luocooong commented on a change in pull request #2419:
URL: https://github.com/apache/drill/pull/2419#discussion_r795557310
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File path:
exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/scan/ScanOperatorExec.java
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@@ -32,6 +32,24 @@
* Implementation of the revised scan operator that uses a mutator aware of
* batch sizes. This is the successor to {@link ScanBatch} and should be used
* by all new scan implementations.
+ * <p>
+ * The basic concept is to split the scan operator into layers:
+ * <ul>
+ * <li>The {@code OperatorRecordBatch} which implements Drill's Volcano-like
+ * protocol.</li>
+ * <li>The scan operator "wrapper" (this class) which implements actions for
the
+ * operator record batch specifically for scan. It iterates over readers,
+ * delegating semantic work to other classes.</li>
+ * <li>The implementation of per-reader semantics in the two EVF versions and
+ * other ad-hoc implementations.</li>
+ * <li>The result set loader and related classes which pack values into
+ * value vectors.</li>
+ * <li>Value vectors, which store the data.</li>
+ * </ul>
+ * <p>
+ * The layered format can be confusing. However, each layer is somewhat
+ * complex, so dividing the work into layers keeps the overall complexity
+ * somewhat under control.
Review comment:
Thank you.
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