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rui@joyent.com,rob.johnston@joyent.com
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RFD 170 Manta Picker Component

This RFD describes the Manta Picker component.

Introduction

In mantav1, the "picker" is part of the manta-muskie (webapi) component. It is responsible for selecting the list of destination storage nodes for new objects on a PUT request. It functions by querying the manta_storage bucket on shard 1 at a default interval of 30s. Recently, we have found that picker can overload the shard 1 Moray instance MANTA-4091.

The new Rebalancer project introduces yet another consumer of the data in the manta_storage bucket. For mantav2, in order to avoid hot-shard issues that would be caused by all of the rebalancer and muskie service instances hitting shard 1 to get storage utilization data, the picker functionality has been split out into a separate service (manta-picker). This new service provides an interface for retrieving a cached view of the contents of the manta_storage bucket via the /poll REST endpoint. The Rebalancer will be designed to leverage the manta-picker and the mantav2 equivalent of muskie (buckets-api) will be modified to use the manta-picker service MANTA-4821.

Requirements

  • Picker instances should report their availability to DNS via registrar.
  • Multiple picker zones can be deployed for scalability.
  • Picker tunables should be added to SAPI, and controlled there.

Interfaces

GetSharks (GET /poll)

Returns a list of storage nodes found in the manta_storage bucket, sorted by the manta_storage_id field. Because the list of makos can be quite large, this endpoint enforces pagination to limit the response size.

poll will implement a cursor-based pagination scheme using the mako's manta_storage_id as the cursor value.`

Inputs

Field Type Description
after_id String return results for mako with a storage id greater than "after_id" (default="0")
only_id String return result for only the mako specified by the storage id "only_id"
limit Number max number of results to return (default/max = 500)

Example

Get up to the first 100 results:

/poll?limit=100

Get up to the next 100 results:

/poll?limit=100&after_id=<last_id>

FlushCache (POST /flush)

Forces the picker's cached view of the manta_storage bucket to be immediately invalidated and refreshed. The only intended consumer of this API is the Rebalancer, which will call this API after marking a storage node as read-only, prior to evacuating the objects on it.

This interfaces takes no input parameters.

Assumptions and Risks

  • A given Manta deployment requires significantly less than M picker components where M is the total number of muskie processes (M = Muskie zones * Muskie SMF instances).
  • The Picker's intermittent updates will provide a sufficiently current view for use with the Rebalancer's selection of a destination storage node.