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實作四： Hadoop 叢集進階用法
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= 狀況一： 如何動態加入datanode 與 tasktracker =
* 某些情況下，後來的環境也許會跟之前配置的不同，比如說，原本只有五台機器架設hadoop，但是也許老闆今天心血來潮，又撥了五台電腦給你。在接續之前的環境動態的擴增節點的方法，請看以下作法。
== 1.0 說明 ==
* 要新增的節點上，hadoop版本與設定檔要與原先的相同
* 是否能連到正確的位址取決於conf/hadoop-site.xml內的jobTracker, Namenode資訊是否正確 (目前測試結果與conf/slave、masters無關)
== 1.1 加入datanode ==
* 在要加入的節點上面下此指令
{{{
$ cd $HADOOP_HOME
$ bin/hadoop-daemon.sh --config ./conf start datanode
}}}
* 執行畫面如下：
{{{
starting datanode, logging to /tmp/hadoop/logs/hadoop-waue-datanode-Dx7200.out
}}}
== 1.2 加入 taskTracker ==
* 是否能連到正確的namenode取決於conf/hadoop-site.xml，目前測試結果與conf/slave、masters無關
{{{
$ cd $HADOOP_HOME
$ bin/hadoop-daemon.sh --config ./conf start tasktracker
}}}
* 執行畫面如下：
{{{
starting tasktracker, logging to /tmp/hadoop/logs/hadoop-waue-tasktracker-Dx7200.out
}}}
-----
= 狀況二： 怎麼讓我的HDFS內資料均勻分散於各個Node上 =
* 下面指令用於分析數據塊分佈和重新平衡!DataNode上的數據分佈
{{{
$ bin/hadoop balancer
}}}
* 執行畫面如下
{{{
Time Stamp Iteration# Bytes Already Moved Bytes Left To Move Bytes Being Moved
09/04/01 18:00:08 INFO net.NetworkTopology: Adding a new node: /default-rack/140.110.138.191:50010
09/04/01 18:00:08 INFO net.NetworkTopology: Adding a new node: /default-rack/140.110.141.129:50010
09/04/01 18:00:08 INFO dfs.Balancer: 0 over utilized nodes:
09/04/01 18:00:08 INFO dfs.Balancer: 0 under utilized nodes:
The cluster is balanced. Exiting...
Balancing took 186.0 milliseconds
}}}
------
= 狀況三：如何讓已上線服務的Hadoop進行升級並且不失去以前的資料 =
* 假設從原本的hadoop 0.16升級到hadoop 0.18
* 如果把conf/這個資料夾至於$Hadoop_home目錄下的話，一旦換版本就連conf也被一併換掉，但無論hadoop的版本新舊，其實設定檔及其資訊是可以共用的。
== step 1. 停止hdfs ==
* 先看狀態
{{{
$ cd /opt/hadoop/
$ bin/hadoop dfsadmin -upgradeProgress status
There are no upgrades in progress.
