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new 41ea8b9 [Docs][LoadBalancing] Add/Improve Javadocs for
LoadSheddingStrategy impls (#12180)
41ea8b9 is described below
commit 41ea8b9924df442b934fed90391c43ddb45e9996
Author: Michael Marshall <[email protected]>
AuthorDate: Tue Sep 28 19:38:04 2021 -0500
[Docs][LoadBalancing] Add/Improve Javadocs for LoadSheddingStrategy impls
(#12180)
* [LoadBalancing] Add/Improve Javadocs for LoadSheddingStrategy impls
* Use present tense
Co-authored-by: Anonymitaet <[email protected]>
Co-authored-by: Anonymitaet <[email protected]>
---
.../pulsar/broker/loadbalance/impl/OverloadShedder.java | 11 +++++++----
.../pulsar/broker/loadbalance/impl/ThresholdShedder.java | 12 ++++++++++++
2 files changed, 19 insertions(+), 4 deletions(-)
diff --git
a/pulsar-broker/src/main/java/org/apache/pulsar/broker/loadbalance/impl/OverloadShedder.java
b/pulsar-broker/src/main/java/org/apache/pulsar/broker/loadbalance/impl/OverloadShedder.java
index 89e3204..67e10dc 100644
---
a/pulsar-broker/src/main/java/org/apache/pulsar/broker/loadbalance/impl/OverloadShedder.java
+++
b/pulsar-broker/src/main/java/org/apache/pulsar/broker/loadbalance/impl/OverloadShedder.java
@@ -35,11 +35,14 @@ import org.slf4j.LoggerFactory;
/**
* Load shedding strategy which will attempt to shed exactly one bundle on
brokers which are overloaded, that is, whose
- * maximum system resource usage exceeds
loadBalancerBrokerOverloadedThresholdPercentage. A bundle will be recommended
- * for unloading off that broker if and only if the following conditions hold:
The broker has at least two bundles
- * assigned and the broker has at least one bundle that has not been unloaded
recently according to
+ * maximum system resource usage exceeds
loadBalancerBrokerOverloadedThresholdPercentage. To see which resources are
+ * considered when determining the maximum system resource, see {@link
LocalBrokerData#getMaxResourceUsage()}. A bundle
+ * is recommended for unloading off that broker if and only if the following
conditions hold: The broker has at
+ * least two bundles assigned and the broker has at least one bundle that has
not been unloaded recently according to
* LoadBalancerSheddingGracePeriodMinutes. The unloaded bundle will be the
most expensive bundle in terms of message
- * rate that has not been recently unloaded.
+ * rate that has not been recently unloaded. Note that this strategy does not
take into account "underloaded" brokers
+ * when determining which bundles to unload. If you are looking for a strategy
that spreads load evenly across
+ * all brokers, see {@link ThresholdShedder}.
*/
public class OverloadShedder implements LoadSheddingStrategy {
diff --git
a/pulsar-broker/src/main/java/org/apache/pulsar/broker/loadbalance/impl/ThresholdShedder.java
b/pulsar-broker/src/main/java/org/apache/pulsar/broker/loadbalance/impl/ThresholdShedder.java
index f33ad9c..a8e6edf 100644
---
a/pulsar-broker/src/main/java/org/apache/pulsar/broker/loadbalance/impl/ThresholdShedder.java
+++
b/pulsar-broker/src/main/java/org/apache/pulsar/broker/loadbalance/impl/ThresholdShedder.java
@@ -35,6 +35,18 @@ import
org.apache.pulsar.policies.data.loadbalancer.LocalBrokerData;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
+/**
+ * Load shedding strategy that unloads any broker that exceeds the average
resource utilization of all brokers by a
+ * configured threshold. As a consequence, this strategy tends to distribute
load among all brokers. It does this by
+ * first computing the average resource usage per broker for the whole
cluster. The resource usage for each broker is
+ * calculated using the following method: {@link
LocalBrokerData#getMaxResourceUsageWithWeight)}. The weights for each
+ * resource are configurable. Historical observations are included in the
running average based on the broker's
+ * setting for loadBalancerHistoryResourcePercentage. Once the average
resource usage is calculated, a broker's
+ * current/historical usage is compared to the average broker usage. If a
broker's usage is greater than the average
+ * usage per broker plus the loadBalancerBrokerThresholdShedderPercentage,
this load shedder proposes removing
+ * enough bundles to bring the unloaded broker 5% below the current average
broker usage. Note that recently
+ * unloaded bundles are not unloaded again.
+ */
public class ThresholdShedder implements LoadSheddingStrategy {
private static final Logger log =
LoggerFactory.getLogger(ThresholdShedder.class);
