Requirements
Generic Token support (not only MR counters)
- Ability for the user to access the token set by any node in the Workflow
- Persist token per Workflow run in the MDS
- View token set by specific node in the Workflow
Assumptions
Generic information in the token is of the key-value type, each represented by String.
Potential Changes
WorkflowToken interface changes
/** * Interface to represent the data that is transferred from one node to the next node in the {@link Workflow}. */ public interface WorkflowToken { /** * Put the specified key-value entry in the {@link WorkflowToken}. * The token may store additional information about the context in which * this key is being set, for example, the unique name of the workflow node. * @param key the key representing the entry * @param value the value for the key */ void setValue(String key, String value); /** * Same key can be added to the WorkflowToken by multiple nodes. * This method returns the {@link List} of unique node names to the values * that were added by the nodes for the specified key. The list maintains * the order in which the values were inserted in the WorkflowToken for a * specific key. In case of fork in the Workflow, copies of the WorkflowToken * are made and passed it along the each branch. At the join, all copies of the * WorkflowToken are merged together. While merging, the values from the branch * that was completed first will be added first to the WorkflowToken. * * Example: Consider that the following values were added to the Workflow * for the key "myKey". Numbers associated with the values represent * unique node names - * * 3 4 * |-->D-->E--| * A-->B-->C--> >-->H-->I * 0 1 2 |-->F-->G--| 7 8 * 5 6 * * Assume that the branch containing node 5 finishes the execution first. * * Now the method invocation getValues("myKey") will return the list * in which the keys will be ordered as 0-1-2-5-6-3-4-7-8. * * @param key the key to be searched * @return the list of entries from node name to the value that node * added for the input key */ List<NodeValueEntry> getValues(String key); /** * Get the value set for the specified key by specified node. * @param key the key to be searched * @param nodeName the name of the node * @return the value set for the key by nodeName */ @Nullable String getValue(String key, String nodeName); /** * Get the most recent value for the specified key. * @param key the key to be searched * @return the value for the key */ @Nullable String getValue(String key); /** * This method is deprecated as of release 3.1. Instead to get the * MapReduce counters from the WorkflowToken, use the flatten key prefixed * by 'mr.counters.'. * * Example: * 1. To get the most recent value of counter with group name * 'org.apache.hadoop.mapreduce.TaskCounter' and counter name 'MAP_INPUT_RECORDS' * * String flattenCounterKey = "mr.counters.org.apache.hadoop.mapreduce.TaskCounter.MAP_INPUT_RECORDS"; * workflowToken.getValue(flattenCounterKey); * * 2. To get the value of counter with group name 'org.apache.hadoop.mapreduce.TaskCounter' * and counter name 'MAP_INPUT_RECORDS' as set by MapReduce program with unique name 'PurchaseHistoryBuilder' * * String flattenCounterKey = "mr.counters.org.apache.hadoop.mapreduce.TaskCounter.MAP_INPUT_RECORDS"; * workflowToken.getValue(flattenCounterKey, "PurchaseHistoryBuilder"); * * Get the Hadoop counters from the previous MapReduce program in the Workflow. * The method returns null if the counters are not set. * @return the Hadoop MapReduce counters set by the previous MapReduce program */ @Deprecated @Nullable Map<String, Map<String, Long>> getMapReduceCounters(); /** * Return true if the {@link WorkflowToken} contains the specified key. * @param key the key to be tested for the presence in the {@link WorkflowToken} * @return the result of the test */ boolean containsKey(String key); }
The method getValues(String key) in the above interface returns the List of NodeValueEntry objects. NodeValueEntry class represents nodeName and value that the node put for the specific key./** * Multiple nodes in the Workflow can add the same key to the {@link WorkflowToken}. * This class provides a mapping from node name to the value which was set for the * specific key. */ public final class NodeValueEntry { private final String nodeName; private final String value; public NodeValueEntry(String nodeName, String value) { this.nodeName = nodeName; this.value = value; } public String getNodeName() { return nodeName; } public String getValue() { return value; } ... // other methods like toString(), equals() and hashCode() ... }WorkflowConfigurer interface changes
We generate unique numeric node ids for each node when the application is deployed. However, while writing the Workflow, users will not be aware of the node id associated with each node in the Workflow. Since WorkflowToken stores the MapReduce counters and other information per node level, users should be able to get the value of a particular key from the token as set by the particular program in the Workflow.
If the program is used only once in a Workflow, then the user can use its name to query for the token information. However, we allow the same program to occur multiple times in a Workflow. In that case, the program name will not be sufficient to access the token.
The WorkflowConfigurer API can be updated to allow a user to set a unique name for the program, if it occurs multiple times in a Workflow and use that unique name to retrieve the token.
