Kafka除錯入門(一)

田野與天發表於2021-02-03

很多人對kafka訊息佇列應該不陌生,使用起來也比較方便。對kafka最常見的操作一般有如下幾種:

  1. 啟動kafka叢集
  2. 建立一個名稱為xxx的主題(topic)
  3. 檢視已經建立好的主題
  4. 向xxx這個主題中插入一些資料
  5. 從xxx這個主題中消費一些資料
針對這幾種操作,其實kafka都為大家提供了一系列方便使用的指令碼,這些指令碼都在bin資料夾中,主要有

 

  • bin/kafka-server-start.sh   //作用是啟動kafka服務端程式
  • bin/kafka-topics.sh    //作用是建立、檢視主題 
  • bin/kafka-console-producer.sh    //命令列方式的生產者
  • bin/kafka-console-consumer.sh    //命令列方式的消費者

 

下面是一些常用的操作例項:

  • 啟動kafka叢集:
    bin/kafka-server-start.sh config/server.properties
  • 建立一個名稱是test的主體(topic)
    bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic test
  • 檢視建立的主題(topic)
    bin/kafka-topics.sh --list --zookeeper localhost:2181
  • 往test這個topic中插入一些資料,用kafka-console-producer
    bin/kafka-console-producer.sh --broker-list localhost:9092 --topic test
  • 從test這個topic中消費一些資料,用kafka-console-consumer從最開頭開始讀取資料:
    bin/kafka-console-consumer.sh --bootstrap-server localhost:9092 --topic test --from-beginning
 

 正文

kafka-server-start.sh執行流程分析

首先分析一下執行bin/kafka-server-start.sh config/server.properties的時候,kafka原始碼的執行流程。

第一步:先看看kafka-server-start.sh這個指令碼,如下

 

#!/bin/bash
# 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.

# 此處是判斷一下執行kafka-server-start.sh 這個指令碼後邊的引數的個數,
# 如果小於1,那麼說明沒有傳入server.properties這個檔案的路徑,
# 那就列印使用說明給使用者並直接退出,不繼續執行後續的指令碼。
if [ $# -lt 1 ];
then
	echo "USAGE: $0 [-daemon] server.properties [--override property=value]*"
	exit 1
fi

#該指令碼所在的資料夾的路徑,例如:/data/kafka/bin/
base_dir=$(dirname $0)



# 檢查KAFKA_LOG4J_OPTS這個變數是否已經被設定
# 如果沒有,就設定為 
# -Dlog4j.configuration=file:$base_dir/../config/log4j.properties
# 其中的$base_dir會被替換為真實路徑
# 假設base_dir是/data/kafka/bin/的話
# KAFKA_LOG4J_OPTS=
# "-Dlog4j.configuration=file:/data/kafka/bin/../config/log4j.properties"

if [ "x$KAFKA_LOG4J_OPTS" = "x" ]; then
    export KAFKA_LOG4J_OPTS="-Dlog4j.configuration=file:$base_dir/../config/log4j.properties"
fi


# 檢查KAFKA_HEAP_OPTS這個變數是否已經被設定
# 如果沒有的話,就設定為
# -Xmx1G -Xms1G
# 即 KAFKA_HEAP_OPTS="-Xmx1G -Xms1G"

if [ "x$KAFKA_HEAP_OPTS" = "x" ]; then
    export KAFKA_HEAP_OPTS="-Xmx1G -Xms1G"
fi



# EXTRA_ARGS="-name kafkaServer -loggc"
EXTRA_ARGS=${EXTRA_ARGS-'-name kafkaServer -loggc'}

# $1是執行指令碼時的第一個引數,比如
# sh 1.sh a b c
# 那麼$1='a'   $2='b'  $3='c'
# 所以此處是檢查執行kafka-server-start.sh 這個指令碼的時候,第一個引數是不是-daemon
# 假設我執行的是./kafka-server-start.sh -daemon ../conf/server.properties
# 那麼就會進入下面的   -daemon)  分支
# 假設我執行的是./kafka-server-start.sh  ../conf/server.properties
# 那麼就會進入到下面的   *)   分支
# -daemon  分支做的事情是 給EXTRA_ARGS這個變數再追加一個引數,
# 原來EXTRA_ARGS="-name kafkaServer -loggc",
# 追加後變成了"-daemon -name kafkaServer -loggc"

COMMAND=$1
case $COMMAND in
  -daemon)
    EXTRA_ARGS="-daemon "$EXTRA_ARGS
    shift
    ;;
  *)
    ;;
esac

