jcmcote commented on a change in pull request #1500: DRILL-6820: Msgpack format
reader
URL: https://github.com/apache/drill/pull/1500#discussion_r231340882
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File path:
contrib/format-msgpack/src/main/java/org/apache/drill/exec/store/msgpack/MsgpackSchema.java
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@@ -0,0 +1,114 @@
+package org.apache.drill.exec.store.msgpack;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+
+import org.apache.commons.io.IOUtils;
+import org.apache.drill.common.exceptions.DrillRuntimeException;
+import org.apache.drill.common.types.TypeProtos.MinorType;
+import org.apache.drill.exec.exception.SchemaChangeRuntimeException;
+import org.apache.drill.exec.proto.UserBitShared.SerializedField;
+import org.apache.drill.exec.proto.UserBitShared.SerializedField.Builder;
+import org.apache.drill.exec.record.MaterializedField;
+import org.apache.drill.exec.store.dfs.DrillFileSystem;
+import org.apache.drill.shaded.guava.com.google.common.base.Preconditions;
+import org.apache.hadoop.fs.FSDataInputStream;
+import org.apache.hadoop.fs.FSDataOutputStream;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.security.AccessControlException;
+
+import com.google.protobuf.TextFormat;
+import com.google.protobuf.TextFormat.ParseException;
+
+public class MsgpackSchema {
+ public static final String SCHEMA_FILE_NAME = ".schema.proto";
+
+ @SuppressWarnings("unused")
+ private static final org.slf4j.Logger logger =
org.slf4j.LoggerFactory.getLogger(MsgpackSchema.class);
+
+ private DrillFileSystem fileSystem;
+
+ public MsgpackSchema(DrillFileSystem fileSystem) {
+ this.fileSystem = fileSystem;
+ }
+
+ public MaterializedField load(Path schemaLocation) throws
AccessControlException, FileNotFoundException, IOException {
+ MaterializedField previousMapField = null;
+ if (schemaLocation != null && fileSystem.exists(schemaLocation)) {
+ try (FSDataInputStream in = fileSystem.open(schemaLocation)) {
+ String schemaData = IOUtils.toString(in);
+ Builder newBuilder = SerializedField.newBuilder();
+ try {
+ TextFormat.merge(schemaData, newBuilder);
+ } catch (ParseException e) {
+ throw new DrillRuntimeException("Failed to read schema file: " +
schemaLocation, e);
+ }
+ SerializedField read = newBuilder.build();
+ previousMapField = MaterializedField.create(read);
+ }
+ }
+ return previousMapField;
+ }
+
+ public void save(MaterializedField mapField, Path schemaLocation) throws
IOException {
+ try (FSDataOutputStream out = fileSystem.create(schemaLocation, true)) {
+ SerializedField serializedMapField = mapField.getSerializedField();
+ String data = TextFormat.printToString(serializedMapField);
+ IOUtils.write(data, out);
+ }
+ }
+
+ public MaterializedField merge(MaterializedField existingField,
MaterializedField newField) {
Review comment:
I don't handle multi-files in parallel right now.
Schema evolution is also not handled. You will recall from my questions in
the dev mailing list, I have come across cases where an array would have
VARCHAR and VARBINARY. In that case I would get a schema with array of type
VARCHAR (having skipped over the error of not being able to write VARBINARY
into that array.
By looking at the logs I can see these values are being skipped. I then
manually update the schema to tell it I want that array to be VARBINARY. From
now one when I read the VARCHAR values are coerced into VARBINARY.
So for now I use the schema learning to discover the bulk of the structure
and fix any edge cases manually.
But I think the bases are there to build a smarter discovery mechanism where
it could evolve the schema as it sees more of the data.
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