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  1. Core Server
  2. SERVER-57057

Reduce routing info refreshes on the mergeChunks path

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    Details

    • Type: Improvement
    • Status: Closed
    • Priority: Major - P3
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 5.1.0, 4.2.15, 4.4.7, 5.0.0-rc1, 4.0.26
    • Component/s: None
    • Labels:
      None
    • Backwards Compatibility:
      Fully Compatible
    • Backport Requested:
      v5.0, v4.4, v4.2, v4.0
    • Sprint:
      Sharding EMEA 2021-05-31

      Description

       
      The current mergeChunks path is very inefficient because:

      It performs three sequential refreshes (router, shard-pre-merge and shard-post-merge)

      All this makes the mergeChunks command very expensive both from latency and from impact on the config server points of view.

      It would be much better if:

      • The router command:
        • Didn't do a refresh on entry, but relied on the cached information and the shardVersion (this has backwards compatibility implications)
      • The shard command (in order of importance):
        • Just checked the major shardVersion (for routing correctness, i.e., to make sure this shard owns that range)
        • Only did a refresh on the shard if the chunk bounds that the router sent didn't match with the cached info (this can only happen if a previous merge committed against the ConfigServer, but failed to refresh)

           

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              Assignee:
              simon.gratzer Simon Gratzer
              Reporter:
              simon.gratzer Simon Gratzer
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                Created:
                Updated:
                Resolved: