TYPO3 Core

I just realized that php-redis in Ubuntu 18.04 has a dependency on php-igbinary.
This made me wonder because I remember it was used in the past in the caching framework but got removed again later:

- https://forge.typo3.org/issues/74501
- https://review.typo3.org/c/Packages/TYPO3.CMS/+/47157

The changelog for the removal commit says:

[TASK] Remove igbinary from cache framework

The patch removes igbinary serializer support from the cache framework.
When igbinary support was added back then in PHP 5.3 times, it had the
potential to serialize data quicker than the default serializer.

Unfortunately, other promises aren't held:
* The module found no general acceptance within the PHP community and
  isn't supported very well. PHP 7 is still not officially supported.
* Last release at the time of this writing was in 2014-08
* The module must still be compiled from source and no recent
  distribution ever packaged it by default
* The maintenance load on devOps side is high: The module must be
  recompiled with each minor php release
* In case the module is not updated, it throws errors at a central place
  of the system and can easily brick a whole instance
* The module found no huge acceptance by hosters and is only very rarely
  used in real life instances
* A performance impact is only measurable in very small and highly
  specialized use cases, it typically plays no role in casual frontend
  or backend requests.

We've seen several life systems in the wild lately with sloppy hosters
not maintaining the igbinary module within their infrastructure properly.
The current implementation with VariableFrontend dynamically detecting
and then force using the module leads to hard crashes in those situations.
The main issue is that serializing is done via PHPs serializer and
unserializing using igbinary then fails, effectively rendering the
entire installation bricked.
To come by those situations, it is considered more important to deliver
a stable product than a product that is quicker in more theoretical use
cases.

Thus, the support for this module is kicked from the standard cache
frontend. In case igbinary still gives significant boost for specialized
specific instances, an admin can still configure a VariableFrontend that
uses this serializer.

As it looks to me, this is no longer valid, and the module is actively improved:

- https://pecl.php.net/package/redis
- https://pecl.php.net/package-changelog.php?package=redis

Also, it is now required by php-redis:

- https://github.com/phpredis/phpredis/commit/3baccddd11e4c8526f46884d73c44a63b02ecf6f
- see changelog above at version 3.1.1
- Ubuntu 18.04 package: https://launchpad.net/ubuntu/bionic/+source/php-redis

Therefore I suggest to check again if the situation has changed and if php-igbinary support should be added (with a configuration flag?) again.