planner: introduce new cost formula for Selection/TableScan/IndexScan #35378
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Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/09678e9a964beb3b01a3ec19c75929980961c033 |
planner/core/plan_cost.go
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| scanFactor = p.ctx.GetSessionVars().GetDescScanFactor(p.Table) | ||
| } | ||
| } | ||
| rowSize := math.Max(p.getScanRowSize(), 2.0) |
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Why cannot rowSize exceed 2?
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To guarantee logRowSize >= 1.
| } | ||
| } | ||
| rowSize := math.Max(p.getScanRowSize(), 2.0) | ||
| logRowSize := math.Log2(rowSize) |
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Log2 in the formula is based on experiment results?
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YES, I'll add some comments here.
| var scanFactor float64 | ||
| switch taskType { | ||
| case property.MppTaskType: // use a dedicated scan-factor for TiFlash | ||
| scanFactor = p.ctx.GetSessionVars().GetTiFlashScanFactor() |
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Here we assume that there is little performance difference between Scan and DescScan on TiFlash.
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Yes, no need to distinguish Scan and DescScan for TiFlash for now. I'll add some comments.
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Some comments were added, PTAL @xuyifangreeneyes |
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/run-unit-test |
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This pull request has been accepted and is ready to merge. Commit hash: d59348e
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This pull request has been accepted and is ready to merge. Commit hash: d59348e
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What problem does this PR solve?
Issue Number: ref #35240
Problem Summary: introduce new cost formula for Selection/TableScan/IndexScan
What is changed and how it works?
Introduce new cost formula for Selection/TableScan/IndexScan.
On cost model ver2:
rows*cpu-factor->rows*num-filters*cpu-factor; use a dedicatedcpu-factorfor TiFlash;rows*row-size*scan-factor->rows*log(row-size)*scan-factor; use a dedicatedscan-factorfor TiFlash;rows*row-size*scan-factor->rows*log(row-size)*scan-factor;I'll add tests after finishing cost model ver2.
Check List
Tests
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Release note
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