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Improve *deduplicatingSlice.ingest performance #4037

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acbfc9b
Add benchmark for `*PartitionWriter.WriteProfileSymbols`
inkel Mar 21, 2025
196a1a0
Refactor `*PartitionWriter.WriteProfileSymbols` for DRY
inkel Mar 21, 2025
fc7e5d2
Create rewriting map with maximum capacity
inkel Mar 21, 2025
44cf7d9
Use temp slice to append only once
inkel Mar 21, 2025
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6 changes: 4 additions & 2 deletions pkg/phlaredb/symdb/dedup_slice.go
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Original file line number Diff line number Diff line change
Expand Up @@ -254,7 +254,7 @@ func (s *deduplicatingSlice[M, K, H]) Size() uint64 {

func (s *deduplicatingSlice[M, K, H]) ingest(elems []M, rewriter *rewriter) {
var (
rewritingMap = make(map[int64]int64)
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Good find, this will give us a right sized map every time.

rewritingMap = make(map[int64]int64, len(elems))
missing = int64SlicePool.Get()
)
missing = missing[:0]
Expand All @@ -279,6 +279,7 @@ func (s *deduplicatingSlice[M, K, H]) ingest(elems []M, rewriter *rewriter) {
if len(missing) > 0 {
s.lock.Lock()
posSlice := int64(len(s.slice))
misSlice := make([]M, 0, len(missing))
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@simonswine simonswine Mar 21, 2025 •
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Rather than using the extra slice you can also just grow the underlying slice, you might overgrow it but you can get rid of misSlice entirely.

Suggested change
misSlice := make([]M, 0, len(missing))
s.slice = slices.Grow(s.slice, len(missing))

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Ah, that's probably even better! I'll refactor to use this and see what the benchmark says.

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Did you mean slices.GrowLen instead? Anyway, I've tested calling this function and then comparing both results and got this:

$ benchstat bench.pw-writeprofilesymbols-misslice.log bench.pw-writeprofilesymbols-slicesgrowlen.log
goos: darwin
goarch: arm64
pkg: github.com/grafana/pyroscope/pkg/phlaredb/symdb
cpu: Apple M1 Pro
                                       │ bench.pw-writeprofilesymbols-misslice.log │ bench.pw-writeprofilesymbols-slicesgrowlen.log │
                                       │                  sec/op                   │         sec/op           vs base               │
PartitionWriter_WriteProfileSymbols-10                                 504.0µ ± 1%               515.7µ ± 1%  +2.34% (p=0.001 n=20)

                                       │ bench.pw-writeprofilesymbols-misslice.log │ bench.pw-writeprofilesymbols-slicesgrowlen.log │
                                       │                   B/op                    │          B/op           vs base                │
PartitionWriter_WriteProfileSymbols-10                                600.8Ki ± 0%             714.7Ki ± 0%  +18.95% (p=0.000 n=20)

                                       │ bench.pw-writeprofilesymbols-misslice.log │ bench.pw-writeprofilesymbols-slicesgrowlen.log │
                                       │                 allocs/op                 │        allocs/op         vs base               │
PartitionWriter_WriteProfileSymbols-10                                 2.176k ± 0%               2.206k ± 0%  +1.38% (p=0.000 n=20)

Surprisingly, growing s.slice is actually slower and consumes more memory 🤔

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@simonswine simonswine Mar 25, 2025 •
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No GrowLen is not the same function, as it will take the total length of slices, rather than how much more space should be available, you either need to adapt the size of that or import origslices "slices" and use slices.Grow(xx)

for _, pos := range missing {
// check again if element exists
k := s.helper.key(elems[pos])
Expand All @@ -288,12 +289,13 @@ func (s *deduplicatingSlice[M, K, H]) ingest(elems []M, rewriter *rewriter) {
}

// add element to slice/map
s.slice = append(s.slice, s.helper.clone(elems[pos]))
misSlice = append(misSlice, s.helper.clone(elems[pos]))
s.lookup[k] = posSlice
rewritingMap[int64(s.helper.setID(uint64(pos), uint64(posSlice), &elems[pos]))] = posSlice
posSlice++
s.size.Add(s.helper.size(elems[pos]))
}
s.slice = append(s.slice, misSlice...)
s.lock.Unlock()
}

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20 changes: 20 additions & 0 deletions pkg/phlaredb/symdb/symdb_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -227,3 +227,23 @@ func TestWritePartition(t *testing.T) {
`
require.Equal(t, expected, resolved.String())
}

func BenchmarkPartitionWriter_WriteProfileSymbols(b *testing.B) {
b.ReportAllocs()

p, err := pprof.OpenFile("testdata/profile.pb.gz")
require.NoError(b, err)
p.Normalize()
cfg := DefaultConfig().WithDirectory(b.TempDir())

db := NewSymDB(cfg)

for i := 0; i < b.N; i++ {
b.StopTimer()
newP := p.CloneVT()
pw := db.PartitionWriter(uint64(i))
b.StartTimer()

pw.WriteProfileSymbols(newP)
}
}
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