added context check in iterativeLookup, solves cache contention issue #407
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Resolves #404
Description
More details in #404, but in short
mainsaw ZDNS slow to a crawl andpproftrace of goroutines showed most were waiting on a cache shard lock. I usedgit bisectto find the first bad version and it fortunately wasn't the large CLI + library split PR (c192044) but a much smaller commit's change-set.Turned out, the first bad version was 67026d, where I tried to improve timeout handling. Specifically, here where I removed the timeout check in
cachedRetryingLookup. I believe what was happening was that as long as we never went to the wire (where we do check the context again)but stayed just hitting the cache, this execution loop would never time out and the thread would be stuck:By adding a check on the context in
iterativeLookup, we can break the cycle.Testing
Command -
head -n 7000 10k_crux.input | ./zdns A --iterative --threads=100 --timeout=20 --iteration-timeout=20 --output-file="out.logTime to Crawl 7k Domains
v1.1.0: - 1 min. 50 sec.main: - > 10 mins, gave up at this point. There were 50/7k domains yet to be resolvede5e2d8- This PR: - 1 min 26 secs