7
我遇到了一個奇怪的問題。當我運行在一個大的數據集我的Hadoop作業（> 1TB壓縮文本文件），數的減少任務失敗，有這樣的蹤跡：Hadoop：中間合併失敗
java.io.IOException: Task: attempt_201104061411_0002_r_000044_0 - The reduce copier failed
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:385)
at org.apache.hadoop.mapred.Child$4.run(Child.java:240)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1115)
at org.apache.hadoop.mapred.Child.main(Child.java:234)
Caused by: java.io.IOException: Intermediate merge failed
at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$InMemFSMergeThread.doInMemMerge(ReduceTask.java:2714)
at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$InMemFSMergeThread.run(ReduceTask.java:2639)
Caused by: java.lang.RuntimeException: java.io.EOFException
at org.apache.hadoop.io.WritableComparator.compare(WritableComparator.java:128)
at org.apache.hadoop.mapred.Merger$MergeQueue.lessThan(Merger.java:373)
at org.apache.hadoop.util.PriorityQueue.downHeap(PriorityQueue.java:139)
at org.apache.hadoop.util.PriorityQueue.adjustTop(PriorityQueue.java:103)
at org.apache.hadoop.mapred.Merger$MergeQueue.adjustPriorityQueue(Merger.java:335)
at org.apache.hadoop.mapred.Merger$MergeQueue.next(Merger.java:350)
at org.apache.hadoop.mapred.Merger.writeFile(Merger.java:156)
at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$InMemFSMergeThread.doInMemMerge(ReduceTask.java:2698)
... 1 more
Caused by: java.io.EOFException
at java.io.DataInputStream.readInt(DataInputStream.java:375)
at com.__.hadoop.pixel.segments.IpCookieCountFilter$IpAndIpCookieCount.readFields(IpCookieCountFilter.java:241)
at org.apache.hadoop.io.WritableComparator.compare(WritableComparator.java:125)
... 8 more
java.io.IOException: Task: attempt_201104061411_0002_r_000056_0 - The reduce copier failed
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:385)
at org.apache.hadoop.mapred.Child$4.run(Child.java:240)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1115)
at org.apache.hadoop.mapred.Child.main(Child.java:234)
Caused by: java.io.IOException: Intermediate merge failed
at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$InMemFSMergeThread.doInMemMerge(ReduceTask.java:2714)
at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$InMemFSMergeThread.run(ReduceTask.java:2639)
Caused by: java.lang.RuntimeException: java.io.EOFException
at org.apache.hadoop.io.WritableComparator.compare(WritableComparator.java:128)
at org.apache.hadoop.mapred.Merger$MergeQueue.lessThan(Merger.java:373)
at org.apache.hadoop.util.PriorityQueue.upHeap(PriorityQueue.java:123)
at org.apache.hadoop.util.PriorityQueue.put(PriorityQueue.java:50)
at org.apache.hadoop.mapred.Merger$MergeQueue.merge(Merger.java:447)
at org.apache.hadoop.mapred.Merger$MergeQueue.merge(Merger.java:381)
at org.apache.hadoop.mapred.Merger.merge(Merger.java:107)
at org.apache.hadoop.mapred.Merger.merge(Merger.java:93)
at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$InMemFSMergeThread.doInMemMerge(ReduceTask.java:2689)
... 1 more
Caused by: java.io.EOFException
at java.io.DataInputStream.readFully(DataInputStream.java:180)
at org.apache.hadoop.io.Text.readString(Text.java:402)
at com.__.hadoop.pixel.segments.IpCookieCountFilter$IpAndIpCookieCount.readFields(IpCookieCountFilter.java:240)
at org.apache.hadoop.io.WritableComparator.compare(WritableComparator.java:122)
... 9 more
不是我一個人的減速器失敗。在我看到別人失敗之前，有幾個人往往成功。正如你所看到的，堆棧跟蹤始終似乎始於IPAndIPCookieCount.readFields()，並且始終處於內存合併階段，但並不總是來自readFields的相同部分。
當在較小的數據集上運行（約爲大小的1/30）時，此作業成功。作業的輸入量幾乎與輸出量一樣多，但每個輸出記錄都較短。這項工作本質上是第二類的實施。
我們正在使用CDH3 Hadoop發行版。
這裏是我的自定義WritableComparable實現：
public static class IpAndIpCookieCount implements WritableComparable<IpAndIpCookieCount> {
private String ip;
private int ipCookieCount;
public IpAndIpCookieCount() {
// empty constructor for hadoop
}
public IpAndIpCookieCount(String ip, int ipCookieCount) {
this.ip = ip;
this.ipCookieCount = ipCookieCount;
}
public String getIp() {
return ip;
}
public int getIpCookieCount() {
return ipCookieCount;
}
@Override
public void readFields(DataInput in) throws IOException {
ip = Text.readString(in);
ipCookieCount = in.readInt();
}
@Override
public void write(DataOutput out) throws IOException {
Text.writeString(out, ip);
out.writeInt(ipCookieCount);
}
@Override
public int compareTo(IpAndIpCookieCount other) {
int firstComparison = ip.compareTo(other.getIp());
if (firstComparison == 0) {
int otherIpCookieCount = other.getIpCookieCount();
if (ipCookieCount == otherIpCookieCount) {
return 0;
} else {
return ipCookieCount < otherIpCookieCount ? 1 : -1;
}
} else {
return firstComparison;
}
}
@Override
public boolean equals(Object o) {
if (o instanceof IpAndIpCookieCount) {
IpAndIpCookieCount other = (IpAndIpCookieCount) o;
return ip.equals(other.getIp()) && ipCookieCount == other.getIpCookieCount();
} else {
return false;
}
}
@Override
public int hashCode() {
return ip.hashCode()^ipCookieCount;
}
}
的readFields方法很簡單，我看不出在這個類的任何問題。另外，我看到其他人基本上得到同樣的堆棧跟蹤：
- http://lucene.472066.n3.nabble.com/Reduce-Copier-Failed-td2120228.html
- https://groups.google.com/a/cloudera.org/group/cdh-user/browse_thread/thread/3544da912bf66506
- http://www.listware.net/201010/hadoop-common-user/70382-merging-of-the-local-fs-files-threw-an-exception-javaioioexception-javalangruntimeexception-javaioeofexception.html
- http://mail-archives.apache.org/mod_mbox/hadoop-mapreduce-user/201101.mbox/%[email protected]%3E
- http://web.archiveorange.com/archive/v/5nvvZTgeqwCRQ3F9vEzI
無似乎已經真正想通了這背後的問題。最後兩個似乎表明這可能是一個內存問題（儘管這些堆棧跟蹤不是OutOfMemoryException）。就像鏈接列表中倒數第二個帖子一樣，我試圖設置更高的縮減器數量（最多999），但我仍然失敗。我還沒有嘗試分配更多內存來減少任務，因爲這需要我們重新配置集羣。
這是Hadoop中的錯誤嗎？或者我做錯了什麼？
編輯：我的數據按天劃分。如果我運行7次，每天運行一次，全部7次完成。如果我在7天內完成一項工作，則失敗。整個7天的大報告將看到完全相同的密鑰，與較小的一樣（總計），但顯然不是相同的順序，在相同的減速器等。
我也遇到過這個問題，但它並不是一直出現的。在相同的數據集上，運行在相同的條件下，有時我的作業會失敗，並且'WritableComparable.readFields（..）'方法中的'readByte（）'方法導致'EOFException'。我認爲這可能是導致某種延遲的網絡問題。 – 2012-08-15 09:52:30