repo-add takes one package at a time: it hashes the archive and lists its
files, which means decompressing all of it, for about a thousand
packages one after another.
A database is a tar of one directory per package. The packages are dealt
out to one repo-add per CPU, each writing its own database, and the
pieces are joined. On 160 packages on a 16-core machine the result is
identical to one repo-add's, db and files, in 1.0 s against 6.3 s. Two
versions of one package name are an error: one repo-add would keep the
last, the pieces apart would keep both.
Emir Beganovic
ebfbf43aa0