#最後執行程式啟動kafka server
# 可以把exec改成 echo 列印出來看看 下面的指令碼都被替換成啥了
# 我本機輸出了 bin/kafka-run-class.sh -name kafkaServer -loggc kafka.Kafka -deamon config/server.properties
#也就是說其實最後執行的是 bin/kafka-run-class.sh -name kafkaServer -loggc kafka.Kafka -deamon config/server.properties

exec $base_dir/kafka-run-class.sh $EXTRA_ARGS kafka.Kafka "$@"

  

兜兜轉轉,我們發現我執行的

bin/kafka-server-start.sh -daemon conf/server.properties

最後在kafka-server-start.sh指令碼里面進行一番轉換之後變成了

bin/kafka-run-class.sh -name kafkaServer -loggc kafka.Kafka -deamon config/server.properties

那麼接著我們就開始分析bin/kafka-run-class.sh這個指令碼,還是貼一下這個指令碼完整程式碼,再結合程式碼做一些解釋。

 

#!/bin/bash
# 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.

#如果引數的個數小於1,進入if條件
if [ $# -lt 1 ];
then
  #列印該指令碼的使用方式給使用者。
  echo "USAGE: $0 [-daemon] [-name servicename] [-loggc] classname [opts]"
  exit 1
fi

# 執行一下linux命令 uname -a ,看一下的結果中是不是有“CYGWIN”字串
if [[ $(uname -a) =~ "CYGWIN" ]]; then
  #如果有的話,就把CYGWIN設定為1
  CYGWIN=1
else
  #如果沒有匹配到“CYGWIN”字串,則把CYGWIN設定為0
  CYGWIN=0
fi

# 判斷一下$INCLUDE_TEST_JARS變數的值,是否為空;是的話進入if中
if [ -z "$INCLUDE_TEST_JARS" ]; then
  #把INCLUDE_TEST_JARS設定為false
  INCLUDE_TEST_JARS=false
fi

#一個用來匹配測試用的jar包的正規表示式
regex="(-(test|test-sources|src|scaladoc|javadoc)\.jar|jar.asc)$"

#一個函式,用來判斷一個檔案是不是測試相關的或者文件相關的。
#如果傳入的檔案是測試相關的,返回0
#如果傳入的是與執行程式息息相關的,重要的,則返回1
should_include_file() {
  if [ "$INCLUDE_TEST_JARS" = true ]; then
    return 0
  fi
  file=$1
  if [ -z "$(echo "$file" | egrep "$regex")" ] ; then
    return 0
  else
    return 1
  fi
}

#設定base_dir為當前指令碼bin資料夾的上一級目錄。
#比如我的kafka-run-class.sh路徑是/data/kafka2.2/bin/,那麼base_dir就是/data/kafka2.2/
base_dir=$(dirname $0)/..

# 判斷一下$SCALA_VERSION變數的值,是否為空;是的話進入if中
if [ -z "$SCALA_VERSION" ]; then
  #設定$SCALA_VERSION為2.13.2
  SCALA_VERSION=2.13.2
  #判斷一下base_dir目錄下是不是有gradle.properties檔案,如果有的話,進入if邏輯塊
  if [[ -f "$base_dir/gradle.properties" ]]; then
    #設定SCALA_VERSION變數為從gradle.properties中查詢到的值,比如gradle.properties中可能有一行scalaVersion=2.11.1
    #那麼用cut切掉等號左邊的部分,剩下2.11.1。把2.11.1設定到
    SCALA_VERSION=`grep "^scalaVersion=" "$base_dir/gradle.properties" | cut -d= -f 2`
  fi
fi

# 判斷一下$SCALA_BINARY_VERSION內容的長度是不是0,是則進入if
if [ -z "$SCALA_BINARY_VERSION" ]; then
  #設定SCALA_BINARY_VERSION變數的值為SCALA_VERSION的前三分之二。
  #比如SCALA_VERSION=2.11.1   那麼SCALA_BINARY_VERSION=2.11
  SCALA_BINARY_VERSION=$(echo $SCALA_VERSION | cut -f 1-2 -d '.')
fi
done

#這裡設定nullglob開啟,這個nullglob開啟之後,shell指令碼或者終端中可以識別萬用字元*,關閉後不能用*這個萬用字元
shopt -s nullglob

# 判斷一下$UPGRADE_KAFKA_STREAMS_TEST_VERSION變數的值,是否為空;是的話進入if中
if [ -z "$UPGRADE_KAFKA_STREAMS_TEST_VERSION" ]; then
  #依次把base_dir/core/build/資料夾下dependant-libs-${SCALA_VERSION}開頭的資料夾路徑 賦值給 dir變數
  for dir in "$base_dir"/core/build/dependant-libs-${SCALA_VERSION}*;
  do
    #把dir變數的內容追加到$CLASSPATH中
    CLASSPATH="$CLASSPATH:$dir/*"
  done
fi

