[GitHub] twalthr commented on a change in pull request #6776: [FLINK-9715][table] Support temporal join with event time

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twalthr commented on a change in pull request #6776: [FLINK-9715][table] Support temporal join with event time
URL: https://github.com/apache/flink/pull/6776#discussion_r221583273
 
 

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 File path: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/runtime/join/TemporalRowtimeJoin.scala
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+/*
+ * 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.flink.table.runtime.join
+
+import java.lang.{Long => JLong}
+import java.util
+import java.util.Comparator
+
+import org.apache.flink.api.common.functions.FlatJoinFunction
+import org.apache.flink.api.common.state._
+import org.apache.flink.api.common.typeinfo.{BasicTypeInfo, TypeInformation}
+import org.apache.flink.runtime.state.{VoidNamespace, VoidNamespaceSerializer}
+import org.apache.flink.streaming.api.SimpleTimerService
+import org.apache.flink.streaming.api.operators._
+import org.apache.flink.streaming.runtime.streamrecord.StreamRecord
+import org.apache.flink.table.api.{StreamQueryConfig, TableException}
+import org.apache.flink.table.codegen.Compiler
+import org.apache.flink.table.runtime.CRowWrappingCollector
+import org.apache.flink.table.runtime.types.CRow
+import org.apache.flink.table.typeutils.TypeCheckUtils._
+import org.apache.flink.table.util.Logging
+import org.apache.flink.types.Row
+
+import scala.collection.JavaConversions._
+
+/**
+  * This operator works by keeping on the state collection of probe and build records to process
+  * on next watermark. The idea is that between watermarks we are collecting those elements
+  * and once we are sure that there will be no updates we emit the correct result and clean up the
+  * state.
+  *
+  * Cleaning up the state drops all of the "old" values from the probe side, where "old" is defined
+  * as older then the current watermark. Build side is also cleaned up in the similar fashion,
+  * however we always keep at least one record - the latest one - even if it's past the last
+  * watermark.
+  *
+  * One more trick is how the emitting results and cleaning up is triggered. It is achieved
+  * by registering timers for the keys. We could register a timer for every probe and build
+  * side element's event time (when watermark exceeds this timer, that's when we are emitting and/or
+  * cleaning up the state). However this would cause huge number of registered timers. For example
+  * with following evenTimes of probe records accumulated: {1, 2, 5, 8, 9}, if we
+  * had received Watermark(10), it would trigger 5 separate timers for the same key. To avoid that
+  * we always keep only one single registered timer for any given key, registered for the minimal
+  * value. Upon triggering it, we process all records with event times older then currentWatermark.
+  */
+class TemporalRowtimeJoin(
+    leftType: TypeInformation[Row],
+    rightType: TypeInformation[Row],
+    genJoinFuncName: String,
+    genJoinFuncCode: String,
+    queryConfig: StreamQueryConfig,
+    leftTimeAttribute: Int,
+    rightTimeAttribute: Int)
+  extends AbstractStreamOperator[CRow]
+  with TwoInputStreamOperator[CRow, CRow, CRow]
+  with Triggerable[Any, VoidNamespace]
+  with Compiler[FlatJoinFunction[Row, Row, Row]]
+  with Logging {
+
+  validateEqualsHashCode("join", leftType)
+  validateEqualsHashCode("join", rightType)
+
+  private val netLeftIndexStateName = "next-index"
+  private val leftStateName = "left"
+  private val rightStateName = "right"
+  private val registeredTimerStateName = "timer"
+  private val probteTimersStateName = "probe-timers"
 
 Review comment:
   btw I find the mixture of left/right, probe/build confusing. Maybe call this `rightTimersStateName` instead?

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