Add comments to query handlers

Signed-off-by: Tomoyuki Morita <[email protected]>

spark/src/main/java/org/opensearch/sql/spark/dispatcher/BatchQueryHandler.java

@@ -28,6 +28,11 @@
 import org.opensearch.sql.spark.leasemanager.model.LeaseRequest;
 import org.opensearch.sql.spark.response.JobExecutionResponseReader;
 
+/**
+ * The handler for batch query.
+ * With batch query, queries are executed as single batch. The queries are sent along with job
+ * execution request to spark.
+ */
 @RequiredArgsConstructor
 public class BatchQueryHandler extends AsyncQueryHandler {
   private final EMRServerlessClient emrServerlessClient;

spark/src/main/java/org/opensearch/sql/spark/dispatcher/IndexDMLHandler.java

@@ -36,7 +36,12 @@
 import org.opensearch.sql.spark.flint.operation.FlintIndexOpVacuum;
 import org.opensearch.sql.spark.response.JobExecutionResponseReader;
 
-/** Handle Index DML query. includes * DROP * ALT? */
+/**
+ * The handler for Index DML (Data Manipulation Language) query.
+ * Handles DROP/ALT/VACUUM operation for flint indices.
+ * It will stop streaming query job as needed (e.g. when the flint index is automatically updated
+ * by a streaming query, the streaming query is stopped when the index is dropped)
+ */
 @RequiredArgsConstructor
 public class IndexDMLHandler extends AsyncQueryHandler {
   private static final Logger LOG = LogManager.getLogger();

spark/src/main/java/org/opensearch/sql/spark/dispatcher/InteractiveQueryHandler.java

@@ -35,6 +35,12 @@
 import org.opensearch.sql.spark.leasemanager.model.LeaseRequest;
 import org.opensearch.sql.spark.response.JobExecutionResponseReader;
 
+/**
+ * The handler for interactive query.
+ * With interactive query, a session will be first established and then the session will be reused
+ * for the following queries(statements). Session is an abstraction of spark job, and once the job
+ * is started, the job will continuously poll the statements and execute query specified in it.
+ */
 @RequiredArgsConstructor
 public class InteractiveQueryHandler extends AsyncQueryHandler {
   private final SessionManager sessionManager;

spark/src/main/java/org/opensearch/sql/spark/dispatcher/RefreshQueryHandler.java

@@ -21,7 +21,11 @@
 import org.opensearch.sql.spark.leasemanager.LeaseManager;
 import org.opensearch.sql.spark.response.JobExecutionResponseReader;
 
-/** Handle Refresh Query. */
+/**
+ * The handler for refresh query.
+ * Refresh query is one time query request to refresh(update) flint index, and new job is submitted
+ * to Spark.
+ */
 public class RefreshQueryHandler extends BatchQueryHandler {
 
   private final FlintIndexMetadataService flintIndexMetadataService;

spark/src/main/java/org/opensearch/sql/spark/dispatcher/StreamingQueryHandler.java

@@ -26,7 +26,11 @@
 import org.opensearch.sql.spark.leasemanager.model.LeaseRequest;
 import org.opensearch.sql.spark.response.JobExecutionResponseReader;
 
-/** Handle Streaming Query. */
+/**
+ * The handler for streaming query.
+ * Streaming query is a job to continuously update flint index.
+ * Once started, the job can be stopped by IndexDML query.
+ */
 public class StreamingQueryHandler extends BatchQueryHandler {
   private final EMRServerlessClient emrServerlessClient;