#依次把base_dir/examples/build/libs/資料夾下kafka-examples開頭,.jar結尾的檔案全路徑(含檔名稱) 賦值給 file變數
for file in "$base_dir"/examples/build/libs/kafka-examples*.jar;
do
  #判斷一下,如果should_include_file返回1,也就是說是重要的jar包,就進入到if邏輯
  if should_include_file "$file"; then
    #新增$file變數的內容到$CLASSPATH中
    CLASSPATH="$CLASSPATH":"$file"
  fi
done


# 判斷一下$UPGRADE_KAFKA_STREAMS_TEST_VERSION變數的值,是否為空;是的話進入if中
if [ -z "$UPGRADE_KAFKA_STREAMS_TEST_VERSION" ]; then
  #設定clients_lib_dir為    當期指令碼所在目錄/../clients/build/libs
  clients_lib_dir=$(dirname $0)/../clients/build/libs
  #設定streams_lib_dir為    當期指令碼所在目錄/../streams/build/libs
  streams_lib_dir=$(dirname $0)/../streams/build/libs
  #設定streams_dependant_clients_lib_dir為    當期指令碼所在目錄/../streams/build/dependant-libs-${SCALA_VERSION}
  streams_dependant_clients_lib_dir=$(dirname $0)/../streams/build/dependant-libs-${SCALA_VERSION}
else
  #設定clients_lib_dir為    /opt/kafka-$UPGRADE_KAFKA_STREAMS_TEST_VERSION/libs
  clients_lib_dir=/opt/kafka-$UPGRADE_KAFKA_STREAMS_TEST_VERSION/libs
  #設定streams_lib_dir為    和clients_lib_dir一樣
  streams_lib_dir=$clients_lib_dir
  #設定streams_dependant_clients_lib_dir為    和clients_lib_dir一樣
  streams_dependant_clients_lib_dir=$streams_lib_dir
fi

#依次把$clients_lib_dir資料夾下kafka-clients開頭,.jar結尾的檔案全路徑(含檔名稱) 賦值給 file變數
for file in "$clients_lib_dir"/kafka-clients*.jar;
do
  #判斷一下,如果should_include_file返回1,也就是說是重要的jar包,就進入到if邏輯
  if should_include_file "$file"; then
    #新增$file變數的內容到$CLASSPATH中
    CLASSPATH="$CLASSPATH":"$file"
  fi
done

#依次把$streams_lib_dir資料夾下kafka-streams開頭,.jar結尾的檔案全路徑(含檔名稱) 賦值給 file變數
for file in "$streams_lib_dir"/kafka-streams*.jar;
do
  #判斷一下,如果should_include_file返回1,也就是說是重要的jar包,就進入到if邏輯
  if should_include_file "$file"; then
    #新增$file變數的內容到$CLASSPATH中
    CLASSPATH="$CLASSPATH":"$file"
  fi
done

