[
https://issues.apache.org/jira/browse/HADOOP-1134?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12500758
]
Doug Cutting commented on HADOOP-1134:
--------------------------------------
> I am still not clear which length is missing.
It's a minor point, but if we write async-io daemons for this protocol then the
easier it is to parse the total packet length the easier it will be to write
these daemons. So placing the total packet length in a fixed position at the
front of the packet so that it may be generically accessed without having to
determine what kind of a packet it is, will simplify things. An async daemon
will typically buffer entire requests as they arrive in small bits, then, once
a request is complete, perform an action. However we can always add such a
length on later, if and when we write async daemons, but it may then take
longer to roll out such daemons, as it may require protocol changes.
> So start_offset can be removed from DATA_CHUNK. I would prefer to keep the
> length so that loops that read and write to these streams could be a little
> simpler.
That sounds fine.
> only notable code replication I see is retry logic in
> FSInputChecker.readBuffer() where SeekToNewSource() and reportChecksumFailure
> are executed
Which is some of the most delicate code, that has taken several revisions to
get to its current level of correctness. In other words, logic that shouldn't
be replicated if at all possible.
> Block level CRCs in HDFS
> ------------------------
>
> Key: HADOOP-1134
> URL: https://issues.apache.org/jira/browse/HADOOP-1134
> Project: Hadoop
> Issue Type: New Feature
> Components: dfs
> Reporter: Raghu Angadi
> Assignee: Raghu Angadi
> Attachments: bc-no-upgrade-05302007.patch,
> DfsBlockCrcDesign-05305007.htm
>
>
> Currently CRCs are handled at FileSystem level and are transparent to core
> HDFS. See recent improvement HADOOP-928 ( that can add checksums to a given
> filesystem ) regd more about it. Though this served us well there a few
> disadvantages :
> 1) This doubles namespace in HDFS ( or other filesystem implementations ). In
> many cases, it nearly doubles the number of blocks. Taking namenode out of
> CRCs would nearly double namespace performance both in terms of CPU and
> memory.
> 2) Since CRCs are transparent to HDFS, it can not actively detect corrupted
> blocks. With block level CRCs, Datanode can periodically verify the checksums
> and report corruptions to namnode such that name replicas can be created.
> We propose to have CRCs maintained for all HDFS data in much the same way as
> in GFS. I will update the jira with detailed requirements and design. This
> will include same guarantees provided by current implementation and will
> include a upgrade of current data.
>
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
