[jira] [Commented] (HDFS-13079) Provide a config to start namenode in safemode state upto a certain transaction id

["Hanisha Koneru (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-13079?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16471282#comment-16471282 ] 

Hanisha Koneru commented on HDFS-13079:
---------------------------------------

Thanks [~shashikant] for updating the patch.

{{FSImageTransactionalStorageInspector#getImagesWithTransactionId}} should return the images with txId << user supplied txId, right.

Lets say we have three fsImages - fsImage_0012, fsImage_0025 and fsImage_0040 and we want to load uptill txId 30. The function above should return both fsImage_0025 and fsImage_0012, and in that order.
{code}
179      ret = new LinkedList<FSImageFile>();
180      for (FSImageFile img : foundImages) {
181        if (ret.isEmpty() && txid <= img.txId) {
182         ret.add(img);
183        }
{code}
In the if condition above, if txId (30) is <= img.txId (40), that image should not be returned. 




> Provide a config to start namenode in safemode state upto a certain transaction id
> ----------------------------------------------------------------------------------
>
>                 Key: HDFS-13079
>                 URL: https://issues.apache.org/jira/browse/HDFS-13079
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>            Reporter: Mukul Kumar Singh
>            Assignee: Shashikant Banerjee
>            Priority: Major
>         Attachments: HDFS-13079.001.patch, HDFS-13079.002.patch, HDFS-13079.003.patch
>
>
> In some cases it necessary to rollback the Namenode back to a certain transaction id. This is especially needed when the user issues a {{rm -Rf -skipTrash}} by mistake.
> Rolling back to a transaction id helps in taking a peek at the filesystem at a particular instant. This jira proposes to provide a configuration variable using which the namenode can be started upto a certain transaction id. The filesystem will be in a readonly safemode which cannot be overridden manually. It will only be overridden by removing the config value from the config file. Please also note that this will not cause any changes in the filesystem state, the filesystem will be in safemode state and no changes to the filesystem state will be allowed.
> Please note that in case a checkpoint has already happened and the requested transaction id has been subsumed in an FSImage, then the namenode will be started with the next nearest transaction id. Further FSImage files and edits will be ignored.
> If the checkpoint hasn't happen then the namenode will be started with the exact transaction id.



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