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Reuse string buffer in stringTuples.Swap (#654)

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* Reuse string buffer when swapping stringTuples

This reduces the allocs of WriteLabelIndex significantly.

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>

* Fix review comments

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>

* Add CHANGELOG entry

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>
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Ganesh Vernekar 2019-07-10 11:58:28 +05:30 committed by GitHub
parent b1cd829030
commit b5b8c9200c
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1 changed files with 10 additions and 5 deletions
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15
index/index.go
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@ -955,25 +955,30 @@ func (r *Reader) LabelNames() ([]string, error) {
type stringTuples struct { type stringTuples struct {
length int // tuple length length int // tuple length
entries []string // flattened tuple entries entries []string // flattened tuple entries
swapBuf []string
} }
func NewStringTuples(entries []string, length int) (*stringTuples, error) { func NewStringTuples(entries []string, length int) (*stringTuples, error) {
if len(entries)%length != 0 { if len(entries)%length != 0 {
return nil, errors.Wrap(encoding.ErrInvalidSize, "string tuple list") return nil, errors.Wrap(encoding.ErrInvalidSize, "string tuple list")
} }
return &stringTuples{entries: entries, length: length}, nil return &stringTuples{
entries: entries,
length: length,
}, nil
} }
func (t *stringTuples) Len() int { return len(t.entries) / t.length } func (t *stringTuples) Len() int { return len(t.entries) / t.length }
func (t *stringTuples) At(i int) ([]string, error) { return t.entries[i : i+t.length], nil } func (t *stringTuples) At(i int) ([]string, error) { return t.entries[i : i+t.length], nil }
func (t *stringTuples) Swap(i, j int) { func (t *stringTuples) Swap(i, j int) {
c := make([]string, t.length) if t.swapBuf == nil {
copy(c, t.entries[i:i+t.length]) t.swapBuf = make([]string, t.length)
}
copy(t.swapBuf, t.entries[i:i+t.length])
for k := 0; k < t.length; k++ { for k := 0; k < t.length; k++ {
t.entries[i+k] = t.entries[j+k] t.entries[i+k] = t.entries[j+k]
t.entries[j+k] = c[k] t.entries[j+k] = t.swapBuf[k]
} }
} }