# 判斷一下$UPGRADE_KAFKA_STREAMS_TEST_VERSION變數的內容的長度是否為0,是則進入
if [ -z "$UPGRADE_KAFKA_STREAMS_TEST_VERSION" ]; then
  #依次把base_dir/streams/examples/build/libs/資料夾下kafka-streams-examples開頭,.jar結尾的檔案全路徑(含檔名稱) 賦值給 file變數
  for file in "$base_dir"/streams/examples/build/libs/kafka-streams-examples*.jar;
  do
    #判斷一下,如果should_include_file返回1,也就是說是重要的jar包,就進入到if邏輯
    if should_include_file "$file"; then
      #新增$file變數的內容到$CLASSPATH中
      CLASSPATH="$CLASSPATH":"$file"
    fi
  done
else
  #替換$UPGRADE_KAFKA_STREAMS_TEST_VERSION中的小數點,比如$UPGRADE_KAFKA_STREAMS_TEST_VERSION=2.12.1
  #替換後變成2121
  VERSION_NO_DOTS=`echo $UPGRADE_KAFKA_STREAMS_TEST_VERSION | sed 's/\.//g'`
  #SHORT_VERSION_NO_DOTS等於VERSION_NO_DOTS剔除最後一位,比如VERSION_NO_DOTS等於2121  SHORT_VERSION_NO_DOTS等於212
  SHORT_VERSION_NO_DOTS=${VERSION_NO_DOTS:0:((${#VERSION_NO_DOTS} - 1))} # remove last char, ie, bug-fix number
  #依次把base_dir/streams/upgrade-system-tests-$SHORT_VERSION_NO_DOTS/build/libs/資料夾下
  #kafka-streams-upgrade-system-tests開頭,.jar結尾的檔案全路徑(含檔名稱) 賦值給 file變數
  for file in "$base_dir"/streams/upgrade-system-tests-$SHORT_VERSION_NO_DOTS/build/libs/kafka-streams-upgrade-system-tests*.jar;
  do
    #判斷一下,如果should_include_file返回1,也就是說是重要的jar包,就進入到if邏輯
    if should_include_file "$file"; then
      #新增$file變數的內容到$CLASSPATH中
      CLASSPATH="$file":"$CLASSPATH"
    fi
  done
  #如果$SHORT_VERSION_NO_DOTS等於0100,
  if [ "$SHORT_VERSION_NO_DOTS" = "0100" ]; then
    #追加/opt/kafka-$UPGRADE_KAFKA_STREAMS_TEST_VERSION/libs/zkclient-0.8.jar到classpath
    CLASSPATH="/opt/kafka-$UPGRADE_KAFKA_STREAMS_TEST_VERSION/libs/zkclient-0.8.jar":"$CLASSPATH"
    #追加/opt/kafka-$UPGRADE_KAFKA_STREAMS_TEST_VERSION/libs/zookeeper-3.4.6.jar到classpath
    CLASSPATH="/opt/kafka-$UPGRADE_KAFKA_STREAMS_TEST_VERSION/libs/zookeeper-3.4.6.jar":"$CLASSPATH"
  fi
  #如果$SHORT_VERSION_NO_DOTS等於0101
  if [ "$SHORT_VERSION_NO_DOTS" = "0101" ]; then
    #追加/opt/kafka-$UPGRADE_KAFKA_STREAMS_TEST_VERSION/libs/zkclient-0.9.jar到classpath
    CLASSPATH="/opt/kafka-$UPGRADE_KAFKA_STREAMS_TEST_VERSION/libs/zkclient-0.9.jar":"$CLASSPATH"
    #追加/opt/kafka-$UPGRADE_KAFKA_STREAMS_TEST_VERSION/libs/zookeeper-3.4.8.jar到classpath
    CLASSPATH="/opt/kafka-$UPGRADE_KAFKA_STREAMS_TEST_VERSION/libs/zookeeper-3.4.8.jar":"$CLASSPATH"
  fi
fi

#遍歷$streams_dependant_clients_lib_dir資料夾下的rocksdb開頭,.jar結尾的檔案
for file in "$streams_dependant_clients_lib_dir"/rocksdb*.jar;
do
  #依次新增檔案到classpath中
  CLASSPATH="$CLASSPATH":"$file"
done

#遍歷$streams_dependant_clients_lib_dir資料夾下的中間匹配hamcrest字串,.jar結尾的檔案
for file in "$streams_dependant_clients_lib_dir"/*hamcrest*.jar;
do
  CLASSPATH="$CLASSPATH":"$file"
done

#遍歷$streams_dependant_clients_lib_dir資料夾下的kafka-tools開頭,.jar結尾的檔案
for file in "$base_dir"/tools/build/libs/kafka-tools*.jar;
do
  #判斷一下,如果should_include_file返回1,也就是說是重要的jar包,就進入到if邏輯
  if should_include_file "$file"; then
    #新增$file變數的內容到$CLASSPATH中
    CLASSPATH="$CLASSPATH":"$file"
  fi
done

#依次把base_dir/tools/build/資料夾下dependant-libs-${SCALA_VERSION}開頭的資料夾路徑 賦值給 dir變數
for dir in "$base_dir"/tools/build/dependant-libs-${SCALA_VERSION}*;
do
  #新增$file變數的內容到$CLASSPATH中
  CLASSPATH="$CLASSPATH:$dir/*"
done

#依次把 "api" "transforms" "runtime" "file" "mirror" "mirror-client" "json" "tools" "basic-auth-extension" 逐個賦值給cc_pkg變數
for cc_pkg in "api" "transforms" "runtime" "file" "mirror" "mirror-client" "json" "tools" "basic-auth-extension"
do
  #遍歷$base_dir/connect/${cc_pkg}/build/libs/資料夾下的connect-${cc_pkg}開頭,.jar結尾的檔案
  for file in "$base_dir"/connect/${cc_pkg}/build/libs/connect-${cc_pkg}*.jar;
  do
    #判斷一下,如果should_include_file返回1,也就是說是重要的jar包,就進入到if邏輯
    if should_include_file "$file"; then
      #新增$file變數的內容到$CLASSPATH中
      CLASSPATH="$CLASSPATH":"$file"
    fi
  done
  #判斷$base_dir/connect/${cc_pkg}/build/dependant-libs資料夾是否存在,是的話進入if
  if [ -d "$base_dir/connect/${cc_pkg}/build/dependant-libs" ] ; then
    #把base_dir/connect/${cc_pkg}/build/dependant-libs/下的所有檔案都加入到classpath中去
    CLASSPATH="$CLASSPATH:$base_dir/connect/${cc_pkg}/build/dependant-libs/*"
  fi
done

