Details
-
Improvement
-
Status: Open
-
Major
-
Resolution: Unresolved
-
2.6.0
-
None
-
None
Description
To scale reads of hot blocks in large clusters, it would be beneficial if we could read a block across the ToR switches only once. Example scenarios are localization of binaries, MR distributed cache files for map-side joins and similar. There are multiple layers where this could be implemented (YARN service or individual apps such as MR) but I believe it is best done in HDFS or even common FileSystem to support as many use cases as possible.
The life cycle could look like this e.g. for the YARN localization scenario:
1. inputStream = fs.open(path, ..., CACHE_IN_RACK)
2. instead of reading from a remote DN directly, NN tells the client to read via the local DN1 and the DN1 creates a replica of each block.
When the next localizer on DN2 in the same rack starts it will learn from NN about the replica in DN1 and the client will read from DN1 using the conventional path.
When the application ends the AM or NM's can instruct the NN in a fadvise DONTNEED style, it can start telling DN's to discard extraneous replica.
Attachments
Issue Links
- is related to
-
YARN-5396 YARN large file broadcast service
-
- Open
-