pingcap / pingcap/tiflash

[Storage] Extra data copy in DeltaValueSpace

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

Description

When reading data from a DeltaPackBlock with cache, currently we need to do 2 copies:

  1. DeltaPackBlock::cache to DPBlockReader::cols_data_cache
  2. DPBlockReader::cols_data_cache to result columns

The first step is unnecessary because both DeltaPackBlock::cache and DPBlockReader::cols_data_cache are in memory.

Contributor guide

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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

Trace reads from DeltaPackBlock::cache through DPBlockReader::cols_data_cache to the result columns, focusing on the cached read path described in the issue. Confirm that the intermediate copy can be removed without changing the returned data, then run the relevant storage tests and verify cached reads still produce correct result columns.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp
Domain
database
Issue type
Refactor
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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