# 遍歷base_dir資料夾下的libs
for file in "$base_dir"/libs/*;
do
  #判斷一下,如果should_include_file返回1,也就是說是重要的jar包,就進入到if邏輯
  if should_include_file "$file"; then
    #新增$file變數的內容到$CLASSPATH中
    CLASSPATH="$CLASSPATH":"$file"
  fi
done

#遍歷base_dir/core/build/libs/資料夾下所有kafka_${SCALA_BINARY_VERSION}開頭的檔案
for file in "$base_dir"/core/build/libs/kafka_${SCALA_BINARY_VERSION}*.jar;
do
  #判斷一下,如果should_include_file返回1,也就是說是重要的jar包,就進入到if邏輯
  if should_include_file "$file"; then
    #新增$file變數的內容到$CLASSPATH中
    CLASSPATH="$CLASSPATH":"$file"
  fi
done
#到此關閉nullglob,也就是說後邊用不到*去匹配檔案和資料夾了
shopt -u nullglob


#判斷$CLASSPATH的內容長度是不是0,是則為真
if [ -z "$CLASSPATH" ] ; then
  #列印錯誤資訊
  echo "Classpath is empty. Please build the project first e.g. by running './gradlew jar -PscalaVersion=$SCALA_VERSION'"
  #退出指令碼,不再向下繼續執行
  exit 1
fi

#判斷$KAFKA_JMX_OPTS的內容長度是不是0,是則為真
if [ -z "$KAFKA_JMX_OPTS" ]; then
  #設定KAFKA_JMX_OPTS的值為-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.authenticate=false  -Dcom.sun.management.jmxremote.ssl=false
  KAFKA_JMX_OPTS="-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.authenticate=false  -Dcom.sun.management.jmxremote.ssl=false "
fi

#判斷$JMX_PORT是不是空的,空的話就進入if塊
if [  $JMX_PORT ]; then
  #設定KAFKA_JMX_OPTS的值為 $KAFKA_JMX_OPTS -Dcom.sun.management.jmxremote.port=$JMX_PORT
  KAFKA_JMX_OPTS="$KAFKA_JMX_OPTS -Dcom.sun.management.jmxremote.port=$JMX_PORT "
fi

#判斷$LOG_DIR是不是空的,空的話就進入if塊
if [ "x$LOG_DIR" = "x" ]; then
  #LOG_DIR=$base_dir/log
  LOG_DIR="$base_dir/logs"
fi

#判斷$KAFKA_LOG4J_OPTS內容的長度是不是0,是則為真
if [ -z "$KAFKA_LOG4J_OPTS" ]; then
  #設定LOG4J_DIR為$base_dir/config/tools-log4j.properties
  LOG4J_DIR="$base_dir/config/tools-log4j.properties"
  # 如果檢測到CYGWIN,那麼需要轉換LOG4J_DIR中的path
  (( CYGWIN )) && LOG4J_DIR=$(cygpath --path --mixed "${LOG4J_DIR}")
  #設定KAFKA_LOG4J_OPTS為 -Dlog4j.configuration=file:${LOG4J_DIR}
  KAFKA_LOG4J_OPTS="-Dlog4j.configuration=file:${LOG4J_DIR}"
else
  # 如果不存在$LOG_DIR這個資料夾,那麼就建立一個資料夾
  if [ ! -d "$LOG_DIR" ]; then
    mkdir -p "$LOG_DIR"
  fi
fi

# 如果檢測到CYGWIN,那麼需要轉換LOG_DIR中的path
(( CYGWIN )) && LOG_DIR=$(cygpath --path --mixed "${LOG_DIR}")
KAFKA_LOG4J_OPTS="-Dkafka.logs.dir=$LOG_DIR $KAFKA_LOG4J_OPTS"

# 判斷$KAFKA_OPTS這個變數內容長度為0,則為真
if [ -z "$KAFKA_OPTS" ]; then
  #如果為空,設定為""
  KAFKA_OPTS=""
fi

#如果$KAFKA_DEBUG的內容為空
if [ "x$KAFKA_DEBUG" != "x" ]; then

    # 設定DEFAULT_JAVA_DEBUG_PORT變數為5005
    DEFAULT_JAVA_DEBUG_PORT="5005"

    #如果$JAVA_DEBUG_PORT的長度為0,則為真
    if [ -z "$JAVA_DEBUG_PORT" ]; then
        #設定JAVA_DEBUG_PORT為$DEFAULT_JAVA_DEBUG_PORT
        JAVA_DEBUG_PORT="$DEFAULT_JAVA_DEBUG_PORT"
    fi

