Hi Vinayakumar,
If you append to a block which has hard-links, then it will get copied on
write at the DataNode. See this code:
/**
* Make a copy of the block if this block is linked to an existing
* snapshot. This ensures that modifying this block does not modify
* data in any existing snapshots.
* @param block Block
* @param numLinks Detach if the number of links exceed this value
* @throws IOException
* @return - true if the specified block was detached
*/
public boolean detachBlock(Block block, int numLinks) throws IOException {
...
-Todd
On Thu, Nov 15, 2012 at 11:00 PM, Vinayakumar B <vinayakuma...@huawei.com>wrote:
> Hi All,
>
>
>
> I have a question here.
>
>
>
> Scenario:
>
> --------------
>
> 1. Cluster is having some blocks and its upgraded.
>
> 2. As part of upgrade, in datanode side hardlinks are created for all
> blocks.
>
> 3. Now one of the block is appended with the some more data
>
> 4. Do rollback
>
>
>
> Now what happens for the appended data..?
>
>
>
> Since blocks are hardlinked, changes on the original file will reflect on
> the hardlinked file inside previous also.
>
>
>
> So changes to a appended block after upgrade will not be reverted after
> rollback.
>
>
>
> How to handle this case..?
>
>
>
> Any thoughts..?
>
>
>
> Regards,
>
> Vinayakumar B.,
>
>
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--
Todd Lipcon
Software Engineer, Cloudera
