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  1. Core Server
  2. SERVER-60138

Improve the allocated memory for getMore commands

    • Type: Icon: Improvement Improvement
    • Resolution: Fixed
    • Priority: Icon: Major - P3 Major - P3
    • 5.2.0
    • Affects Version/s: None
    • Component/s: Query Execution
    • Labels:
    • Fully Compatible
    • QE 2021-10-04, QE 2021-10-18, QE 2021-11-01
    • 120

      We want to improve the reservation of the maximum size versus when we should reserve something smaller for the getMore command. Here's a pragmatic approach:

      1. For a normal cursor with no explicit batch size, 16MB.
      2. For a normal cursor with explicit batch size, perhaps 8MB.
      3. For a tailable cursor, which may often return 0 or a small number of results, perhaps 4MB.

      We can better fine-tune the above heuristics based on the performance benchmarks in PERF-2565 and PERF-2566. Another worthwhile question that's worth answering as part of this task and its related experiments is that "What happens if we do not do pre-allocation at all"?

            mohammad.dashti@mongodb.com Mohammad Dashti (Inactive)
            mohammad.dashti@mongodb.com Mohammad Dashti (Inactive)
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