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import into merge stage is extremely slow for large datasets due to suboptimal resource usage #60375

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@shaoxiqian

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

  1. datesize 8T with about 48 billion rows
  2. DXF is enabled
  3. import into xxx from s3:xxx

2. What did you expect to see? (Required)

The merge phase should be optimized to make full use of all available TiDB resources

3. What did you see instead (Required)

Only 2 subtasks were allocated, and while one finishes the merge step quickly, the other takes nearly 2 hours.
[next-step=merge-sort] [subtask-count=2]
Image
Image

4. What is your TiDB version? (Required)

v8.5.1

Activity

  1. added
    type/bugThe issue is confirmed as a bug.
    and removed
    type/bugThe issue is confirmed as a bug.
    on Apr 2, 2025
  2. self-assigned this
    on Apr 3, 2025
  3. added a commit that references this issue on May 24, 2025
    5a00a10
  4. added a commit that references this issue on Jul 6, 2025
    b7e7c2d
  5. added a commit that references this issue on Jul 8, 2025
    2e8c569
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affects-8.1This bug affects the 8.1.x(LTS) versions.affects-8.5This bug affects the 8.5.x(LTS) versions.component/ddlThis issue is related to DDL of TiDB.component/importseverity/majortype/bugThe issue is confirmed as a bug.

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