[ https://issues.apache.org/jira/browse/HDFS-767?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Ning Zhang updated HDFS-767: ---------------------------- Attachment: HDFS-767.patch HDFS-767.patch contains the following changes: 1) code change in DFSClient.java to add random backoff discussed in this JIRA. 2) add unit test in TestDFSClientRetries to test effectiveness and performance of different parameters settings. > Job failure due to BlockMissingException > ---------------------------------------- > > Key: HDFS-767 > URL: https://issues.apache.org/jira/browse/HDFS-767 > Project: Hadoop HDFS > Issue Type: Improvement > Reporter: Ning Zhang > Attachments: HDFS-767.patch > > > If a block is request by too many mappers/reducers (say, 3000) at the same > time, a BlockMissingException is thrown because it exceeds the upper limit (I > think 256 by default) of number of threads accessing the same block at the > same time. The DFSClient wil catch that exception and retry 3 times after > waiting for 3 seconds. Since the wait time is a fixed value, a lot of clients > will retry at about the same time and a large portion of them get another > failure. After 3 retries, there are about 256*4 = 1024 clients got the block. > If the number of clients are more than that, the job will fail. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.