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https://issues.apache.org/jira/browse/HDFS-5158?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13764061#comment-13764061
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Aaron T. Myers commented on HDFS-5158:
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bq. "CachedPath" would be a misleading name, since we may or may not actually
be able to cache the path entries in PathCache. Resources aren't infinite. Bear
in mind that there are going to be other caches that don't operate by path
name-- one example is the LRU cache we've talked about. PathCache, as well as
PathCacheDirective, PathCacheEntry, etc. are named the way they are to
distinguish them from the (future) LruCacheDirective, etc. classes which don't
exist yet.
Even with this justification and the context of the future "Lru*" classes,
there's just no way you can get away from people interpreting "path cache" to
mean "a cache of paths," which I find to be vastly more misleading/confusing
than "CachedPath" would be. How do you feel about "CachePath" (no 'd') as I
also suggested? That doesn't necessarily imply that anything is already cached,
and also appears to work with the future classes you mentioned here, e.g.
CacheLruDirective, CacheLruEntry, etc.
bq. For example, Impala or Hive may want to add many cache directives at once.
I'm a tad skeptical this will in fact be the case, given that the caching
directive can potentially provide a directory as the path, but it seems fairly
harmless to leave in the RPCs that take lists as arguments.
bq. We discussed this on HDFS-5052. The short summary is that paths don't
uniquely identify path cache directives. You can have multiple directives that
apply to the same path.
Could you even have multiple directives for the same path within a single pool?
Or would the (pool, path) pair uniquely identify the cache directive?
bq. I did not change the prefix in this patch. Does it make sense to put the
prefix change stuff in another JIRA? It seems like it will be a bigger effort,
if we're moving the -addCachePool, etc. commands as well.
I'd personally do it in this JIRA; it really shouldn't be that much work. But,
if you feel strongly about it, you can do it in a separate JIRA if you want.
> add command-line support for manipulating cache directives
> ----------------------------------------------------------
>
> Key: HDFS-5158
> URL: https://issues.apache.org/jira/browse/HDFS-5158
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode, namenode
> Affects Versions: HDFS-4949
> Reporter: Colin Patrick McCabe
> Assignee: Colin Patrick McCabe
> Attachments: HDFS-5158-caching.003.patch,
> HDFS-5158-caching.004.patch, HDFS-5158-caching.005.patch,
> HDFS-5158-caching.006.patch
>
>
> We should add command-line support for creating, removing, and listing cache
> directives.
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