Comment 150 for bug 363695

The suggested fix and the currently applied fix differ in one important aspect: The --update option has been dropped.

tldr: Unless --update is broken (and it doesn't appear to be), it should be included in the fix as it reduces run time quite significantly.

To estimate the effect of --update I tried installing a number of small apps (e.g. htop) and running the command: update-apt-xapian-index --update (with default niceness). The time required to perform this update varied from about 40 seconds to almost 3 times that. The update process appears to be split into three main components:

- Reading translations for all ubuntu repos in use (security_universe, updates_restricted, main, universe, partner, multiverse, etc).
- Reading xapian index.
- Updating xapian index.

When a complete rebuild is performed, the index doesn't need to be read (and isn't).

In terms of time, the first and second steps are fairly constant, while the updating bit varies wildly with no pattern I was able to determine (from about 10 to 60 seconds).

Reading the index was quick, about 5 seconds.

The translations part, which I assume is basically fetching complete descriptions of all packages installed, is rather slow even on a fast internet connection. On my system, it took a consistent 25 seconds.

Without debating the merits of the index and its use, there are certainly a number of optimizations that could be made. Even without touching the process itself, just using the incremental update feature cuts run time significantly with no apparent downside.