add dsnitch comments
Project: http://git-wip-us.apache.org/repos/asf/cassandra/repo Commit: http://git-wip-us.apache.org/repos/asf/cassandra/commit/acc3c8de Tree: http://git-wip-us.apache.org/repos/asf/cassandra/tree/acc3c8de Diff: http://git-wip-us.apache.org/repos/asf/cassandra/diff/acc3c8de Branch: refs/heads/trunk Commit: acc3c8de29b4d8826e45fc5dd956a67205a0b369 Parents: 295d6af Author: Brandon Williams <[email protected]> Authored: Tue Feb 5 13:50:59 2013 -0600 Committer: Brandon Williams <[email protected]> Committed: Tue Feb 5 13:50:59 2013 -0600 ---------------------------------------------------------------------- .../cassandra/locator/DynamicEndpointSnitch.java | 7 +++++++ 1 files changed, 7 insertions(+), 0 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/cassandra/blob/acc3c8de/src/java/org/apache/cassandra/locator/DynamicEndpointSnitch.java ---------------------------------------------------------------------- diff --git a/src/java/org/apache/cassandra/locator/DynamicEndpointSnitch.java b/src/java/org/apache/cassandra/locator/DynamicEndpointSnitch.java index 40aad20..214208e 100644 --- a/src/java/org/apache/cassandra/locator/DynamicEndpointSnitch.java +++ b/src/java/org/apache/cassandra/locator/DynamicEndpointSnitch.java @@ -230,6 +230,8 @@ public class DynamicEndpointSnitch extends AbstractEndpointSnitch implements ILa double maxLatency = 1; long maxPenalty = 1; HashMap<InetAddress, Long> penalties = new HashMap<InetAddress, Long>(); + // We're going to weight the latency and time since last reply for each host against the worst one we see, to arrive at sort of a 'badness percentage' for both of them. + // first, find the worst for each. for (Map.Entry<InetAddress, ExponentiallyDecayingSample> entry : samples.entrySet()) { double mean = entry.getValue().getSnapshot().getMedian(); @@ -238,18 +240,23 @@ public class DynamicEndpointSnitch extends AbstractEndpointSnitch implements ILa long timePenalty = lastReceived.containsKey(entry.getKey()) ? lastReceived.get(entry.getKey()) : System.currentTimeMillis(); timePenalty = System.currentTimeMillis() - timePenalty; timePenalty = timePenalty > UPDATE_INTERVAL_IN_MS ? UPDATE_INTERVAL_IN_MS : timePenalty; + // a convenient place to remember this since we've already calculated it and need it later penalties.put(entry.getKey(), timePenalty); if (timePenalty > maxPenalty) maxPenalty = timePenalty; } + // now make another pass to do the weighting based on the maximums we found before for (Map.Entry<InetAddress, ExponentiallyDecayingSample> entry: samples.entrySet()) { double score = entry.getValue().getSnapshot().getMedian() / maxLatency; if (penalties.containsKey(entry.getKey())) score += penalties.get(entry.getKey()) / ((double) maxPenalty); else + // there's a chance a host was added to the samples after our previous loop to get the time penalties. Add 1.0 to it, or '100% bad' for the time penalty. score += 1; // maxPenalty / maxPenalty + // finally, add the severity without any weighting, since hosts scale this relative to their own load and the size of the task causing the severity score += StorageService.instance.getSeverity(entry.getKey()); + // lowest score (least amount of badness) wins. scores.put(entry.getKey(), score); } }
