commit 42cf030d06171ec1f595da24b7cec3648f64b002
author Youssef Elghareeb <ghareeb@google.com> Mon Jun 21 12:55:12 2021 +0200
committer Youssef Elghareeb <ghareeb@google.com> Mon Jun 21 18:44:26 2021 +0200
tree 09709d05deda8869693c0ae327ab994d50867594
parent 07a931b3fd706648b81300d17deb127bbd5419f9

Use faster fallback diff algorithm in case of timeouts

Current logic uses the default diff algorithm "Histogram Diff". In case
of timeouts, it throws an exception that is propagated to the caller.

In this change, we adjust the logic to follow what was implemented in
PatchListLoader (the old diff cache): If the diff execution times out,
we fallback to the faster histogram algorithm without myers diff and log
a warning message. Notice that in DiffOperations, the fallback is done
outside the cache, i.e. we are requesting the diff from the cache with
new keys that specify which algorithm should be used. In old diff cache,
this fallback was done inside the cache loader. This is one of the
advantages of the new diff cache that we can explicitly specify which
algorithm to use as part of the cache key.

This change implies that slow requests will always have to go through
the timeout before requesting the diffs using the faster algorithm. In a
follow up change, we can enhance the logic by caching negative results
for the histogram diff keys to quickly fallback without having to
hit the timeout.

Change-Id: I34fe29dc166534d835c97beab85661facafac31f