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Intern LowCardinality Row values to reduce string allocations #1790

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Intern LowCardinality Row values to reduce string allocations #1790

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bbdcca9
Intern LowCardinality Row values to reduce string allocations
Onyx2406 Mar 8, 2026
0980f43
refactor: use eagerly populated slice instead of lazy map for row cache
Onyx2406 Mar 10, 2026
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13 changes: 13 additions & 0 deletions lib/column/lowcardinality.go
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,8 @@ type LowCardinality struct {
keys32 UInt32
keys64 UInt64

rowCache []any

append struct {
keys []int
index map[any]int
Expand All @@ -59,6 +61,7 @@ func (col *LowCardinality) Reset() {
col.keys16.Reset()
col.keys32.Reset()
col.keys64.Reset()
col.rowCache = nil
col.append.index = make(map[any]int)
col.append.keys = col.append.keys[:0]
}
Expand Down Expand Up @@ -96,6 +99,16 @@ func (col *LowCardinality) Row(i int, ptr bool) any {
if idx == 0 && col.nullable {
return nil
}
if !ptr {
if col.rowCache == nil {
n := col.index.Rows()
col.rowCache = make([]any, n)
for j := 0; j < n; j++ {
col.rowCache[j] = col.index.Row(j, false)
}
}
return col.rowCache[idx]
}
return col.index.Row(idx, ptr)
}

Expand Down