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  1. Hadoop Common
  2. HADOOP-15016

RPC FairCallQueue Reservation Support



    • Improvement
    • Status: Open
    • Major
    • Resolution: Unresolved
    • None
    • None
    • None
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      FairCallQueue is introduced to provide RPC resource fairness among different users. In current implementation, each user is weighted equally, and the processing priority for different RPC calls are based on how many requests that user sent before. This works well when the cluster is shared among several end-users.

      However, this has some limitations when a cluster is shared among both end-users and some service jobs, like some ETL jobs which run under a service account and need to issue lots of RPC calls. When NameNode becomes quite busy, this set of jobs can be easily backoffed and low-prioritied. We cannot simply treat this type jobs as "bad" user who randomly issues too many calls, as their calls are normal calls. Also, it is unfair to weight a end-user and a heavy service user equally when allocating RPC resources.

      One idea here is to introduce reservation support to RPC resources. That is, for some services, we reserve some RPC resources for their calls. This idea is very similar to how YARN manages CPU/memory resources among different resource queues. A little more details here: Along with existing FairCallQueue setup (like using 4 queues with different priorities), we would add some additional special queues, one for each special service user. For each special service user, we provide a guarantee RPC share (like 10% which can be aligned with its YARN resource share), and this percentage can be converted to a weight used in WeightedRoundRobinMultiplexer. A quick example, we have 4 default queues with default weights (8, 4, 2, 1), and two special service users (user1 with 10% share, and user2 with 15% share). So finally we'll have 6 queues, 4 default queues (with weights 8, 4, 2, 1) and 2 special queues (user1Queue weighted 15*10%/75%=2, and user2Queue weighted 15*15%/75%=3).

      For new coming RPC calls from special service users, they will be put directly to the corresponding reserved queue; for other calls, just follow current implementation.

      By default, there is no special user and all RPC requests follow existing FairCallQueue implementation.

      Would like to hear more comments on this approach; also want to know any other better solutions? Will put a detailed design once get some early comments.


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              ywskycn Wei Yan
              ywskycn Wei Yan
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