rate-limiting: propagate back-pressure from queue as HTTP 429's #179
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yaauie
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| final boolean isCompact = execution.markComplete(); | ||
| if (!isCompact) { | ||
| this.compactTail(); | ||
| } |
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review note:
The Execution#markComplete() returns true iff marking the execution complete resulted in a node-level compaction. If it didn't, we try to compact from the tail.
| if (preCompletionNext != null) { | ||
| final Execution newNext = preCompletionNext.chaseTail(); | ||
| return (newNext != preCompletionNext) && NEXT.compareAndSet(this, preCompletionNext, newNext); | ||
| } |
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We can't actually compact the completed node out, since we don't have a reference to its prev and a doubly-linked list is more complex than we need.
But we can fast-forward a newly-completed node's next pointer to the first node in the sequence that is either not yet completed or has no next, which may be a compaction that frees up memory and reduces future computation.
When we succeed at compacting, we return true so that the caller can make decisions about performing additional compactions.
| private static final java.lang.invoke.VarHandle NEXT; | ||
| static { | ||
| try { | ||
| MethodHandles.Lookup l = MethodHandles.lookup(); | ||
| NEXT = l.findVarHandle(Execution.class, "next", Execution.class); | ||
| } catch (ReflectiveOperationException e) { | ||
| throw new ExceptionInInitializerError(e); | ||
| } | ||
| } |
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oops, this is Java 9+, so we would need to guard against it being installed in Logstash 7 (or rework to use AtomicReferences)
| private final AtomicReference<Execution> head; // newest execution | ||
| private final AtomicReference<Execution> tail; // oldest execution |
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TODO: invert to match java semantics, where things go into the tail (back) of a queue and are removed from the head (front)
Adds a proactive handler that rejects new requests with HTTP 429's when the queue has been blocking for more than 10 consecutive seconds, allowing back- pressure to propagate in advance of filling up the connection backlog queue.
yaauie
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Adds a proactive handler that rejects new requests with HTTP 429's when the queue has been blocking for more than 10 consecutive seconds, allowing back- pressure to propagate in advance of filling up the connection backlog queue.
While I'd like to take the time to break out the supplied
ExecutionObserverinto a separate library, I think it is better to roll with what we have than to hold back.