Optimize wide table memory usage
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type/enhancement
- Dominant language
- C++
- Stars
- 1k
- Forks
- 423
- Avg merge
- 1d 15h
- Merged PRs (30d)
- 24
Description
During delta merge, segment merge, and split, we use DMFileBlockOutputStream to generate new DTFiles. And the blocks written into the stream contain all columns. It can cause high memory usage if the table has many columns. Especially for wide tables.
- A single pack(or Block) can be large in size. Each pack contains fixed rows. When the size of each row grows, the size of packs grows.
- More importantly, we have to put all columns of all packs of the Delta layer into memory.
Contributor guide
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with DMFileBlockOutputStream and trace its use during delta merge, segment merge, and split when generating DTFiles. Measure how packs and columns are retained in memory, then verify that the resulting DTFiles remain correct while peak memory usage is reduced.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- cpp
- Domain
- databases
- Issue type
- Refactor
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 35/100