[HUDI-3474] Add more document to Pipelines for the usage of this tool to build a write pipeline (#4906)

hudi-flink/src/main/java/org/apache/hudi/sink/utils/Pipelines.java

@@ -58,6 +58,31 @@ import org.apache.flink.table.types.logical.RowType;
  */
 public class Pipelines {
 
+  /**
+   * Bulk insert the input dataset at once.
+   *
+   * <p>By default, the input dataset would shuffle by the partition path first then
+   * sort by the partition path before passing around to the write function.
+   * The whole pipeline looks like the following:
+   *
+   * <pre>
+   *      | input1 | ===\     /=== |sorter| === | task1 | (p1, p2)
+   *                   shuffle
+   *      | input2 | ===/     \=== |sorter| === | task2 | (p3, p4)
+   *
+   *      Note: Both input1 and input2's dataset come from partitions: p1, p2, p3, p4
+   * </pre>
+   *
+   * <p>The write task switches to new file handle each time it receives a record
+   * from the different partition path, the shuffle and sort would reduce small files.
+   *
+   * <p>The bulk insert should be run in batch execution mode.
+   *
+   * @param conf       The configuration
+   * @param rowType    The input row type
+   * @param dataStream The input data stream
+   * @return the bulk insert data stream sink
+   */
   public static DataStreamSink<Object> bulkInsert(Configuration conf, RowType rowType, DataStream<RowData> dataStream) {
     WriteOperatorFactory<RowData> operatorFactory = BulkInsertWriteOperator.getFactory(conf, rowType);
 
@@ -95,6 +120,27 @@ public class Pipelines {
         .name("dummy");
   }
 
+  /**
+   * Insert the dataset with append mode(no upsert or deduplication).
+   *
+   * <p>The input dataset would be rebalanced among the write tasks:
+   *
+   * <pre>
+   *      | input1 | ===\     /=== | task1 | (p1, p2, p3, p4)
+   *                   shuffle
+   *      | input2 | ===/     \=== | task2 | (p1, p2, p3, p4)
+   *
+   *      Note: Both input1 and input2's dataset come from partitions: p1, p2, p3, p4
+   * </pre>
+   *
+   * <p>The write task switches to new file handle each time it receives a record
+   * from the different partition path, so there may be many small files.
+   *
+   * @param conf       The configuration
+   * @param rowType    The input row type
+   * @param dataStream The input data stream
+   * @return the appending data stream sink
+   */
   public static DataStreamSink<Object> append(Configuration conf, RowType rowType, DataStream<RowData> dataStream) {
     WriteOperatorFactory<RowData> operatorFactory = AppendWriteOperator.getFactory(conf, rowType);
 
@@ -108,6 +154,8 @@ public class Pipelines {
 
   /**
    * Constructs bootstrap pipeline as streaming.
+   * The bootstrap operator loads the existing data index (primary key to file id mapping),
+   * then sends the indexing data set to subsequent operator(usually the bucket assign operator).
    */
   public static DataStream<HoodieRecord> bootstrap(
       Configuration conf,
@@ -119,6 +167,8 @@ public class Pipelines {
 
   /**
    * Constructs bootstrap pipeline.
+   * The bootstrap operator loads the existing data index (primary key to file id mapping),
+   * then send the indexing data set to subsequent operator(usually the bucket assign operator).
    *
    * @param conf The configuration
    * @param rowType The row type
@@ -165,6 +215,11 @@ public class Pipelines {
     return dataStream1;
   }
 
+  /**
+   * Constructs bootstrap pipeline for batch execution mode.
+   * The indexing data set is loaded before the actual data write
+   * in order to support batch UPSERT.
+   */
   private static DataStream<HoodieRecord> boundedBootstrap(
       Configuration conf,
       RowType rowType,
@@ -184,10 +239,36 @@ public class Pipelines {
         .uid("uid_batch_index_bootstrap_" + conf.getString(FlinkOptions.TABLE_NAME));
   }
 
+  /**
+   * Transforms the row data to hoodie records.
+   */
   public static DataStream<HoodieRecord> rowDataToHoodieRecord(Configuration conf, RowType rowType, DataStream<RowData> dataStream) {
     return dataStream.map(RowDataToHoodieFunctions.create(rowType, conf), TypeInformation.of(HoodieRecord.class));
   }
 
+  /**
+   * The streaming write pipeline.
+   *
+   * <p>The input dataset shuffles by the primary key first then
+   * shuffles by the file group ID before passing around to the write function.
+   * The whole pipeline looks like the following:
+   *
+   * <pre>
+   *      | input1 | ===\     /=== | bucket assigner | ===\     /=== | task1 |
+   *                   shuffle(by PK)                    shuffle(by bucket ID)
+   *      | input2 | ===/     \=== | bucket assigner | ===/     \=== | task2 |
+   *
+   *      Note: a file group must be handled by one write task to avoid write conflict.
+   * </pre>
+   *
+   * <p>The bucket assigner assigns the inputs to suitable file groups, the write task caches
+   * and flushes the data set to disk.
+   *
+   * @param conf       The configuration
+   * @param defaultParallelism The default parallelism
+   * @param dataStream The input data stream
+   * @return the stream write data stream pipeline
+   */
   public static DataStream<Object> hoodieStreamWrite(Configuration conf, int defaultParallelism, DataStream<HoodieRecord> dataStream) {
     WriteOperatorFactory<HoodieRecord> operatorFactory = StreamWriteOperator.getFactory(conf);
     return dataStream
@@ -206,6 +287,26 @@ public class Pipelines {
         .setParallelism(conf.getInteger(FlinkOptions.WRITE_TASKS));
   }
 
+  /**
+   * The compaction tasks pipeline.
+   *
+   * <p>The compaction plan operator monitors the new compaction plan on the timeline
+   * then distributes the sub-plans to the compaction tasks. The compaction task then
+   * handle over the metadata to commit task for compaction transaction commit.
+   * The whole pipeline looks like the following:
+   *
+   * <pre>
+   *                                           /=== | task1 | ===\
+   *      | plan generation | ===> re-balance                      | commit |
+   *                                           \=== | task2 | ===/
+   *
+   *      Note: both the compaction plan generation task and commission task are singleton.
+   * </pre>
+   *
+   * @param conf       The configuration
+   * @param dataStream The input data stream
+   * @return the compaction pipeline
+   */
   public static DataStreamSink<CompactionCommitEvent> compact(Configuration conf, DataStream<Object> dataStream) {
     return dataStream.transform("compact_plan_generate",
         TypeInformation.of(CompactionPlanEvent.class),