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https://issues.apache.org/jira/browse/DRILL-5546?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16135706#comment-16135706
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ASF GitHub Bot commented on DRILL-5546:
---------------------------------------
Github user paul-rogers commented on a diff in the pull request:
https://github.com/apache/drill/pull/906#discussion_r134299504
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/ScanBatch.java
---
@@ -329,9 +326,11 @@ public TypedFieldId getValueVectorId(SchemaPath path) {
@VisibleForTesting
public static class Mutator implements OutputMutator {
- /** Whether schema has changed since last inquiry (via #isNewSchema}).
Is
- * true before first inquiry. */
- private boolean schemaChanged = true;
+ /** Flag keeping track whether top-level schema has changed since last
inquiry (via #isNewSchema}).
+ * It's initialized to false, or reset to false after #isNewSchema or
after #clear, until a new value vector
+ * or a value vector with different type is added to fieldVectorMap.
+ **/
+ private boolean schemaChanged;
--- End diff --
Using a flag is very messy. The new version uses a counter. An observer
simply remembers the previous count and compares it against the current count.
Allows multiple observers without negotiating over which is responsible for
resetting the flag.
> Schema change problems caused by empty batch
> --------------------------------------------
>
> Key: DRILL-5546
> URL: https://issues.apache.org/jira/browse/DRILL-5546
> Project: Apache Drill
> Issue Type: Bug
> Reporter: Jinfeng Ni
> Assignee: Jinfeng Ni
>
> There have been a few JIRAs opened related to schema change failure caused by
> empty batch. This JIRA is opened as an umbrella for all those related JIRAS (
> such as DRILL-4686, DRILL-4734, DRILL4476, DRILL-4255, etc).
>
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