agavra commented on code in PR #9711:
URL: https://github.com/apache/pinot/pull/9711#discussion_r1014154668
##########
pinot-common/src/main/java/org/apache/pinot/common/datablock/MetadataBlock.java:
##########
@@ -18,28 +18,118 @@
*/
package org.apache.pinot.common.datablock;
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.google.common.annotations.VisibleForTesting;
import java.io.IOException;
import java.nio.ByteBuffer;
-import org.apache.pinot.common.utils.DataSchema;
/**
- * Wrapper for row-wise data table. It stores data in row-major format.
+ * A block type to indicate some metadata about the current processing state.
+ * For the different types of metadata blocks see {@link MetadataBlockType}.
*/
public class MetadataBlock extends BaseDataBlock {
- private static final int VERSION = 1;
- public MetadataBlock() {
- super(0, null, new String[0], new byte[]{0}, new byte[]{0});
+ private static final ObjectMapper JSON = new ObjectMapper();
+
+ @VisibleForTesting
+ static final int VERSION = 1;
+
+ public enum MetadataBlockType {
+ /**
+ * Indicates that this block is the final block to be sent
+ * (End Of Stream) as part of an operator chain computation.
+ */
+ EOS,
+
+ /**
+ * An {@code ERROR} metadata block indicates that there was
+ * some error during computation. To retrieve the error that
+ * occurred, use {@link MetadataBlock#getExceptions()}
+ */
+ ERROR,
+
+ /**
+ * A {@code NOOP} metadata block can be sent at any point to
+ * and should be ignored by downstream - it is often used to
+ * indicate that the operator chain either has nothing to process
+ * or has processed data but is not yet ready to emit a result
+ * block.
+ */
+ NOOP;
+
+ MetadataBlockType() {
+ }
}
- public MetadataBlock(DataSchema dataSchema) {
- super(0, dataSchema, new String[0], new byte[]{0}, new byte[]{0});
+ /**
+ * Used to serialize the contents of the metadata block conveniently and in
+ * a backwards compatible way. Use JSON because the performance of metadata
block
+ * SerDe should not be a bottleneck.
+ */
+ @JsonIgnoreProperties(ignoreUnknown = true)
+ @VisibleForTesting
+ static class Contents {
+
+ private String _type;
+
+ @JsonCreator
+ public Contents(@JsonProperty("type") String type) {
+ _type = type;
+ }
+
+ @JsonCreator
+ public Contents() {
+ _type = null;
+ }
+
+ public String getType() {
+ return _type;
+ }
+
+ public void setType(String type) {
+ _type = type;
+ }
+ }
+
+ private final Contents _contents;
+
+ public MetadataBlock(MetadataBlockType type) {
+ super(0, null, new String[0], new byte[]{0}, toContents(new
Contents(type.name())));
+ _contents = new Contents(type.name());
+ }
+
+ private static byte[] toContents(Contents type) {
+ try {
+ return JSON.writeValueAsBytes(type);
+ } catch (JsonProcessingException e) {
+ throw new RuntimeException(e);
+ }
}
public MetadataBlock(ByteBuffer byteBuffer)
throws IOException {
super(byteBuffer);
+ if (_variableSizeDataBytes != null) {
+ _contents = JSON.readValue(_variableSizeDataBytes, Contents.class);
+ } else {
+ _contents = new Contents();
+ }
+ }
+
+ public MetadataBlockType getType() {
+ String type = _contents.getType();
+
+ // if type is null, then we're reading a legacy block where we didn't
encode any
+ // data. assume that it is an EOS block if there's no exceptions and an
ERROR block
+ // otherwise
+ return type == null
+ ? (getExceptions().isEmpty() ? MetadataBlockType.EOS :
MetadataBlockType.ERROR)
+ : MetadataBlockType.valueOf(type);
Review Comment:
I was very careful to make sure that it won't throw when deserializing (see
the tests). is there any reason why we don't need to consider backwards
compatibility? if I don't then I can be less hacky in the serialization format!
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