O(n) operation by itself (except `binetfib()` that produces inexact results).

Usage

$ pip install twisted
$ twistd -ny fibonacci.py

Optionally you could install psutil to enable reporting CPU/memory usage of the process.

Open http://localhost:1597/ in browser

Performance

`/sicpfib/100` is ~2 times worse when node-fib on `ab`:

$ ab -n 10000 -c 50 'http://127.0.0.1:1597/sicpfib/100'
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/
Benchmarking 127.0.0.1 (be patient)
Server Software: TwistedWeb/10.2.0
Server Hostname: 127.0.0.1
Server Port: 1597
Document Path: /sicpfib/100
Document Length: 21 bytes
Concurrency Level: 50
Time taken for tests: 4.442 seconds
Complete requests: 10000
Failed requests: 0
Write errors: 0
Total transferred: 1290000 bytes
HTML transferred: 210000 bytes
Requests per second: 2251.45 [#/sec] (mean)
Time per request: 22.208 [ms] (mean)
Time per request: 0.444 [ms] (mean, across all concurrent requests)
Transfer rate: 283.63 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 0 0.1 0 2
Processing: 18 22 1.4 22 34
Waiting: 18 22 1.4 22 34
Total: 19 22 1.5 22 34
Percentage of the requests served within a certain time (ms)
50% 22
66% 22
75% 22
80% 23
90% 23
95% 24
98% 28
99% 29
100% 34 (longest request)