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Prohibit assigning concurrent maps into Map-typed variables and fields and fix a race condition in CoordinatorRuleManager #6898
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101ca9c
Prohibit assigning concurrent maps into Map-types variables and field…
leventov 0dc1659
Enforce that if compute(), computeIfAbsent(), computeIfPresent() or m…
leventov 19056c1
Remove unnecessary comment
leventov 2791d9f
Checkstyle
leventov 5071ea0
Merge remote-tracking branch 'upstream/master' into concurrent-map-type
leventov 9d48d18
Fix getFromExtensions()
leventov 14307c3
Add a reference to the comment about guarded computeIfAbsent() optimi…
leventov e363b01
Fix UriCacheGeneratorTest
leventov cd472a1
Workaround issue with MaterializedViewQueryQueryToolChest
leventov 4bb8a7a
Strengthen Appenderator's contract regarding concurrency
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Any idea why ConcurrentHashMap does not already employ an optimization like this?
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That's a throughput vs. scalability tradeoff, + lack of information. We are potentially doing two operations instead of one, and avoid locking in some cases instead.
At some sites where
computeIfAbsent()
is actually expected to find the key absent and compute the value most of the time, theget()
guard just makes things worse.There is also an area where it's hard for me to say what approach is better, is that when the map is big and
computeIfAbsent()
constitutes significant part of the app's CPU consumption (the bigger the map and the hottercomputeIfAbsent()
call is, the more likely that it's better to not guardcomputeIfAbsent()
withget()
). I think it's never nearly the case on Druid nodes thatcomputeIfAbsent()
is hot, but I could be wrong.There was a problem hiding this comment.
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From the ConcurrentHashMap's part, it would be useful if
computeIfAbsentMoreScalableButMaybeDoingExtraWork()
existed, where they don't recompute hash bucket twice and just walk the collision chain twice. But it's easy to imagine why such method doesn't exist.