[GitHub] [spark] zsxwing commented on a change in pull request #24173: [SPARK-27237][SS] Introduce State schema validation among query restart

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

zsxwing commented on a change in pull request #24173:
URL: https://github.com/apache/spark/pull/24173#discussion_r528908515



##########
File path: sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/StateSchemaCompatibilityChecker.scala
##########
@@ -0,0 +1,120 @@
+/*
+ * 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.spark.sql.execution.streaming.state
+
+import org.apache.hadoop.conf.Configuration
+import org.apache.hadoop.fs.Path
+
+import org.apache.spark.internal.Logging
+import org.apache.spark.sql.execution.streaming.CheckpointFileManager
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.types.{StructField, StructType}
+
+case class StateSchemaNotCompatible(message: String) extends Exception(message)
+
+class StateSchemaCompatibilityChecker(
+    providerId: StateStoreProviderId,
+    hadoopConf: Configuration) extends Logging {
+
+  private val storeCpLocation = providerId.storeId.storeCheckpointLocation()
+  private val fm = CheckpointFileManager.create(storeCpLocation, hadoopConf)
+  private val schemaFileLocation = schemaFile(storeCpLocation)
+
+  fm.mkdirs(schemaFileLocation.getParent)
+
+  def check(keySchema: StructType, valueSchema: StructType): Unit = {
+    if (fm.exists(schemaFileLocation)) {
+      logDebug(s"Schema file for provider $providerId exists. Comparing with provided schema.")
+      val (storedKeySchema, storedValueSchema) = readSchemaFile()
+
+      def fieldCompatible(fieldOld: StructField, fieldNew: StructField): Boolean = {
+        // compatibility for nullable
+        // - same: OK
+        // - non-nullable -> nullable: OK
+        // - nullable -> non-nullable: Not compatible
+        (fieldOld.dataType == fieldNew.dataType) &&
+          ((fieldOld.nullable == fieldNew.nullable) ||
+            (!fieldOld.nullable && fieldNew.nullable))
+      }
+
+      def schemaCompatible(schemaOld: StructType, schemaNew: StructType): Boolean = {
+        (schemaOld.length == schemaNew.length) &&
+          schemaOld.zip(schemaNew).forall { case (f1, f2) => fieldCompatible(f1, f2) }
+      }
+
+      val errorMsg = "Provided schema doesn't match to the schema for existing state! " +
+        "Please note that Spark allow difference of field name: check count of fields " +
+        "and data type of each field.\n" +
+        s"- provided schema: key $keySchema value $valueSchema\n" +
+        s"- existing schema: key $storedKeySchema value $storedValueSchema\n" +
+        s"If you want to force running query without schema validation, please set " +
+        s"${SQLConf.STATE_SCHEMA_CHECK_ENABLED.key} to false."
+
+      if (storedKeySchema.equals(keySchema) && storedValueSchema.equals(valueSchema)) {
+        // schema is exactly same
+      } else if (!schemaCompatible(storedKeySchema, keySchema) ||
+        !schemaCompatible(storedValueSchema, valueSchema)) {
+        logError(errorMsg)
+        throw StateSchemaNotCompatible(errorMsg)
+      } else {
+        logInfo("Detected schema change which is compatible: will overwrite schema file to new.")
+        // It tries best-effort to overwrite current schema file.
+        // the schema validation doesn't break even it fails, though it might miss on detecting
+        // change which is not a big deal.
+        createSchemaFile(keySchema, valueSchema)
+      }
+    } else {
+      // schema doesn't exist, create one now
+      logDebug(s"Schema file for provider $providerId doesn't exist. Creating one.")
+      createSchemaFile(keySchema, valueSchema)
+    }
+  }
+
+  private def readSchemaFile(): (StructType, StructType) = {
+    val inStream = fm.open(schemaFileLocation)
+    try {
+      val keySchemaStr = inStream.readUTF()
+      val valueSchemaStr = inStream.readUTF()
+
+      (StructType.fromString(keySchemaStr), StructType.fromString(valueSchemaStr))
+    } catch {
+      case e: Throwable =>
+        logError(s"Fail to read schema file from $schemaFileLocation", e)
+        throw e
+    } finally {
+      inStream.close()
+    }
+  }
+
+  private def createSchemaFile(keySchema: StructType, valueSchema: StructType): Unit = {
+    val outStream = fm.createAtomic(schemaFileLocation, overwriteIfPossible = true)
+    try {
+      outStream.writeUTF(keySchema.json)

Review comment:
       Is there any reason to not add version information to this file? The version information would be helpful when we need to change the format in future.




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