[masklinn]

> Could someone more versed with PHP, and this project explain why turning off garbage collection helped so much?

The cycle collector is relatively recent, I expect it's not very performant (since most PHP applications don't need it) and composer's dependency resolution may be hitting a pathological case (create lots of objects without cycles, triggering lots of collections but no actually useful work)

> and why they didn't turn it back on at the end of the function?

Since it's a package manager, I'd guess the expectation is the process will die soon-ish afterwards (once it's installed whatever it's resolved). There's a discussion of re-enabling it after dependency resolution (so postinstall hooks run with GC enabled) though.