[
https://issues.apache.org/jira/browse/HDFS-7758?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14319063#comment-14319063
]
Colin Patrick McCabe commented on HDFS-7758:
--------------------------------------------
Thanks for taking this on, Eddy. I agree with [~jpallas]'s comment here...
please make a static method in {{FsVolumeReference}} like {{releaseAll}} if you
need a helper method to release a collection of refs.
Do we have a plan for removing {{FsDatasetSpi#getVolume}}? It seems that this
interface has a lot of the same issues as {{FsDatasetImpl#getVolumes}}. I
think it's fine to do this in a follow-up JIRA, but we should figure out what
we're doing with that.
I don't think we should have a {{FsDatasetSpi#getNumVolumes}} method. It just
encourages people to do bad things like rely on the number of volumes staying
the same. This is no longer true in a world of hotplug. I see that you have
made the same error here yourself:
{code}
+ int numVolumes = fds.getNumVolumes();
+ int index = rand.nextInt(numVolumes - 1);
long id = getFreeBlockId();
+ try (FsVolumeReference ref = fds.getVolumeRef(index) ) {
+ File finalizedDir = ref.getVolume().getFinalizedDir(bpid);
+ File file = new File(finalizedDir, getBlockFile(id));
+ if (file.createNewFile()) {
+ LOG.info("Created block file " + file.getName());
+ }
{code}
What's going to happen here if the number of volumes changes in between
{{getNumVolumes}} and {{getVolumeRef}}? Instead of doing this, just add an
FSDatasetSpi method to select a random volume (that returns a ref).
> Retire FsDatasetSpi#getVolumes() and use FsDatasetSpi#getVolumeRefs() instead
> -----------------------------------------------------------------------------
>
> Key: HDFS-7758
> URL: https://issues.apache.org/jira/browse/HDFS-7758
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Affects Versions: 2.6.0
> Reporter: Lei (Eddy) Xu
> Assignee: Lei (Eddy) Xu
> Attachments: HDFS-7758.000.patch
>
>
> HDFS-7496 introduced reference-counting the volume instances being used to
> prevent race condition when hot swapping a volume.
> However, {{FsDatasetSpi#getVolumes()}} can still leak the volume instance
> without increasing its reference count. In this JIRA, we retire the
> {{FsDatasetSpi#getVolumes()}} and propose {{FsDatasetSpi#getVolumeRefs()}}
> and etc. method to access {{FsVolume}}. Thus it makes sure that the consumer
> of {{FsVolume}} always has correct reference count.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
