curl/docs/PARALLEL-TRANSFERS.md
Daniel Stenberg 86d33001e4
reuse: add copyright + license info to individual docs/*.md files
Instead of use 'docs/*.md' in dep5. For clarity and avoiding a wide-
matching wildcard.

+ Remove mention of old files from .reuse/dep5
+ add info to .github/dependabot.yml
+ make scripts/copyright.pl warn on non-matching patterns

Closes #13245
2024-03-31 12:01:18 +02:00

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<!--
Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
-->
# Parallel transfers
curl 7.66.0 introduced support for doing multiple transfers simultaneously; in
parallel.
## -Z, --parallel
When this command line option is used, curl performs the transfers given to it
at the same time. It does up to `--parallel-max` concurrent transfers, with a
default value of 50.
## Progress meter
The progress meter that is displayed when doing parallel transfers is
completely different than the regular one used for each single transfer.
It shows:
o percent download (if known, which means *all* transfers need to have a
known size)
o percent upload (if known, with the same caveat as for download)
o total amount of downloaded data
o total amount of uploaded data
o number of transfers to perform
o number of concurrent transfers being transferred right now
o number of transfers queued up waiting to start
o total time all transfers are expected to take (if sizes are known)
o current time the transfers have spent so far
o estimated time left (if sizes are known)
o current transfer speed (the faster of upload/download speeds measured over
the last few seconds)
Example:
DL% UL% Dled Uled Xfers Live Qd Total Current Left Speed
72 -- 37.9G 0 101 30 23 0:00:55 0:00:34 0:00:22 2752M
## Behavior differences
Connections are shared fine between different easy handles, but the
"authentication contexts" are not. For example doing HTTP Digest auth with one
handle for a particular transfer and then continue on with another handle that
reuses the same connection, the second handle cannot send the necessary
Authorization header at once since the context is only kept in the original
easy handle.
To fix this, the authorization state could be made possible to share with the
share API as well, as a context per origin + path (realm?) basically.
Visible in test 153, 1412 and more.