Github user squito commented on a diff in the pull request:
https://github.com/apache/spark/pull/7004#discussion_r35796975
--- Diff:
core/src/main/scala/org/apache/spark/serializer/GenericAvroSerializer.scala ---
@@ -0,0 +1,140 @@
+/*
+ * 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.serializer
+
+import java.io.{ByteArrayInputStream, ByteArrayOutputStream}
+import java.nio.ByteBuffer
+
+import scala.collection.mutable
+
+import com.esotericsoftware.kryo.{Kryo, Serializer => KSerializer}
+import com.esotericsoftware.kryo.io.{Input => KryoInput, Output =>
KryoOutput}
+import org.apache.avro.{Schema, SchemaNormalization}
+import org.apache.avro.generic.{GenericData, GenericRecord}
+import org.apache.avro.io._
+import org.apache.commons.io.IOUtils
+
+import org.apache.spark.SparkEnv
+import org.apache.spark.io.CompressionCodec
+
+/**
+ * Custom serializer used for generic Avro records. If the user registers
the schemas
+ * ahead of time, then the schema's fingerprint will be sent with each
message instead of the actual
+ * schema, as to reduce network IO.
+ * Actions like parsing or compressing schemas are computationally
expensive so the serializer
+ * caches all previously seen values as to reduce the amount of work
needed to do.
+ */
+private[serializer] class GenericAvroSerializer(schemas: Map[Long, String])
+ extends KSerializer[GenericRecord] {
+
+ /** Used to reduce the amount of effort to compress the schema */
+ private val compressCache = new mutable.HashMap[Schema, Array[Byte]]()
+ private val decompressCache = new mutable.HashMap[ByteBuffer, Schema]()
+
+ /** Reuses the same datum reader/writer since the same schema will be
used many times */
+ private val writerCache = new mutable.HashMap[Schema, DatumWriter[_]]()
+ private val readerCache = new mutable.HashMap[Schema, DatumReader[_]]()
+
+ /** Fingerprinting is very expensive so this alleviates most of the work
*/
+ private val fingerprintCache = new mutable.HashMap[Schema, Long]()
+ private val schemaCache = new mutable.HashMap[Long, Schema]()
+
+ /** This needs to be lazy since SparkEnv is not initialized yet
sometimes when this is called */
+ private lazy val codec = CompressionCodec.createCodec(SparkEnv.get.conf)
--- End diff --
for anybody that is curious -- I had gotten myself pretty confused about
why this change would make the `SparkConf` serialized. `KryoSerializer`
already had a `conf` argument to the constructor, that wasn't changed. But the
`conf` there is only accessed in field initialization, never in methods, so it
wasn't stored. But through the wonders of scala, when you access that `conf`
in a method, suddenly `conf` also becomes a member variable, and now you can no
longer serialize the `KryoSerializer`.
In practice this means the `lazy val codec` here is fine in actual use, but
it could be very confusing in a unit test where the `SparkEnv` hasn't been set.
So I'll add comment explaining this a bit.
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