    # DEFAULT_JAVA_DEBUG_OPTS設定為-agentlib:jdwp=transport=dt_socket,server=y,suspend=${DEBUG_SUSPEND_FLAG:-n},address=$JAVA_DEBUG_PORT
    DEFAULT_JAVA_DEBUG_OPTS="-agentlib:jdwp=transport=dt_socket,server=y,suspend=${DEBUG_SUSPEND_FLAG:-n},address=$JAVA_DEBUG_PORT"
    # 檢查$JAVA_DEBUG_OPTS的內容是不是長度為0,是則進入if
    if [ -z "$JAVA_DEBUG_OPTS" ]; then
        #設定JAVA_DEBUG_OPTS的值等於$DEFAULT_JAVA_DEBUG_OPTS
        JAVA_DEBUG_OPTS="$DEFAULT_JAVA_DEBUG_OPTS"
    fi

    #列印 Enabling Java debug options: $JAVA_DEBUG_OPTS 到螢幕
    echo "Enabling Java debug options: $JAVA_DEBUG_OPTS"
    #設定KAFKA_OPTS的變數值為 $JAVA_DEBUG_OPTS 拼接上$KAFKA_OPTS
    KAFKA_OPTS="$JAVA_DEBUG_OPTS $KAFKA_OPTS"
fi

#判斷一下使用那個JAVA_HOME
#首先判斷JAVA_HOME這個變數的內容的長度是不是0,是則進入if
if [ -z "$JAVA_HOME" ]; then
  #設定JAVA變數的值為"JAVA"
  JAVA="java"
else
  #設定JAVA變數的值為$JAVA_HOME/bin/java
  JAVA="$JAVA_HOME/bin/java"
fi

#設定記憶體相關的引數
#首先判斷一下$KAFKA_HEAP_OPTS變數內容的長度是不是0,是則進入if
if [ -z "$KAFKA_HEAP_OPTS" ]; then
  #設定KAFKA_HEAP_OPTS的值為 -Xmx256M
  KAFKA_HEAP_OPTS="-Xmx256M"
fi

# JVM效能引數
# MaxInlineLevel=15是自JDK 14以來的預設值,一旦不再支援舊版JDK,就可以刪除。
#首先判斷一下$KAFKA_JVM_PERFORMANCE_OPTS變數內容的長度是不是0,是則進入if
if [ -z "$KAFKA_JVM_PERFORMANCE_OPTS" ]; then
  #設定KAFKA_JVM_PERFORMANCE_OPTS的值為-server -XX:+UseG1GC -XX:MaxGCPauseMillis=20 -XX:InitiatingHeapOccupancyPercent=35 -XX:+ExplicitGCInvokesConcurrent -XX:MaxInlineLevel=15 -Djava.awt.headless=true
  KAFKA_JVM_PERFORMANCE_OPTS="-server -XX:+UseG1GC -XX:MaxGCPauseMillis=20 -XX:InitiatingHeapOccupancyPercent=35 -XX:+ExplicitGCInvokesConcurrent -XX:MaxInlineLevel=15 -Djava.awt.headless=true"
fi

#首先$#代表的是指令碼後邊的引數的個數
#-gt是 greater  than 的縮寫,代表的意思是 大於
#判斷一下引數的個數是不是大於0,是則進入
while [ $# -gt 0 ]; do
  #設定COMMAND的值為第一個引數
  COMMAND=$1
  # 判斷COMMAND的內容
  case $COMMAND in
    #如果COMMAND的內容為-name
    -name)
      #設定DAEMON_NAME的值為緊隨COMMAND後邊的第二個引數
      DAEMON_NAME=$2
      #設定CONSOLE_OUTPUT_FILE的值為$LOG_DIR/$DAEMON_NAME.out
      CONSOLE_OUTPUT_FILE=$LOG_DIR/$DAEMON_NAME.out
      #剔除原來的前2個引數,把原來的第三個引數變為第一個引數,原來的第四個引數變為第二個引數
      shift 2
      ;;
    #如果COMMAND的內容為-loggc
    -loggc)
      #判斷$KAFKA_GC_LOG_OPTS,如果$KAFKA_GC_LOG_OPTS的內容長度為0,則進入if
      if [ -z "$KAFKA_GC_LOG_OPTS" ]; then
        #GC_LOG_ENABLED的值設定為true
        GC_LOG_ENABLED="true"
      fi
      #剔除原來的1個引數,把原來的第二個引數變為第一個引數,原來的第三個引數變為第二個引數
      shift
      ;;
    #如果COMMAND的內容為-daemon
    -daemon)
      #設定DAEMON_MODE的值為true
      DAEMON_MODE="true"
      #剔除原來的1個引數,把原來的第二個引數變為第一個引數,原來的第三個引數變為第二個引數
      shift
      ;;
    *)
      break
      ;;
  esac
done

