It takes extremely long to extract a ZIP archive, especially if it contains many files.

This was originally raised as MDLSITE-6114 and MDLSITE-6129 where plugin developers experienced timeouts when they were submitting plugins to the Plugins directory. Moodle did not manage to extract the submitted ZIP and timed out.

Comments in MDLSITE-6129 have the whole story, the executive summary follows.

stronk7 correctly identified the bottleneck in the current implementation of zip_packer::extract_to_pathname() which iterates over all files in the archive, obtains a stream resource for each of the files, reads from the stream in 256KB blocks and writes them into the target location. ZipArchive::getStream() takes significant time in this whole chain and if there are many files (e.g. a plugin with vendor folder), the difference becomes significant.

It was suggested to switch to the alternative implementation that makes use of ZipArchive::extractTo(). That was confirmed to have significantly improved performance. During the development, a PHP bug in the ZipArchive extensions was discovered and communicated upstream.

This issue brings a new version of the method which works significantly faster than the previous implementation and has work around for the said upstream PHP bug.