ZooKeeper的日志和快照

ZooKeeper有两种日志、一种快照。日志分为事务日志和ZooKeeper运行时的系统日志。

1.事务日志和快照

ZooKeeper集群中的每个服务器节点每次接收到写操作请求时，都会先将这次请求发送给leader，leader将这次写操作转换为带有状态的事务，然后leader会对这次写操作广播出去以便进行协调。当协调通过(大多数节点允许这次写)后，leader通知所有的服务器节点，让它们将这次写操作应用到内存数据库中，并将其记录到事务日志中。

当事务日志记录的次数达到一定数量后(默认10W次)，就会将内存数据库序列化一次，使其持久化保存到磁盘上，序列化后的文件称为"快照文件"。每次拍快照都会生成新的事务日志。

有了事务日志和快照，就可以让任意节点恢复到任意时间点(只要没有清理事务日志和快照)。

1.1 事务日志和快照相关的配置项

• dataDir：
  ZooKeeper的数据目录，主要目的是存储内存数据库序列化后的快照路径。如果没有配置事务日志(即dataLogDir配置项)的路径，那么ZooKeeper的事务日志也存放在数据目录中。

• dataLogDir：
  指定事务日志的存放目录。事务日志对ZooKeeper的影响非常大，强烈建议事务日志目录和数据目录分开，不要将事务日志记录在数据目录(主要用来存放内存数据库快照)下。

• preAllocSize：
  为事务日志预先开辟磁盘空间。默认是64M，意味着每个事务日志大小就是64M(可以去事务日志目录中看一下，每个事务日志只要被创建出来，就是64M)。如果ZooKeeper产生快照频率较大，可以考虑减小这个参数，因为每次快照后都会切换到新的事务日志，但前面的64M根本就没写完。(见snapCount配置项)

• snapCount：
  ZooKeeper使用事务日志和快照来持久化每个事务(注意是日志先写)。该配置项指定ZooKeeper在将内存数据库序列化为快照之前，需要先写多少次事务日志。也就是说，每写几次事务日志，就快照一次。默认值为100000。为了防止所有的ZooKeeper服务器节点同时生成快照(一般情况下，所有实例的配置文件是完全相同的)，当某节点的先写事务数量在(snapCount/2+1,snapCount)范围内时(挑选一个随机值)，这个值就是该节点拍快照的时机。

• autopurge.snapRetainCount：
  该配置项指定开启了ZooKeeper的自动清理功能后(见下一个配置项)，每次自动清理时要保留的版本数量。默认值为3，最小值也为3。它表示在自动清理时，会保留最近3个快照以及这3个快照对应的事务日志。其它的所有快照和日志都清理。

• autopurge.purgeInterval：
  指定触发自动清理功能的时间间隔，单位为小时，值为大于或等于1的整数，默认值为0，表示不开启自动清理功能。

1.2 事务日志和快照的命名规则

在ZooKeeper集群启动后，当第一个客户端连接到某个服务器节点时，会创建一个会话，这个会话也是事务，于是创建第一个事务日志，一般名为log.100000001，这里的100000001是这次会话的事务id(zxid)。之后的事务都将写入到这个文件中，直到拍下一个快照。

如果是事务ZXID5触发的拍快照，那么快照名就是snapshot.ZXID5，拍完后，下一个事务的ID就是ZXID6，于是新的事务日志名为log.ZXID6。

1.3 查看事务日志

事务日志是一个二进制文件，无法直接查看。好在ZooKeeper提供了一个LogFormatter工具类。

假设ZooKeeper安装目录为/usr/local/zookeeper，那么可以通过下面的方法来查看事务日志log.100000001中的内容。

[root@node02 ~]# java -cp /usr/local/zookeeper/zookeeper-3.4.7.jar:/usr/local/zookeeper/lib/slf4j-api-1.6.1.jar org.apache.zookeeper.server.LogFormatter /usr/local/zookeeper/data/version-2/log.100000001
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
ZooKeeper Transactional Log File with dbid 0 txnlog format version 2
20-3-5 下午09时10分54秒 session 0x170aaceef8c0000 cxid 0x0 zxid 0x100000001 createSession 30000

20-3-5 下午09时10分54秒 session 0x170aaceef8c0000 cxid 0x1 zxid 0x100000002 create '/test_znode,#68656c6c6f20776f726c64,v{s{31,s{'world,'anyone}}},F,1

