cameronlee314 commented on a change in pull request #1027: SAMZA-2046:
Startpoint fan out implementation
URL: https://github.com/apache/samza/pull/1027#discussion_r283536034
##########
File path:
samza-core/src/main/java/org/apache/samza/startpoint/StartpointManager.java
##########
@@ -173,71 +226,151 @@ public void deleteStartpoint(SystemStreamPartition ssp,
TaskName taskName) {
Preconditions.checkState(!stopped, "Underlying metadata store not
available");
Preconditions.checkNotNull(ssp, "SystemStreamPartition cannot be null");
- metadataStore.delete(toStoreKey(ssp, taskName));
+ readWriteStore.delete(toReadWriteStoreKey(ssp, taskName));
}
/**
- * For {@link Startpoint}s keyed only by {@link SystemStreamPartition}, this
method re-maps the Startpoints from
- * SystemStreamPartition to SystemStreamPartition+{@link TaskName} for all
tasks provided by the {@link JobModel}
+ * The Startpoints that are written to with {@link
#writeStartpoint(SystemStreamPartition, Startpoint)} and with
+ * {@link #writeStartpoint(SystemStreamPartition, TaskName, Startpoint)} are
moved from a "read-write" namespace
+ * to a "fan out" namespace.
* This method is not atomic or thread-safe. The intent is for the Samza
Processor's coordinator to use this
* method to assign the Startpoints to the appropriate tasks.
- * @param jobModel The {@link JobModel} is used to determine which {@link
TaskName} each {@link SystemStreamPartition} maps to.
- * @return The list of {@link SystemStreamPartition}s that were fanned out
to SystemStreamPartition+TaskName.
+ * @param taskToSSPs Determines which {@link TaskName} each {@link
SystemStreamPartition} maps to.
+ * @return The set of active {@link TaskName}s that were fanned out to.
*/
- public Set<SystemStreamPartition> fanOutStartpointsToTasks(JobModel
jobModel) {
+ public Set<TaskName> fanOut(Map<TaskName, Set<SystemStreamPartition>>
taskToSSPs) {
Preconditions.checkState(!stopped, "Underlying metadata store not
available");
- Preconditions.checkNotNull(jobModel, "JobModel cannot be null");
-
- HashSet<SystemStreamPartition> sspsToDelete = new HashSet<>();
-
- // Inspect the job model for TaskName-to-SSPs mapping and re-map
startpoints from SSP-only keys to SSP+TaskName keys.
- for (ContainerModel containerModel: jobModel.getContainers().values()) {
- for (TaskModel taskModel : containerModel.getTasks().values()) {
- TaskName taskName = taskModel.getTaskName();
- for (SystemStreamPartition ssp :
taskModel.getSystemStreamPartitions()) {
- Startpoint startpoint = readStartpoint(ssp); // Read SSP-only key
- if (startpoint == null) {
- LOG.debug("No Startpoint for SSP: {} in task: {}", ssp, taskName);
- continue;
- }
-
- LOG.info("Grouping Startpoint keyed on SSP: {} to tasks determined
by the job model.", ssp);
- Startpoint startpointForTask = readStartpoint(ssp, taskName);
- if (startpointForTask == null ||
startpointForTask.getCreationTimestamp() < startpoint.getCreationTimestamp()) {
- writeStartpoint(ssp, taskName, startpoint);
- sspsToDelete.add(ssp); // Mark for deletion
- LOG.info("Startpoint for SSP: {} remapped with task: {}.", ssp,
taskName);
- } else {
- LOG.info("Startpoint for SSP: {} and task: {} already exists and
will not be overwritten.", ssp, taskName);
- }
+ Preconditions.checkArgument(MapUtils.isNotEmpty(taskToSSPs), "taskToSSPs
cannot be null or empty");
+
+ // construct fan out with the existing readWriteStore entries and mark the
entries for deletion after fan out
+ Instant now = Instant.now();
+ HashMultimap<SystemStreamPartition, TaskName> deleteKeys =
HashMultimap.create();
+ HashMap<TaskName, StartpointFanOut> fanOuts = new HashMap<>();
+ for (TaskName taskName : taskToSSPs.keySet()) {
+ Set<SystemStreamPartition> ssps = taskToSSPs.get(taskName);
+ if (CollectionUtils.isEmpty(ssps)) {
+ LOG.warn("No SSPs are mapped to taskName: {}", taskName.getTaskName());
+ continue;
+ }
+ for (SystemStreamPartition ssp : ssps) {
+ Startpoint startpoint = readStartpoint(ssp); // Read SSP-only key
+ if (startpoint != null) {
+ deleteKeys.put(ssp, null);
+ }
+
+ Startpoint startpointForTask = readStartpoint(ssp, taskName); // Read
SSP+taskName key
+ if (startpointForTask != null) {
+ deleteKeys.put(ssp, taskName);
+ }
+
+ Startpoint startpointWithPrecedence =
resolveStartpointPrecendence(startpoint, startpointForTask);
+ if (startpointWithPrecedence == null) {
+ continue;
+ }
+
+ fanOuts.putIfAbsent(taskName, new StartpointFanOut(now, new
HashMap<>()));
+ fanOuts.get(taskName).getFanOuts().put(ssp, startpointWithPrecedence);
+ }
+ }
+
+ if (fanOuts.isEmpty()) {
+ LOG.debug("No fan outs created.");
+ return ImmutableSet.of();
+ }
+
+ LOG.info("Fanning out to {} tasks", fanOuts.size());
+
+ StartpointFanOut.StartpointFanOutSerde startpointFanOutSerde = new
StartpointFanOut.StartpointFanOutSerde();
+ for (TaskName taskName : fanOuts.keySet()) {
+ String fanOutKey = toFanOutStoreKey(taskName);
+ StartpointFanOut newFanOut = fanOuts.get(taskName);
+ byte[] fanOutFromStoreInBytes = fanOutStore.get(fanOutKey);
+
+ if (ArrayUtils.isNotEmpty(fanOutFromStoreInBytes)) {
+ // Merge new fan out with existing fan out. This is not a typical
scenario but it can happen when the job
+ // restarts before all startpoints are committed by the first
checkpoint commit and new startpoints were written
+ // to the readWriteStore after the previous fan out.
