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https://issues.apache.org/jira/browse/KYLIN-3617?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16714233#comment-16714233
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ASF GitHub Bot commented on KYLIN-3617:
---------------------------------------
shaofengshi closed pull request #376: KYLIN-3617 Add javadoc for magic number
in isTaskExecutableOutput
URL: https://github.com/apache/kylin/pull/376
This is a PR merged from a forked repository.
As GitHub hides the original diff on merge, it is displayed below for
the sake of provenance:
As this is a foreign pull request (from a fork), the diff is supplied
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diff --git a/core-job/src/main/java/org/apache/kylin/job/dao/ExecutableDao.java
b/core-job/src/main/java/org/apache/kylin/job/dao/ExecutableDao.java
index 4e7188a71c..a4dc4c1d87 100644
--- a/core-job/src/main/java/org/apache/kylin/job/dao/ExecutableDao.java
+++ b/core-job/src/main/java/org/apache/kylin/job/dao/ExecutableDao.java
@@ -31,6 +31,8 @@
import org.apache.kylin.common.persistence.Serializer;
import org.apache.kylin.common.util.AutoReadWriteLock;
import org.apache.kylin.job.exception.PersistentException;
+import org.apache.kylin.job.execution.AbstractExecutable;
+import org.apache.kylin.job.execution.DefaultChainedExecutable;
import org.apache.kylin.metadata.cachesync.Broadcaster;
import org.apache.kylin.metadata.cachesync.CachedCrudAssist;
import org.apache.kylin.metadata.cachesync.CaseInsensitiveStringCache;
@@ -164,8 +166,29 @@ protected ExecutableOutputPO
initEntityAfterReload(ExecutableOutputPO entity, St
Broadcaster.getInstance(config).registerListener(new
JobOutputSyncListener(), "execute_output");
}
+ /**
+ * Length of java.util.UUID's string representation is always 36.
+ */
+ private static final int UUID_STRING_REPRESENTATION_LENGTH = 36;
+
+ /**
+ * <pre>
+ * Backgroud :
+ * 1. Each Executable has id, and id should be unique, we use
java.util.UUID to create id of Executable.
+ * 2. 36(UUID_STRING_REPRESENTATION_LENGTH) is a magic number, and it is
the length of string of java.util.UUID.toString(). It can verified this simply
by `System.out.println(UUID.randomUUID().toString().length());`
+ * 3. All subtask of a ChainedExecutable is also a Executable, its id is a
string which length is 39 (36 + 3). See DefaultChainedExecutable#addTask.
+ * 4. Any other Executable's id is a String created by UUID.toString(), so
its length is 36.
+ * 5. This method may be a bit fragile/confusing because it depend on
specific implementation of subclass of Executable.
+ * </pre>
+ *
+ * @see DefaultChainedExecutable#addTask(AbstractExecutable)
+ * @see AbstractExecutable#AbstractExecutable()
+ *
+ * @param id id of a Executable (mostly it is a UUID)
+ * @return true if the job is a subtask of a ChainedExecutable; else
return false
+ */
private boolean isTaskExecutableOutput(String id) {
- return id.length() > 36;
+ return id.length() > UUID_STRING_REPRESENTATION_LENGTH;
}
private class JobSyncListener extends Broadcaster.Listener {
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> Reduce number of visiting metastore for job scheduler
> -----------------------------------------------------
>
> Key: KYLIN-3617
> URL: https://issues.apache.org/jira/browse/KYLIN-3617
> Project: Kylin
> Issue Type: Improvement
> Components: Job Engine
> Affects Versions: v2.4.1
> Reporter: nichunen
> Assignee: nichunen
> Priority: Major
> Fix For: v2.6.0
>
> Attachments: image-2018-12-09-20-22-51-336.png,
> image-2018-12-09-20-24-30-590.png, image-2018-12-09-20-25-40-265.png,
> image-2018-12-09-20-26-30-105.png, image-2018-12-09-20-26-40-478.png
>
>
> For KYLIN-3470 introduced cache for jobs' metadata, it's also can be used in
> job scheduler to reduce the pressure on metastore
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