pingcap / pingcap/tiflash

Improve calculated logical split point for partial referenced DMFile

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#5,888 1 comment 0 reactions 0 assignees View on GitHub

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type/enhancement
Dominant language
C++
Stars
1k
Forks
423
Avg merge
1d 15h
Merged PRs (30d)
24

Description

Enhancement

Suppose we have 10 packs containing identical rows:

[x, x, x, x, x, x, x, x, x, x]

When we do logical, the split point is:

               Split Point
               ↓
[x, x, x, x, x, x, x, x, x, x]
|<----------->||<----------->|
    Segment        Segment

However, if we do logical split again:

[x, x, x, x, x, x, x, x, x, x]
|<----------->||<----------->|
                     ↑
                     Do Logical Split

The calculated split point will be wrong:

       ↓ Calculated Invalid Split Point
[x, x, x, x, x, x, x, x, x, x]
|<----------->||<----------->|
                     ↑
                     Do Logical Split

In this case logical split will be fall back to Physical Split.

Contributor guide

No contributing guide indexed for this repository

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by tracing the logical split calculation for a partial referenced DMFile and reproduce the issue with 10 packs containing identical rows. Done means a repeated logical split computes a valid split point for the partial DMFile instead of falling back to a physical split.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp
Domain
databases
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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