This commit renames the 'queue_json_publish' function to
'queue_json_publish_rollback_unsafe' to reflect the fact that it doesn't
wait for the db transaction (within which it gets called, if any)
to commit and sends event irrespective of commit or rollback.
In most of the cases we don't want to send event in the case of
rollbacks, so the caller should be aware that calling the function
directly is rollback unsafe.
Fixes part of #30489.
SIGALRM is the simplest way to set a specific maximum duration that
queue workers can take to handle a specific message. This only works
in non-threaded environments, however, as signal handlers are
per-process, not per-thread.
The MAX_CONSUME_SECONDS is set quite high, at 10s -- the longest
average worker consume time is embed_links, which hovers near 1s.
Since just knowing the recent mean does not give much information[1],
it is difficult to know how much variance is expected. As such, we
set the threshold to be such that only events which are significant
outliers will be timed out. This can be tuned downwards as more
statistics are gathered on the runtime of the workers.
The exception to this is DeferredWorker, which deals with quite-long
requests, and thus has no enforceable SLO.
[1] https://www.autodesk.com/research/publications/same-stats-different-graphs
