[GitHub] [druid] samarthjain commented on a change in pull request #10920: Spark Direct Readers and Writers for Druid.

[GitBox <gi...@apache.org>]

samarthjain commented on a change in pull request #10920:
URL: https://github.com/apache/druid/pull/10920#discussion_r613868557



##########
File path: extensions-core/spark-extensions/src/main/scala/org/apache/druid/spark/clients/DruidClient.scala
##########
@@ -0,0 +1,180 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.spark.clients
+
+import com.fasterxml.jackson.core.`type`.TypeReference
+import com.fasterxml.jackson.databind.ObjectMapper
+import com.google.common.net.HostAndPort
+import org.apache.druid.java.util.common.{ISE, StringUtils}
+import org.apache.druid.java.util.http.client.response.{StringFullResponseHandler,
+  StringFullResponseHolder}
+import org.apache.druid.java.util.http.client.{HttpClient, Request}
+import org.apache.druid.query.Druids
+import org.apache.druid.query.metadata.metadata.{ColumnAnalysis, SegmentAnalysis,
+  SegmentMetadataQuery}
+import org.apache.druid.spark.MAPPER
+import org.apache.druid.spark.configuration.{Configuration, DruidConfigurationKeys}
+import org.apache.druid.spark.mixins.Logging
+import org.jboss.netty.handler.codec.http.{HttpMethod, HttpResponseStatus}
+import org.joda.time.{Duration, Interval}
+
+import java.net.URL
+import java.util.{List => JList}
+import javax.ws.rs.core.MediaType
+import scala.collection.JavaConverters.{asScalaBufferConverter, mapAsJavaMapConverter,
+  mapAsScalaMapConverter, seqAsJavaListConverter}
+
+/**
+  * Going with SegmentMetadataQueries despite the significant overhead because there's no other way
+  * to get accurate information about Druid columns.
+  *
+  * This is pulled pretty directly from the druid-hadoop-input-format project on GitHub. There is
+  * likely substantial room for improvement.
+  *
+  * @param httpClient
+  * @param objectMapper
+  * @param hostAndPort
+  */
+class DruidClient(
+                   val httpClient: HttpClient,
+                   val objectMapper: ObjectMapper,
+                   val hostAndPort: HostAndPort
+                 ) extends Logging {
+  private val RETRY_COUNT = 5
+  private val RETRY_WAIT_SECONDS = 5
+  private val TIMEOUT_MILLISECONDS = 300000
+  private val druidBaseQueryURL: HostAndPort => String =
+    (hostAndPort: HostAndPort) => s"http://$hostAndPort/druid/v2/"
+
+  /**
+    * The SQL system catalog tables are incorrect for multivalue columns and don't have accurate
+    * type info, so we need to fall back to segmentMetadataQueries. Given a DATASOURCE and a range
+    * of INTERVALS to query over, return a map from column name to a tuple of
+    * (columnType, hasMultipleValues). Note that this is a very expensive operation over large
+    * numbers of segments. If possible, this method should only be called with the most granular
+    * starting and ending intervals instead of over a larger interval.
+    *
+    * @param dataSource The Druid dataSource to fetch the schema for.
+    * @param intervals  The intervals to return the schema for.
+    * @return A map from column name to data type and whether or not the column is multi-value
+    *         for the schema of DATASOURCE.
+    */
+  def getSchema(dataSource: String, intervals: List[Interval]): Map[String, (String, Boolean)] = {

Review comment:
       Should intervals be optional? If interval is not provided, the default interval specified by the broker config `druid.query.segmentMetadata.defaultHistory` will be used. https://druid.apache.org/docs/latest/querying/segmentmetadataquery.html#intervals




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