# GC相關的引數設定
#設定GC_FILE_SUFFIX的值為-gc.log
#設定GC_LOG_FILE_NAME的指為''
GC_FILE_SUFFIX='-gc.log'
GC_LOG_FILE_NAME=''
#如果GC_LOG_ENABLED的值等於true的話
if [ "x$GC_LOG_ENABLED" = "xtrue" ]; then
  #GC_LOG_FILE_NAME的值設定為$DAEMON_NAME追加$GC_FILE_SUFFIX
  GC_LOG_FILE_NAME=$DAEMON_NAME$GC_FILE_SUFFIX

  # 版本號的第一段,對於Java 9之前的版本來說是 "1"。
  # 然後變成'9', '10', ...
  # `java --version`第一行的一些例子。
  # 8 -> java版本 "1.8.0_152"
  # 9.0.4 ->java版本 "9.0.4"
  # 10 ->java版本 "10" 2018-03-20
  # 10.0.1 -> java版本 "10.0.1" 2018-04-17
  # 我們需要匹配到行尾,以防止sed列印不匹配的字元。

  #此處匹配java的主版本號,jdk1.8之前的JAVA_MAJOR_VERSION都是1
  #jdk1.8往後就變成了9,10,11等
  JAVA_MAJOR_VERSION=$("$JAVA" -version 2>&1 | sed -E -n 's/.* version "([0-9]*).*$/\1/p')
  #如果JAVA_MAJOR_VERSION的版本號大於等於9話
  if [[ "$JAVA_MAJOR_VERSION" -ge "9" ]] ; then
    #設定KAFKA_GC_LOG_OPTS的值為 -Xlog:gc*:file=$LOG_DIR/$GC_LOG_FILE_NAME:time,tags:filecount=10,filesize=102400
    KAFKA_GC_LOG_OPTS="-Xlog:gc*:file=$LOG_DIR/$GC_LOG_FILE_NAME:time,tags:filecount=10,filesize=102400"
  else
    #否則設定為-Xloggc:$LOG_DIR/$GC_LOG_FILE_NAME -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintGCTimeStamps -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=10 -XX:GCLogFileSize=100M
    KAFKA_GC_LOG_OPTS="-Xloggc:$LOG_DIR/$GC_LOG_FILE_NAME -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintGCTimeStamps -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=10 -XX:GCLogFileSize=100M"
  fi
fi

# 從classpath中刪除可能的冒號字首(當CLASSPATH為空白時,發生在`CLASSPATH="$CLASSPATH:$file"`這樣的行)。
# 右側使用的語法是原生的Bash字串操作,更多細節請看下面的內容。
# http://tldp.org/LDP/abs/html/string-manipulation.html, 特別是標題為 "子串去除 "的部分。
#設定CLASSPATH的值為
CLASSPATH=${CLASSPATH#:}

#如果檢測到CGYWIN,需要把CLASSPATH的值轉化為windowns特有的格式
(( CYGWIN )) && CLASSPATH=$(cygpath --path --mixed "${CLASSPATH}")

#登入模式
#如果DAEMON_MODE是true的話
if [ "x$DAEMON_MODE" = "xtrue" ]; then
  #後臺執行程式,並列印到"$CONSOLE_OUTPUT_FILE" 檔案中
  nohup "$JAVA" $KAFKA_HEAP_OPTS $KAFKA_JVM_PERFORMANCE_OPTS $KAFKA_GC_LOG_OPTS $KAFKA_JMX_OPTS $KAFKA_LOG4J_OPTS -cp "$CLASSPATH" $KAFKA_OPTS "$@" > "$CONSOLE_OUTPUT_FILE" 2>&1 < /dev/null &
else
  #前臺之前,把日誌列印到前臺
  exec "$JAVA" $KAFKA_HEAP_OPTS $KAFKA_JVM_PERFORMANCE_OPTS $KAFKA_GC_LOG_OPTS $KAFKA_JMX_OPTS $KAFKA_LOG4J_OPTS -cp "$CLASSPATH" $KAFKA_OPTS "$@"
fi

  

 上面對指令碼進行了細緻的分析,但是最重要的其實我們要分析最後幾行程式碼,

我以bin/kafka-run-class.sh -name kafkaServer -loggc kafka.Kafka -deamon config/server.properties

