A few commits ago, we bumped up the default zstandard compression level
from 3 to 10 when we switched to multi-threaded compression. Even with
multiple threads, this was a bit slower.
For images that will be built once and read multiple times, it is
worthwhile to burn extra CPU once and produce a small image. However,
for other tasks where the number of reads is limited, it isn't
worth it to use this extra CPU. This commit uses the SCM level as
a proxy for "optimize for speed." If the task is associated with level
1 (a try push), we lower the compression level and optimize for
speed. Otherwise, we keep the higher compression level and
optimize for image size.
Credit goes to Jonas for this terrific idea.
MozReview-Commit-ID: Hui97KsZpgw
Note that the to_json method prefers the taskgraph's dependencies information
(edges) to that from the task.dependencies entries. At a few points in
task-graph generation, these values differ, although that is expected (for
example, the full task set contains no edges, but that information is still in
task.dependencies). Unifying that representation leads to some difficulty with
task transforms that reach into the dependency tree (beetmover), so the
different representations are left as-is.
MozReview-Commit-ID: GeW8HNwFA9Z
