vjagadish1989 commented on a change in pull request #952: Improved
standby-aware container allocation for active-containers on job redeploys
URL: https://github.com/apache/samza/pull/952#discussion_r267635366
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File path:
samza-core/src/main/java/org/apache/samza/clustermanager/StandbyContainerManager.java
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@@ -161,54 +161,72 @@ private void handleStandbyContainerStop(String
standbyContainerID, String resour
}
}
- /** Method to handle failover for an active container.
- * We try to find a standby for the active container, and issue a stop on
it.
- * If we do not find a standby container, we simply issue an anyhost
request to place it.
+ /** Method to handle standby-aware allocation for an active container.
+ * We try to find a standby host for the active container, and issue a stop
on any standby-containers running on it,
+ * request resource to place the active on the standby's host, and one to
place the standby elsewhere.
*
- * @param containerID the samzaContainerID of the active-container
+ * @param activeContainerID the samzaContainerID of the active-container
* @param resourceID the samza-resource-ID of the container when it failed
(used to index failover-state)
*/
- private void initiateActiveContainerFailover(String containerID, String
resourceID,
+ private void initiateStandbyAwareAllocation(String activeContainerID, String
resourceID,
AbstractContainerAllocator containerAllocator) {
- Optional<Entry<String, SamzaResource>> standbyContainer =
this.selectStandby(containerID, resourceID);
+ String standbyHost = this.selectStandbyHost(activeContainerID, resourceID);
- // If we find a standbyContainer, we initiate a failover
- if (standbyContainer.isPresent()) {
+ // Check if there is a running standby-container on that host that needs
to be stopped
+ List<String> standbyContainers =
this.standbyContainerConstraints.get(activeContainerID);
+ Map<String, SamzaResource> runningStandbyContainersOnHost =
this.samzaApplicationState.runningContainers.entrySet().stream().filter(x ->
standbyContainers.contains(x.getKey()))
+ .filter(x ->
x.getValue().getHost().equals(standbyHost)).collect(Collectors.toMap(Map.Entry::getKey,
Map.Entry::getValue));
- String standbyContainerId = standbyContainer.get().getKey();
- SamzaResource standbyResource = standbyContainer.get().getValue();
- String standbyResourceID = standbyResource.getResourceID();
- String standbyHost = standbyResource.getHost();
+ // if the standbyHost returned is anyhost, we proceed with the request
directly
Review comment:
As a readability guideline, `If...Else-if..Else` blocks should check
predicates which are related. For eg: it may not be obvious that standbyHost ==
ANY_HOST and runningStandbyContainersOnHost.isEmpty are related..
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