Also limit the size of block in bytes when processing queries in TiFlash
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- Dominant language
- C++
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- Merged PRs (30d)
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Description
Currently, TiFlash processes data in Blocks, and use max_block_size to suggest the size of one block. max_block_size only suggest the rows, which is not quite enough. For example, when there are too many columns, only limits the rows of block can still cause too much memory is used. ClickHouse already supports preferred_block_size_bytes and we should follow.
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First steps
- Read the whole issue, then the project's contributing guide.
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- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by tracing how TiFlash applies max_block_size while processing query Blocks, then compare the requested behavior with ClickHouse's preferred_block_size_bytes documentation. Done means blocks are constrained by both row count and byte size, with tests or measurements covering wide rows and preventing excessive memory use.
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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