為例子,最終經過這個kafka-run-class.sh指令碼後,最後其實真實執行的指令碼

nohup java -Xmx1G -Xms1G -server -XX:+UseG1GC -XX:MaxGCPauseMillis=20 -XX:InitiatingHeapOccupancyPercent=35 -XX:+ExplicitGCInvokesConcurrent -XX:MaxInlineLevel=15 
-Djava.awt.headless=true -Xloggc:/home/hadoop/software/kafka_2.13-2.5.1/bin/../logs/kafkaServer-gc.log 
-verbose:gc -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintGCTimeStamps -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=10 -XX:GCLogFileSize=100M 
-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.authenticate=false  -Dcom.sun.management.jmxremote.ssl=false  
-Dkafka.logs.dir=/home/hadoop/software/kafka_2.13-2.5.1/bin/../logs 
-Dlog4j.configuration=file:./../config/log4j.properties 
-cp /home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/activation-1.1.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/aopalliance-repackaged-2.5.0.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/argparse4j-0.7.0.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/audience-annotations-0.5.0.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/commons-cli-1.4.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/commons-lang3-3.8.1.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/connect-api-2.5.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/connect-basic-auth-extension-2.5.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/connect-file-2.5.1.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/connect-json-2.5.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/connect-mirror-2.5.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/connect-mirror-client-2.5.1.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/connect-runtime-2.5.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/connect-transforms-2.5.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/hk2-api-2.5.0.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/hk2-locator-2.5.0.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/hk2-utils-2.5.0.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jackson-annotations-2.10.2.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jackson-core-2.10.2.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jackson-databind-2.10.2.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jackson-dataformat-csv-2.10.2.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jackson-datatype-jdk8-2.10.2.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jackson-jaxrs-base-2.10.2.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jackson-jaxrs-json-provider-2.10.2.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jackson-module-jaxb-annotations-2.10.2.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jackson-module-paranamer-2.10.2.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jackson-module-scala_2.13-2.10.2.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jakarta.activation-api-1.2.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jakarta.annotation-api-1.3.4.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jakarta.inject-2.5.0.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jakarta.ws.rs-api-2.1.5.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jakarta.xml.bind-api-2.3.2.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/javassist-3.22.0-CR2.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/javassist-3.26.0-GA.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/javax.servlet-api-3.1.0.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/javax.ws.rs-api-2.1.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jaxb-api-2.3.0.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jersey-client-2.28.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jersey-common-2.28.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jersey-container-servlet-2.28.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jersey-container-servlet-core-2.28.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jersey-hk2-2.28.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jersey-media-jaxb-2.28.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jersey-server-2.28.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jetty-client-9.4.24.v20191120.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jetty-continuation-9.4.24.v20191120.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jetty-http-9.4.24.v20191120.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jetty-io-9.4.24.v20191120.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jetty-security-9.4.24.v20191120.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jetty-server-9.4.24.v20191120.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jetty-servlet-9.4.24.v20191120.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jetty-servlets-9.4.24.v20191120.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jetty-util-9.4.24.v20191120.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/jopt-simple-5.0.4.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/kafka_2.13-2.5.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/kafka_2.13-2.5.1-sources.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/kafka-clients-2.5.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/kafka-log4j-appender-2.5.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/kafka-streams-2.5.1.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/kafka-streams-examples-2.5.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/kafka-streams-scala_2.13-2.5.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/kafka-streams-test-utils-2.5.1.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/kafka-tools-2.5.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/log4j-1.2.17.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/lz4-java-1.7.1.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/maven-artifact-3.6.3.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/metrics-core-2.2.0.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/netty-buffer-4.1.50.Final.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/netty-codec-4.1.50.Final.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/netty-common-4.1.50.Final.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/netty-handler-4.1.50.Final.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/netty-resolver-4.1.50.Final.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/netty-transport-4.1.50.Final.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/netty-transport-native-epoll-4.1.50.Final.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/netty-transport-native-unix-common-4.1.50.Final.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/osgi-resource-locator-1.0.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/paranamer-2.8.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/plexus-utils-3.2.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/reflections-0.9.12.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/rocksdbjni-5.18.3.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/scala-collection-compat_2.13-2.1.3.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/scala-java8-compat_2.13-0.9.0.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/scala-library-2.13.1.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/scala-logging_2.13-3.9.2.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/scala-reflect-2.13.1.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/slf4j-api-1.7.30.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/slf4j-log4j12-1.7.30.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/snappy-java-1.1.7.3.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/validation-api-2.0.1.Final.jar:
/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/zookeeper-3.5.8.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/zookeeper-jute-3.5.8.jar:/home/hadoop/software/kafka_2.13-2.5.1/bin/../libs/zstd-jni-1.4.4-7.jar  
"kafka.Kafka ../conf/server.properties" > "/home/hadoop/software/kafka_2.13-2.5.1/bin/../logs/kafkaServer.out" 2>&1 < /dev/null &

 最終發現執行的是kafka.Kafka類,傳入的引數是 ../conf/server.properties,然後把日誌輸出到/home/hadoop/software/kafka_2.13-2.4.1/logs/kafkaServer.out檔案中。

後續的文章中我們將會繼續對kafka.Kafka的執行流程進行分析,本文先暫時分析shell指令碼部分。

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