### [Fast Fallback](https://square.github.io/okhttp/4.x/okhttp/okhttp3/-ok-http-client/-builder/fast-fallback/)

Since version 5.0, `OkHttpClient` supports fast fallback, which is our implementation of Happy Eyeballs [RFC 6555](https://datatracker.ietf.org/doc/html/rfc6555).

fs.s3a.committer.threads=2048 # Number of threads writing to MinIO
fs.s3a.connection.maximum=8192 # Maximum number of concurrent conns
fs.s3a.fast.upload.active.blocks=2048 # Number of parallel uploads
fs.s3a.fast.upload.buffer=disk # Use disk as the buffer for uploads
fs.s3a.fast.upload=true # Turn on fast upload mode
fs.s3a.max.total.tasks=2048 # Maximum number of parallel tasks
fs.s3a.multipart.size=512M # Size of each multipart chunk

    email: ******@****.***
identifiers:
repository-code: 'https://github.com/fastapi/fastapi'
url: 'https://fastapi.tiangolo.com'
abstract: >-
  FastAPI framework, high performance, easy to learn, fast to code,
  ready for production
keywords:
  - fastapi
  - pydantic
  - starlette

Anyway, in any of the cases above, FastAPI will still work asynchronously and be extremely fast.

But by following the steps above, it will be able to do some performance optimizations.

## Technical Details { #technical-details }

---
name: Bug report
about: A reproducible problem
title: ''
labels: bug
assignees: ''

---

Good bug reports include a failing test! Writing a test helps you to isolate and describe the problem, and it helps us to fix it fast. Bug reports without a failing test or reproduction steps are likely to be closed.

Here’s an example test to get you started.

	}

	// Help provides help for config values
	Help = config.HelpKVS{
		config.HelpKV{
			Key:         Speed,
			Description: `customize scanner speed (default|slowest|slow|fast|fastest)` + defaultHelpPostfix(Speed),
			Optional:    true,
			Type:        "string",
		},
		config.HelpKV{
			Key:         ExcessVersions,

                "  <div class=\"wistia-video\"> \n" +
                "    <div class=\"wistia-player\"> \n" +
                "      <script src=\"https://fast.wistia.com/embed/medias/$2.jsonp\" async></script> \n" +
                "      <script src=\"https://fast.wistia.com/assets/external/E-v1.js\" async></script> \n" +
                "        <div class=\"wistia_responsive_padding\" style=\"padding:55.94% 0 0 0;position:relative;\"> \n" +

  // The number of elements in the replacement array.
  private final int replacementsLength;
  // The first code point in the safe range.
  private final int safeMin;
  // The last code point in the safe range.
  private final int safeMax;

  // Cropped values used in the fast path range checks.
  private final char safeMinChar;
  private final char safeMaxChar;

  /**

# FORMAT NOT DOCUMENTED YET (parser is urltestparser.js)

# Based on http://trac.webkit.org/browser/trunk/LayoutTests/fast/url/script-tests/segments.js
http://example\t.\norg http://example.org/foo/bar s:http h:example.org p:/
http://user:pass@foo:21/bar;par?b#c  s:http u:user pass:pass h:foo port:21 p:/bar;par q:?b f:#c
http:foo.com  s:http h:example.org p:/foo/foo.com
\t\s\s\s:foo.com\s\s\s\n  s:http h:example.org p:/foo/:foo.com

## Version 5.0.0-alpha.4

_2022-02-01_

**This release introduces fast fallback to better support mixed IPv4+IPv6 networks.** Fast fallback
is what we're calling our implementation of Happy Eyeballs, [RFC 8305][rfc_8305]. With this
feature OkHttp will attempt both IPv6 and IPv4 connections concurrently, keeping whichever connects
first. Fast fallback gives IPv6 connections a 250 ms head start so IPv6 is preferred on networks