20-3-5 下午09时11分26秒 session 0x170aaceef8c0000 cxid 0x0 zxid 0x100000003 closeSession null
20-3-5 下午09时11分52秒 session 0x270aacedac50000 cxid 0x0 zxid 0x100000004 createSession 30000

20-3-5 下午09时12分22秒 session 0x270aacedac50001 cxid 0x0 zxid 0x100000005 createSession 30000

20-3-5 下午09时12分24秒 session 0x270aacedac50000 cxid 0x0 zxid 0x100000006 closeSession null
20-3-5 下午09时12分54秒 session 0x270aacedac50001 cxid 0x0 zxid 0x100000007 closeSession null
20-3-5 下午09时13分42秒 session 0x370aacef0570000 cxid 0x0 zxid 0x100000008 createSession 30000

20-3-5 下午09时14分14秒 session 0x370aacef0570000 cxid 0x0 zxid 0x100000009 closeSession null
20-3-5 下午09时16分55秒 session 0x170aaceef8c0001 cxid 0x0 zxid 0x10000000a createSession 30000

20-3-5 下午09时17分56秒 session 0x170aaceef8c0001 cxid 0x1 zxid 0x10000000b closeSession null
EOF reached after 11 txns.

1.4 自动清理功能

从ZooKeeper 3.4.0开始，ZooKeeper提供了自动清理事务日志和快照的功能，见事务日志和快照相关的配置项。

此外，还提供了一个脚本zkCleanup.sh，它也用来清理事务日志和快照。但比较少用。

有时也会写定时任务脚本，来删除定时、定点的事务日志和快照数据。

2.ZooKeeper系统的系统日志

ZooKeeper使用log4j(log for java)来记录系统日志。默认情况下，系统日志文件为ZooKeeper安装目录下的zookeeper.out，这是由log4j的配置文件决定的。(实际上，zkEnv.sh和zkServer.sh中也设置了日志的路径，见下文)。

ZooKeeper使用的log4j的配置文件为$ZOOKEEPER_HOME/conf/log4j.properties。

[root@node02 zookeeper]# cat conf/log4j.properties
# Define some default values that can be overridden by system properties
zookeeper.root.logger=INFO, CONSOLE
zookeeper.console.threshold=INFO
zookeeper.log.dir=.　　　　　　# 日志目录
zookeeper.log.file=zookeeper.log　　　　# 日志文件名称
zookeeper.log.threshold=DEBUG
zookeeper.tracelog.dir=.
zookeeper.tracelog.file=zookeeper_trace.log

#
# ZooKeeper Logging Configuration
#

# Format is "<default threshold> (, <appender>)+

# DEFAULT: console appender only
log4j.rootLogger=${zookeeper.root.logger}

# Example with rolling log file
#log4j.rootLogger=DEBUG, CONSOLE, ROLLINGFILE

# Example with rolling log file and tracing
#log4j.rootLogger=TRACE, CONSOLE, ROLLINGFILE, TRACEFILE

#
# Log INFO level and above messages to the console
#
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.Threshold=${zookeeper.console.threshold}
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n

#
# Add ROLLINGFILE to rootLogger to get log file output
#    Log DEBUG level and above messages to a log file
log4j.appender.ROLLINGFILE=org.apache.log4j.RollingFileAppender
log4j.appender.ROLLINGFILE.Threshold=${zookeeper.log.threshold}
log4j.appender.ROLLINGFILE.File=${zookeeper.log.dir}/${zookeeper.log.file}

# Max log file size of 10MB
log4j.appender.ROLLINGFILE.MaxFileSize=10MB
# uncomment the next line to limit number of backup files
#log4j.appender.ROLLINGFILE.MaxBackupIndex=10

log4j.appender.ROLLINGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.ROLLINGFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n


#
# Add TRACEFILE to rootLogger to get log file output
#    Log DEBUG level and above messages to a log file
log4j.appender.TRACEFILE=org.apache.log4j.FileAppender
log4j.appender.TRACEFILE.Threshold=TRACE
log4j.appender.TRACEFILE.File=${zookeeper.tracelog.dir}/${zookeeper.tracelog.file}

log4j.appender.TRACEFILE.layout=org.apache.log4j.PatternLayout
### Notice we are including log4j's NDC here (%x)
log4j.appender.TRACEFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L][%x] - %m%n

log4j.properties中没有指定zookeeper.out啊？但为什么会输出到zookeeper.out中呢？这是因为zkServer.sh中指定了这个文件。以下是zkServer.sh中和zookeeper.out相关的内容：

[root@node02 conf]# cat /usr/local/zookeeper/bin/zkServer.sh
#!/usr/bin/env 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.

