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From "Weiwei Yang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-12283) Ozone: DeleteKey-5: Implement SCM DeletedBlockLog
Date Mon, 14 Aug 2017 15:30:01 GMT

    [ https://issues.apache.org/jira/browse/HDFS-12283?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16125837#comment-16125837

Weiwei Yang commented on HDFS-12283:

Hi [~yuanbo]

Thanks for working on this and posting a patch, we are made good progress here. Despite the
findbugs and checkstyle issues, I have some more comments


Can we move the protobuf definition code here to {{StorageContainerDatanodeProtocol.proto}}?
Since this proto is serving the protocol between SCM and datanode.


line 25 - 30, suggestion to add some more explaination to the java doc, such as: a block deletion
transaction represents a block deletion message send from SCM to datanode, which contains
a number of under deletion blocks in a container and a txid as an unique ID to track the progress.


minor line 53: suggest to remove word DB from the java doc, as the interface might be implemented
by some other form of logs in future


line 56: I think the log impl should be self contained, we don't need to pass a {{MetadataStore}}
argument in its constructor.  The constructor should handle following cases, 1) if db already
exists, load the db using metadata store API; 2) if db doesn't exists, create the DB on the
given path (from configuration); 

line 70: this iterates the DB to get latest key, this is not efficiency I think. Maybe we
can maintain latest txid in same database with a prefix? e.g #latest#latest_txid

line 110: this might have problem.. e.g you have listed tx 1,3,5 (2,4 has been committed),
then 4 won't be a valid start key anymore.

line 141: should it be {{> MAX_RETRY}}? The init count is 0, means this transaction has
not yet sent to datanode, if we want to support max time of retries, e.g 5, we need to revise
this check to >5, correct?

line 189: this may introduce some race condition here. For example, if line 189 succeed but
line 193 failed, in this case DB entry not updated but txid incremented by 1, can you fix
this inconsistency?


I think we need to add more test cases here. We need to at least address following

{{testGetTransactions}}: 1) can we test the case that to generate 40 tx, then fetch 30, 30,
we need to ensure the 2nd time returns last 10 plus first 20; 2) can we add a test case that
when the log is empty, we fetch an empty list?

{{testIncrementCount}}: we need to add the test to make sure it is in range [-1, MAX_RETRY],
currently it only tests 0 to 1.

{{testCommitTransactions}}: can we add a test case to generate 40 tx, then commit random number
of tx, then fetch 20, 20 to verify we can still get things we want?

Please let me know if this makes sense. Thank you.

> Ozone: DeleteKey-5: Implement SCM DeletedBlockLog
> -------------------------------------------------
>                 Key: HDFS-12283
>                 URL: https://issues.apache.org/jira/browse/HDFS-12283
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: ozone, scm
>            Reporter: Weiwei Yang
>            Assignee: Yuanbo Liu
>         Attachments: HDFS-12283.001.patch, HDFS-12283-HDFS-7240.001.patch
> The DeletedBlockLog is a persisted log in SCM to keep tracking container blocks which
are under deletion. It maintains info about under-deletion container blocks that notified
by KSM, and the state how it is processed. We can use RocksDB to implement the 1st version
of the log, the schema looks like
> ||TxID||ContainerName||Block List||ProcessedCount||
> |0|c1|b1,b2,b3|0|
> |1|c2|b1|3|
> |2|c2|b2, b3|-1|
> Some explanations
> # TxID is an incremental long value transaction ID for ONE container and multiple blocks
> # Container name is the name of the container
> # Block list is a list of block IDs
> # ProcessedCount is the number of times SCM has sent this record to datanode, it represents
the "state" of the transaction, it is in range of \[-1, 5\], -1 means the transaction eventually
failed after some retries, 5 is the max number times of retries.
> We need to define {{DeletedBlockLog}} as an interface and implement this with RocksDB
{{MetadataStore}} as the first version.

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