[GitHub] [kafka] mimaison commented on a change in pull request #8569: KIP-551: Expose disk read and write metrics

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mimaison commented on a change in pull request #8569:
URL: https://github.com/apache/kafka/pull/8569#discussion_r421525324



##########
File path: core/src/main/scala/kafka/metrics/LinuxIoMetricsCollector.scala
##########
@@ -0,0 +1,96 @@
+/**
+ * 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 kafka.server
+
+import java.nio.file.{Files, Paths}
+
+import org.apache.kafka.common.utils.Time
+import org.slf4j.Logger
+
+import scala.jdk.CollectionConverters._
+
+/**
+ * Retrieves Linux /proc/self/io metrics.
+ */
+class LinuxIoMetricsCollector(val procPath: String, val time: Time, val logger: Logger) {
+  import LinuxIoMetricsCollector._
+  var lastUpdateMs = -1L
+  var cachedReadBytes = 0L
+  var cachedWriteBytes = 0L
+
+  def readBytes(): Long = this.synchronized {
+    val curMs = time.milliseconds()
+    if (curMs != lastUpdateMs) {

Review comment:
       Should we have add small jitter to `lastUpdateMs` as both metrics should trigger around the same time, ie
   ```
   if (curMs > lastUpdateMs + 100) {
   ```

##########
File path: core/src/main/scala/kafka/metrics/LinuxIoMetricsCollector.scala
##########
@@ -0,0 +1,96 @@
+/**
+ * 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 kafka.server
+
+import java.nio.file.{Files, Paths}
+
+import org.apache.kafka.common.utils.Time
+import org.slf4j.Logger
+
+import scala.jdk.CollectionConverters._
+
+/**
+ * Retrieves Linux /proc/self/io metrics.
+ */
+class LinuxIoMetricsCollector(val procPath: String, val time: Time, val logger: Logger) {
+  import LinuxIoMetricsCollector._
+  var lastUpdateMs = -1L
+  var cachedReadBytes = 0L
+  var cachedWriteBytes = 0L
+
+  def readBytes(): Long = this.synchronized {
+    val curMs = time.milliseconds()
+    if (curMs != lastUpdateMs) {
+      updateValues(curMs)
+    }
+    cachedReadBytes
+  }
+
+  def writeBytes(): Long = this.synchronized {
+    val curMs = time.milliseconds()
+    if (curMs != lastUpdateMs) {
+      updateValues(curMs)
+    }
+    cachedWriteBytes
+  }
+
+  /**
+   * Read /proc/self/io.
+   *
+   * Generally, each line in this file contains a prefix followed by a colon and a number.
+   *
+   * For example, it might contain this:
+   * rchar: 4052
+   * wchar: 0
+   * syscr: 13
+   * syscw: 0
+   * read_bytes: 0
+   * write_bytes: 0
+   * cancelled_write_bytes: 0
+   */
+  def updateValues(now: Long): Boolean = this.synchronized {
+    try {
+      cachedReadBytes = -1
+      cachedWriteBytes = -1
+      val lines = Files.readAllLines(Paths.get(procPath, "self", "io")).asScala
+      lines.foreach(line => {
+        if (line.startsWith(READ_BYTES_PREFIX)) {
+          cachedReadBytes = line.substring(READ_BYTES_PREFIX.size).toLong
+        } else if (line.startsWith(WRITE_BYTES_PREFIX)) {
+          cachedWriteBytes = line.substring(WRITE_BYTES_PREFIX.size).toLong
+        }
+      })
+      lastUpdateMs = now
+      true
+    } catch {
+      case t: Throwable => {
+        logger.warn("LinuxIoMetricsCollector: unable to update metrics", t)
+        false
+      }
+    }
+  }
+
+  def usable(): Boolean = {
+    updateValues(time.milliseconds())

Review comment:
       This prints a stacktrace at startup when not on Linux. I wonder if we should check if `/proc` exists and only print a stacktrace if it exists and we can't read it. WDYT?




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