#
# If this scripted is run out of /usr/bin or some other system bin directory
# it should be linked to and not copied. Things like java jar files are found
# relative to the canonical path of this script.
#



# use POSTIX interface, symlink is followed automatically
ZOOBIN="${BASH_SOURCE-$0}"
ZOOBIN="$(dirname "${ZOOBIN}")"
ZOOBINDIR="$(cd "${ZOOBIN}"; pwd)"

if [ -e "$ZOOBIN/../libexec/zkEnv.sh" ]; then
  . "$ZOOBINDIR/../libexec/zkEnv.sh"
else
  . "$ZOOBINDIR/zkEnv.sh"
fi

# See the following page for extensive details on setting
# up the JVM to accept JMX remote management:
# http://java.sun.com/javase/6/docs/technotes/guides/management/agent.html
# by default we allow local JMX connections
if [ "x$JMXLOCALONLY" = "x" ]
then
    JMXLOCALONLY=false
fi

if [ "x$JMXDISABLE" = "x" ]
then
  echo "ZooKeeper JMX enabled by default" >&2
  if [ "x$JMXPORT" = "x" ]
  then
    # for some reason these two options are necessary on jdk6 on Ubuntu
    #   accord to the docs they are not necessary, but otw jconsole cannot
    #   do a local attach
    ZOOMAIN="-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.local.only=$JMXLOCALONLY org.apache.zookeeper.server.quorum.QuorumPeerMain"
  else
    if [ "x$JMXAUTH" = "x" ]
    then
      JMXAUTH=false
    fi
    if [ "x$JMXSSL" = "x" ]
    then
      JMXSSL=false
    fi
    if [ "x$JMXLOG4J" = "x" ]
    then
      JMXLOG4J=true
    fi
    echo "ZooKeeper remote JMX Port set to $JMXPORT" >&2
    echo "ZooKeeper remote JMX authenticate set to $JMXAUTH" >&2
    echo "ZooKeeper remote JMX ssl set to $JMXSSL" >&2
    echo "ZooKeeper remote JMX log4j set to $JMXLOG4J" >&2
    ZOOMAIN="-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=$JMXPORT -Dcom.sun.management.jmxremote.authenticate=$JMXAUTH -Dcom.sun.management.jmxremote.ssl=$JMXSSL -Dzookeeper.jmx.log4j.disable=$JMXLOG4J org.apache.zookeeper.server.quorum.QuorumPeerMain"
  fi
else
    echo "JMX disabled by user request" >&2
    ZOOMAIN="org.apache.zookeeper.server.quorum.QuorumPeerMain"
fi

if [ "x$SERVER_JVMFLAGS"  != "x" ]
then
    JVMFLAGS="$SERVER_JVMFLAGS $JVMFLAGS"
fi

if [ "x$2" != "x" ]
then
    ZOOCFG="$ZOOCFGDIR/$2"
fi

# if we give a more complicated path to the config, don't screw around in $ZOOCFGDIR
if [ "x$(dirname "$ZOOCFG")" != "x$ZOOCFGDIR" ]
then
    ZOOCFG="$2"
fi

if $cygwin
then
    ZOOCFG=`cygpath -wp "$ZOOCFG"`
    # cygwin has a "kill" in the shell itself, gets confused
    KILL=/bin/kill
else
    KILL=kill
fi

echo "Using config: $ZOOCFG" >&2

case "$OSTYPE" in
*solaris*)
  GREP=/usr/xpg4/bin/grep
  ;;
*)
  GREP=grep
  ;;
esac
if [ -z "$ZOOPIDFILE" ]; then
    ZOO_DATADIR="$($GREP "^[[:space:]]*dataDir" "$ZOOCFG" | sed -e 's/.*=//')"
    if [ ! -d "$ZOO_DATADIR" ]; then
        mkdir -p "$ZOO_DATADIR"
    fi
    ZOOPIDFILE="$ZOO_DATADIR/zookeeper_server.pid"
else
    # ensure it exists, otw stop will fail
    mkdir -p "$(dirname "$ZOOPIDFILE")"
fi

