hadoop-hdfs-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Walter Su (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-8881) Erasure Coding: internal blocks got missed and got over-replicated at the same time
Date Sat, 08 Aug 2015 07:11:45 GMT
Walter Su created HDFS-8881:
-------------------------------

             Summary: Erasure Coding: internal blocks got missed and got over-replicated at
the same time
                 Key: HDFS-8881
                 URL: https://issues.apache.org/jira/browse/HDFS-8881
             Project: Hadoop HDFS
          Issue Type: Sub-task
            Reporter: Walter Su
            Assignee: Walter Su


We know the Repl checking depends on {{BlockManager#countNodes()}}, but countNodes() has limitation
for striped blockGroup.

*One* missing internal block will be catched by Repl checking, and handled by ReplicationMonitor.
*One* over-replicated internal block will be catched by Repl checking, and handled by processOverReplicatedBlocks.
*One* missing internal block and *two* over-replicated internal blocks *at the same time*
will be catched by Repl checking, and handled by processOverReplicatedBlocks, later by ReplicationMonitor.
*One* missing internal block and *One* over-replicated internal block *at the same time* will
*NOT* be catched by Repl checking.

"at the same time" means one missing internal block can't be recovered, and one internal block
got over-replicated anyway. For example:

scenario A:
step 1. block #0 and #1 are reported missing.
2. a new #1 got recovered.
3. the old #1 come back, and the recovery work for #0 failed.

scenario B:
1. An DN decommissioned/dead which has #1.
2. block #0 is reported missing.
3. The DN has #1 recommisioned, and the recovery work for #0 failed.

In the end, the blockGroup has \[1, 1, 2, 3, 4, 5, 6, 7, 8\], assume 6+3 schema. Client always
needs to decode #0 if the blockGroup doesn't get handled.



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)

Mime
View raw message