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https://issues.apache.org/jira/browse/SPARK-2721?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael Armbrust resolved SPARK-2721.
-------------------------------------
Resolution: Fixed
Fix Version/s: 1.1.0
> Fix MapType compatibility issues with reading Parquet datasets
> --------------------------------------------------------------
>
> Key: SPARK-2721
> URL: https://issues.apache.org/jira/browse/SPARK-2721
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 1.0.1
> Reporter: Robbie Russo
> Fix For: 1.1.0
>
>
> Parquet-thrift (along with most likely other implementations of parquet)
> supports null values in a map and this makes any thrift generated parquet
> files that contain a map unreadable by spark sql due to the following code in
> parquet-thrift for generating the schema for maps:
> {code:title=parquet.thrift.ThriftSchemaConverter.java|borderStyle=solid}
> @Override
> public void visit(ThriftType.MapType mapType) {
> final ThriftField mapKeyField = mapType.getKey();
> final ThriftField mapValueField = mapType.getValue();
> //save env for map
> String mapName = currentName;
> Type.Repetition mapRepetition = currentRepetition;
> //=========handle key
> currentFieldPath.push(mapKeyField);
> currentName = "key";
> currentRepetition = REQUIRED;
> mapKeyField.getType().accept(this);
> Type keyType = currentType;//currentType is the already converted type
> currentFieldPath.pop();
> //=========handle value
> currentFieldPath.push(mapValueField);
> currentName = "value";
> currentRepetition = OPTIONAL;
> mapValueField.getType().accept(this);
> Type valueType = currentType;
> currentFieldPath.pop();
> if (keyType == null && valueType == null) {
> currentType = null;
> return;
> }
> if (keyType == null && valueType != null)
> throw new ThriftProjectionException("key of map is not specified in
> projection: " + currentFieldPath);
> //restore Env
> currentName = mapName;
> currentRepetition = mapRepetition;
> currentType = ConversionPatterns.mapType(currentRepetition, currentName,
> keyType,
> valueType);
> }
> {code}
> Which causes an error on the spark side when we reach this step in the
> toDataType function that asserts that both the key and value are of
> repetition level REQUIRED:
> {code:title=org.apache.spark.sql.parquet.ParquetTypes.scala|borderStyle=solid}
> case ParquetOriginalType.MAP => {
> assert(
> !groupType.getFields.apply(0).isPrimitive,
> "Parquet Map type malformatted: expected nested group for map!")
> val keyValueGroup = groupType.getFields.apply(0).asGroupType()
> assert(
> keyValueGroup.getFieldCount == 2,
> "Parquet Map type malformatted: nested group should have 2 (key,
> value) fields!")
> val keyType = toDataType(keyValueGroup.getFields.apply(0))
> println("here")
> assert(keyValueGroup.getFields.apply(0).getRepetition ==
> Repetition.REQUIRED)
> val valueType = toDataType(keyValueGroup.getFields.apply(1))
> assert(keyValueGroup.getFields.apply(1).getRepetition ==
> Repetition.REQUIRED)
> new MapType(keyType, valueType)
> }
> {code}
> Currently I have modified parquet-thrift to use repetition REQUIRED just to
> make spark sql able to work on the parquet files since we don't actually use
> null values in our maps. However it would be preferred to use parquet-thrift
> and spark sql out of the box and have them work nicely together with our
> existing thrift data types without having to modify dependencies.
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