}}}
* 停止hdfs
* 注意不可使用bin/stop-all.sh來停止
{{{
$ bin/stop-dfs.sh
}}}
== Step 2. 鍊結新版本hadoop ==
* 把conf 移至/opt/conf ，hadoop 0.16 與 hadoop 0.18用 ln 做捷徑代換。
* 以下假設你已經下載好hadoop0.18並解壓縮後，資料夾名稱為hadoop-0.18.3
{{{
$ cd opt/
$ mv hadoop/conf ./
$ mv hadoop hadoop-0.16
$ ln hadoop-0.18.3 hadoop
}}}
== step 3. 設置環境變數 ==
* 由於conf已不在hadoop_home內，因此記得匯入conf/hadoop-env.sh的參數
* 填入hadoop-env.sh 內$HADOOP_CONF_DIR正確路徑，並匯入資訊
{{{
$ source /opt/conf/hadoop-env.sh
}}}
== step 4. 每個節點都部署新版本的Hadoop ==
* 若有多個node的話，則每個node的hadoop版本都要統一，否則會出現問題
== step 5. 啟動 ==
{{{
$ bin/start-dfs.sh -upgrade
}}}
* namenode管理網頁會出現升級狀態
-------
= 狀況四：如何讓已上線服務的Hadoop進行降級並且不失去以前的資料 =
* 此情況與狀況三相反，因此作法類似狀況三，下面的狀況假設設定檔已在/opt/conf內，並且/opt內也都有hadoop-0.16 與 hadoop-0.18.3 兩個資料夾，而且節點只有一台。
== step 1. 停止 HDFS ==
{{{
$ cd /opt/hadoop
$ bin/stop-dfs.sh
}}}
== step 2. 部署老版本的Hadoop ==
{{{
$ rm /opt/hadoop
$ ln hadoop-0.16 hadoop
}}}
== step 3. 退回之前版本 ==
{{{
$ bin/start-dfs.sh -rollback
}}}
-----
= 狀況五：我的HDFS檔案系統是否正常 =
* 在此介紹HDFS文件系統檢查工具 "bin/hadoop fsck"
{{{
$ bin/hadoop fsck /
}}}
* 執行畫面如下
{{{
.
/user/waue/input/1.txt: Under replicated blk_-90085106852013388_1001. Target Replicas is 3 but found 2 replica(s).
/user/waue/input/1.txt: Under replicated blk_-4027196261436469955_1001. Target Replicas is 3 but found 2 replica(s).
.
/user/waue/input/2.txt: Under replicated blk_-2300843106107816641_1002. Target Replicas is 3 but found 2 replica(s).
.
/user/waue/input/3.txt: Under replicated blk_-1561577350198661966_1003. Target Replicas is 3 but found 2 replica(s).
.
/user/waue/input/4.txt: Under replicated blk_1316726598778579026_1004. Target Replicas is 3 but found 2 replica(s).
Status: HEALTHY
Total size: 143451003 B
Total dirs: 8
Total files: 4
Total blocks (validated): 5 (avg. block size 28690200 B)
Minimally replicated blocks: 5 (100.0 %)
Over-replicated blocks: 0 (0.0 %)
Under-replicated blocks: 5 (100.0 %)
Mis-replicated blocks: 0 (0.0 %)
Default replication factor: 3
Average block replication: 2.0
Corrupt blocks: 0
Missing replicas: 5 (50.0 %)
Number of data-nodes: 2
Number of racks: 1
The filesystem under path '/' is HEALTHY
}}}
* 加不同的參數有不同的用處，如
{{{
$ bin/hadoop fsck / -files
}}}
* 執行畫面如下
{{{
/tmp
/tmp/hadoop
/tmp/hadoop/hadoop-waue
/tmp/hadoop/hadoop-waue/mapred
/tmp/hadoop/hadoop-waue/mapred/system
/user
/user/waue
/user/waue/input
/user/waue/input/1.txt 115045564 bytes, 2 block(s): Under replicated blk_-90085106852013388_1001. Target Replicas is 3 but found 2 replica(s).
Under replicated blk_-4027196261436469955_1001. Target Replicas is 3 but found 2 replica(s).
/user/waue/input/2.txt 987864 bytes, 1 block(s): Under replicated blk_-2300843106107816641_1002. Target Replicas is 3 but found 2 replica(s).
/user/waue/input/3.txt 1573048 bytes, 1 block(s): Under replicated blk_-1561577350198661966_1003. Target Replicas is 3 but found 2 replica(s).
/user/waue/input/4.txt 25844527 bytes, 1 block(s): Under replicated blk_1316726598778579026_1004. Target Replicas is 3 but found 2 replica(s).
