Problem/Motivation
unserialize is slow. Even though the cache items are stored in PHP files unserialization is still slow. Opcache does not much help in this case.
On Drupal sites served from Page Cache, loading the container from the cache backend is one of the most expensive operations in terms of its percentage of the total request time.
Proposed resolution
Use symfony/var-exporter for exporting cached data.
It claims to be much faster than unserialize()
The reason to use VarExporter::export() vs serialize() or igbinary is performance: thanks to OPcache, the resulting code is significantly faster and more memory efficient than using unserialize() or igbinary_unserialize().