/** * Add MapReduce program to the {@link Workflow}. * @param uniqueName the unique name for the MapReduce program which will be used * to identify particular occurrence of the program in the Workflow * @param mapReduceName the name of the MapReduce program */ void addMapReduce(String uniqueName, String mapReduceName);
WorkflowToken can also be updated from a predicate on the condition node. In the presence of multiple condition nodes in a Workflow, we will need the ability to specify unique names for the conditions as well so that token values from specific condition nodes can be fetched./** * Adds a condition with the unique name to the {@link Workflow}. * @param conditionName the unique name to be assigned to the condition * @param condition the {@link Predicate} to be evaluated for the condition * @return the configurer for the condition */ WorkflowConditionConfigurer<? extends WorkflowConfigurer> condition(String conditionName, Predicate<WorkflowContext> condition);Provide ability to set and get information in the WorkflowToken
1. MapReduce program: Users should be able to access and modify WorkflowToken from "beforeSubmit" and "onFinish" methods of the MapReduce program. Since these methods get the MapReduceContext, we will need to update the MapReduceContext interface to get the WorkflowToken./** * If {@link MapReduce} program is executed as a part of the {@link Workflow} * then get the {@link WorkflowToken} associated with the current run, otherwise return null. * @return the {@link WorkflowToken} if available */ @Nullable WorkflowToken getWorkflowToken();Consider the following code sample to update the WorkflowToken in the MapReduce program:
@Override public void beforeSubmit(MapReduceContext context) throws Exception { ... WorkflowToken workflowToken = context.getWorkflowToken(); if (workflowToken != null) { // Put the action type in the WorkflowToken workflowToken.setValue("action", "MAPREDUCE"); // Put the start time for the action workflowToken.setValue("startTime", String.valueOf(System.currentTimeMillis())); } ... } @Override public void onFinish(boolean succeeded, MapReduceContext context) throws Exception { ... WorkflowToken workflowToken = context.getWorkflowToken(); if (workflowToken != null) { // Put the end time for the action workflowToken.setValue("endTime", String.valueOf(System.currentTimeMillis())); } ... }2. Spark program: Users should be able to access and modify WorkflowToken from "beforeSubmit" and "onFinish" methods of the Spark program. Since these methods get the SparkContext, we will need to update the SparkContext interface to get the WorkflowToken.
/** * If {@link Spark} program is executed as a part of the {@link Workflow} * then get the {@link WorkflowToken} associated with the current run, otherwise return null. * @return the {@link WorkflowToken} if available */ @Nullable WorkflowToken getWorkflowToken();3. Custom Workflow action: Since custom workflow actions already receive WorkflowContext, no changes are anticipated in the interface.
Following is the sample code to get values from the WorkflowToken in custom action:
@Override public void run() { ... WorkflowToken token = getContext().getToken(); // set the type of the action of the current node token.setValue("action", "CUSTOM_ACTION"); // Assuming that every node in the Workflow adds the key "action" with the value as action type in the WorkflowToken List<NodeValueEntry> nodeValues = token.getValues("action"); // To get the number of nodes executed by the Workflow - nodeValues.size(); // Simply iterate over the nodeValues to get the order in which the nodes were executed. // To get the start time of the MapReduce program with unique name "PurchaseHistoryBuilder" String startTime = token.getValue("startTime", "PurchaseHistoryBuilder"); // To get the most recent value of counter with group name // 'org.apache.hadoop.mapreduce.TaskCounter' and counter name 'MAP_INPUT_RECORDS' String flattenCounterKey = "mr.counters.org.apache.hadoop.mapreduce.TaskCounter.MAP_INPUT_RECORDS"; workflowToken.getValue(flattenCounterKey); // To get the value of counter with group name 'org.apache.hadoop.mapreduce.TaskCounter' // and counter name 'MAP_INPUT_RECORDS' as set by MapReduce program with unique name 'PurchaseHistoryBuilder' workflowToken.getValue(flattenCounterKey, "PurchaseHistoryBuilder"); ... }- WorkflowToken in presence of Fork and Join
When a fork is encountered in the Workflow, we make a copy of the WorkflowToken and pass it along to each branch. At the join, we create a new WorkflowToken, which will be a merge of the WorkflowTokens associated with each of the branches of the fork. Since we are storing the information in the token at the node level, there will not be any conflicts during the merge process. - Persisting the WorkflowToken
The RunRecord for the Workflow will contain the WorkflowToken as its property. This token will be updated before the execution of the action in the Workflow. We will add a version field to the RunRecord itself which will help in the upgrade process. - RESTful end-points to access the value of the WorkflowToken that was received by an individual node in the WorkflowWe will expose a RESTful end point to retrieve the token values that were set by a particular node as identified by its unique name.
/apps/{app-id}/workflows/{workflow-name}/runs/{run-id}/nodes/{unique-node-name}/token