Status: HEALTHY
....（同上）
}}}
-----
= 狀況六：我的系統似乎跑太多Job，我要幫他減肥 =
== step 1. 把所有程序列出來 ==
* 可到JobTracker:50030網頁來看程序的Jobid
* 或用指令印出所有程序
{{{
$ bin/hadoop job -list all
5 jobs submitted
States are:
Running : 1 Succeded : 2 Failed : 3 Prep : 4
JobId State StartTime UserName
job_200904021140_0001 2 1238652150499 waue
job_200904021140_0002 3 1238657754096 waue
job_200904021140_0004 3 1238657989495 waue
job_200904021140_0005 2 1238658076347 waue
job_200904021140_0006 2 1238658644666 waue
}}}
== step 2. more detail ==
* 查看工作狀態
{{{
$ bin/hadoop job -status job_200904021140_0001
}}}
* 印出程序的歷史狀態
{{{
$ bin/hadoop job -history /user/waue/stream-output1
Hadoop job: job_200904021140_0005
=====================================
Job tracker host name: gm1.nchc.org.tw
job tracker start time: Thu Apr 02 11:40:06 CST 2009
User: waue
JobName: streamjob9019.jar
JobConf: hdfs://gm1.nchc.org.tw:9000/tmp/hadoop/hadoop-waue/mapred/system/job_200904021140_0005/job.xml
Submitted At: 2-四月-2009 15:41:16
Launched At: 2-四月-2009 15:41:16 (0sec)
Finished At: 2-四月-2009 15:42:04 (48sec)
Status: SUCCESS
=====================================
...略
}}}
== step 3. 殺很大、殺不用錢 ==
* 終止正在執行的程序，如 id 為 job_200904021140_0001
{{{
$ bin/hadoop job -kill job_200904021140_0001
}}}
--------
= 狀況七：怎麼看目前的Hadoop版本 =
* 印出目前的hadoop 版本
{{{
$ bin/hadoop version
}}}
* 執行畫面
{{{
Hadoop 0.18.3
Subversion https://svn.apache.org/repos/asf/hadoop/core/branches/branch-0.18 -r 736250
Compiled by ndaley on Thu Jan 22 23:12:08 UTC 2009
}}}
-----
= 狀況八：我要設定HDFS的帳戶及配額 =
== step 1. 先設定各使用者的預設資料夾，屬性及讀寫權限 ==
* hdfs的權限有owner, group, other三種
* 而用戶的身份取決於client上的使用者 （用 whoami），群組為（bash -c groups）
* 相關的操作：
{{{
$ bin/hadoop dfs -mkdir own
$ bin/hadoop dfs -chmod -R 755 own
$ bin/hadoop dfs -chgrp -R waue own
$ bin/hadoop dfs -chown -R waue own
$ bin/hadoop dfs -lsr own
}}}
* conf/hadoop-site.xml 可用參數：
{{{
#!php
dfs.permissions = true
dfs.web.ugi = webuser,webgroup
dfs.permissions.supergroup = supergroup
dfs.upgrade.permission = 777
dfs.umask = 022
}}}
== step 2. 設定配額 ==
* 目錄配額是對目錄樹上該目錄下的名字數量做硬性限制
* 設定配額，數字代表個數 （如：我上傳了一個2個block的檔案可以上傳，但我上傳兩個檔案很小的檔上去卻不行）
* 配額為1可以強制目錄保持為空
* 重命名不會改變該目錄的配額
{{{
$ bin/hadoop dfs -mkdir quota
$ bin/hadoop dfsadmin -setQuota 2 quota
$ bin/hadoop dfs -put ../conf/hadoop-env.sh quota/
$ bin/hadoop dfs -put ../conf/hadoop-site.xml quota/
put: org.apache.hadoop.dfs.QuotaExceededException: The quota of /user/waue/quota is exceeded: quota=2 count=3
}}}
* 檢查目錄的配額方法： "bin/hadoop fs -count -q <目錄> "
{{{
$ bin/hadoop fs -count -q own
none inf 1 0 0 hdfs://gm1.nchc.org.tw:9000/user/waue/own
$ bin/hadoop dfsadmin -setQuota 4 own
$ bin/hadoop fs -count -q own
4 3 1 0 0 hdfs://gm1.nchc.org.tw:9000/user/waue/own
}}}
* 清除之前設定的配額
{{{
$ bin/hadoop dfsadmin -clrQuota quota/
}}}