[GitHub] [kafka] ijuma commented on a change in pull request #8467: MINOR: reduce allocations in log start and recovery checkpoints

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

ijuma commented on a change in pull request #8467:
URL: https://github.com/apache/kafka/pull/8467#discussion_r413826884



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File path: core/src/main/scala/kafka/log/LogManager.scala
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@@ -1003,9 +1003,17 @@ class LogManager(logDirs: Seq[File],
   /**
    * Map of log dir to logs by topic and partitions in that dir
    */
-  private def logsByDir: Map[String, Map[TopicPartition, Log]] = {
-    (this.currentLogs.toList ++ this.futureLogs.toList).toMap
-      .groupBy { case (_, log) => log.parentDir }
+  def logsByDir: Map[String, Map[TopicPartition, Log]] = {
+    // This code is called often by checkpoint processes and is written in a way that reduces
+    // allocations and CPU with many topic partitions.
+    // When changing this code please measure the changes with org.apache.kafka.jmh.server.CheckpointBench
+    val byDir = new mutable.AnyRefMap[String, mutable.AnyRefMap[TopicPartition, Log]]()
+    def addToDir(tp: TopicPartition, log: Log): Unit = {
+      byDir.getOrElseUpdate(log.parentDir, new mutable.AnyRefMap[TopicPartition, Log]()).put(tp, log)
+    }
+    currentLogs.foreach { case (tp, log) => addToDir(tp, log) }
+    futureLogs.foreach { case (tp, log) => addToDir(tp, log) }

Review comment:
       `scala.collection.Map` has a `def foreachEntry[U](f: (K, V) => U): Unit` method that avoids allocating tuples (it's a function with two parameters). If we want to avoid allocations, we should introduce one such method to `Pool` and use it here.




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