+ StartpointFanOut existingFanOut =
startpointFanOutSerde.fromBytes(fanOutFromStoreInBytes);
+ existingFanOut.getFanOuts().putAll(newFanOut.getFanOuts());
+ newFanOut = existingFanOut;
+ }
+
+ fanOutStore.put(fanOutKey, startpointFanOutSerde.toBytes(newFanOut));
+ // Delete from readWriteStore after fan out.
+ for (SystemStreamPartition ssp : newFanOut.getFanOuts().keySet()) {
+ if (deleteKeys.remove(ssp, taskName)) {
+ deleteStartpoint(ssp, taskName);
+ }
+ if (deleteKeys.remove(ssp, null)) {
+ deleteStartpoint(ssp);
}
}
}
- // Delete SSP-only keys
- sspsToDelete.forEach(ssp -> {
- deleteStartpoint(ssp);
- LOG.info("All Startpoints for SSP: {} have been grouped to the
appropriate tasks and the SSP was deleted.");
- });
+ return ImmutableSet.copyOf(fanOuts.keySet());
+ }
+
+ /**
+ * Read the fanned out {@link Startpoint}s for the given {@link TaskName}
+ * @param taskName to read the fan out Startpoints for
+ * @return fanned out Startpoints
+ */
+ public Map<SystemStreamPartition, Startpoint> getFanOutForTask(TaskName
taskName) {
+ Preconditions.checkState(!stopped, "Underlying metadata store not
available");
+ Preconditions.checkNotNull(taskName, "TaskName cannot be null");
- return ImmutableSet.copyOf(sspsToDelete);
+ StartpointFanOut.StartpointFanOutSerde startpointFanOutSerde = new
StartpointFanOut.StartpointFanOutSerde();
+ byte[] fanOutBytes = fanOutStore.get(toFanOutStoreKey(taskName));
+ if (ArrayUtils.isEmpty(fanOutBytes)) {
+ return null;
+ }
+ StartpointFanOut startpointFanOut =
startpointFanOutSerde.fromBytes(fanOutBytes);
+ return ImmutableMap.copyOf(startpointFanOut.getFanOuts());
}
/**
- * Relinquish resources held by the underlying {@link MetadataStore}
+ * Deletes the fanned out {@link Startpoint} for the given {@link TaskName}
+ * @param taskName to delete the fan out Startpoints for
*/
- public void stop() {
- stopped = true;
- // Metadata store lifecycle is managed outside of the StartpointManager,
so not closing it.
+ public void removeFanOutForTask(TaskName taskName) {
+ Preconditions.checkState(!stopped, "Underlying metadata store not
available");
+ Preconditions.checkNotNull(taskName, "TaskName cannot be null");
+
+ fanOutStore.delete(toFanOutStoreKey(taskName));
}
@VisibleForTesting
MetadataStore getMetadataStore() {
return metadataStore;
}
- private static String toStoreKey(SystemStreamPartition ssp, TaskName
taskName) {
+ @VisibleForTesting
+ MetadataStore getReadWriteStore() {
+ return readWriteStore;
+ }
+
+ @VisibleForTesting
+ MetadataStore getFanOutStore() {
+ return fanOutStore;
+ }
+
+ private static Startpoint resolveStartpointPrecendence(Startpoint
startpoint1, Startpoint startpoint2) {
+ if (startpoint1 != null && startpoint2 != null) {
+ // if SSP-only and SSP+taskName startpoints both exist, resolve to the
one with the latest timestamp
+ if (startpoint1.getCreationTimestamp() >
startpoint2.getCreationTimestamp()) {
+ return startpoint1;
+ }
+ return startpoint2;
+ }
+ return startpoint1 != null ? startpoint1 : startpoint2;
+ }
+
+ private static String toReadWriteStoreKey(SystemStreamPartition ssp,
TaskName taskName) {
return new String(new JsonSerdeV2<>().toBytes(new StartpointKey(ssp,
taskName)));
Review comment:
Is `JsonSerdeV2` guaranteed to keep the same ordering of keys across
different JVMs?
For example, {"ssp": "ssp_value", "taskName": "taskName_value"} is the same
semantic key as {"taskName": "taskName_value", "ssp": "ssp_value"}, but the
byte representation is different.
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