if [ ! -w "$ZOO_LOG_DIR" ] ; then
mkdir -p "$ZOO_LOG_DIR"
fi

_ZOO_DAEMON_OUT="$ZOO_LOG_DIR/zookeeper.out"

case $1 in
start)
    echo  -n "Starting zookeeper ... "
    if [ -f "$ZOOPIDFILE" ]; then
      if kill -0 `cat "$ZOOPIDFILE"` > /dev/null 2>&1; then
         echo $command already running as process `cat "$ZOOPIDFILE"`. 
         exit 0
      fi
    fi
    nohup "$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" \
    -cp "$CLASSPATH" $JVMFLAGS $ZOOMAIN "$ZOOCFG" > "$_ZOO_DAEMON_OUT" 2>&1 < /dev/null &
    if [ $? -eq 0 ]
    then
      case "$OSTYPE" in
      *solaris*)
        /bin/echo "${!}\\c" > "$ZOOPIDFILE"
        ;;
      *)
        /bin/echo -n $! > "$ZOOPIDFILE"
        ;;
      esac
      if [ $? -eq 0 ];
      then
        sleep 1
        echo STARTED
      else
        echo FAILED TO WRITE PID
        exit 1
      fi
    else
      echo SERVER DID NOT START
      exit 1
    fi
    ;;
start-foreground)
    ZOO_CMD=(exec "$JAVA")
    if [ "${ZOO_NOEXEC}" != "" ]; then
      ZOO_CMD=("$JAVA")
    fi
    "${ZOO_CMD[@]}" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" \
    -cp "$CLASSPATH" $JVMFLAGS $ZOOMAIN "$ZOOCFG"
    ;;
print-cmd)
    echo "\"$JAVA\" -Dzookeeper.log.dir=\"${ZOO_LOG_DIR}\" -Dzookeeper.root.logger=\"${ZOO_LOG4J_PROP}\" -cp \"$CLASSPATH\" $JVMFLAGS $ZOOMAIN \"$ZOOCFG\" > \"$_ZOO_DAEMON_OUT\" 2>&1 < /dev/null"
    ;;
stop)
    echo -n "Stopping zookeeper ... "
    if [ ! -f "$ZOOPIDFILE" ]
    then
      echo "no zookeeper to stop (could not find file $ZOOPIDFILE)"
    else
      $KILL -9 $(cat "$ZOOPIDFILE")
      rm "$ZOOPIDFILE"
      echo STOPPED
    fi
    exit 0
    ;;
upgrade)
    shift
    echo "upgrading the servers to 3.*"
    "$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" \
    -cp "$CLASSPATH" $JVMFLAGS org.apache.zookeeper.server.upgrade.UpgradeMain ${@}
    echo "Upgrading ... "
    ;;
restart)
    shift
    "$0" stop ${@}
    sleep 3
    "$0" start ${@}
    ;;
status)
    # -q is necessary on some versions of linux where nc returns too quickly, and no stat result is output
    clientPortAddress=`$GREP "^[[:space:]]*clientPortAddress[^[:alpha:]]" "$ZOOCFG" | sed -e 's/.*=//'`
    if ! [ $clientPortAddress ]
    then
        clientPortAddress="localhost"
    fi
    clientPort=`$GREP "^[[:space:]]*clientPort[^[:alpha:]]" "$ZOOCFG" | sed -e 's/.*=//'`
    STAT=`"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" \
             -cp "$CLASSPATH" $JVMFLAGS org.apache.zookeeper.client.FourLetterWordMain \
             $clientPortAddress $clientPort srvr 2> /dev/null    \
          | $GREP Mode`
    if [ "x$STAT" = "x" ]
    then
        echo "Error contacting service. It is probably not running."
        exit 1
    else
        echo $STAT
        exit 0
    fi
    ;;
*)
    echo "Usage: $0 {start|start-foreground|stop|restart|status|upgrade|print-cmd}" >&2

esac
[root@node02 conf]# 

可以看到，在zkServer.sh的start选项中，使用nohup启动ZooKeeper，并将日志输出到"$ZOO_LOG_DIR/zookeeper.out"中。

一般来说，没有特殊需求，没必要去改log4j日志配置。要改的话，记得把log4j.properties和zkEnv.sh和zkServer.sh中相关的内容都修改掉。