perf: optimize MemoryStorage.Compact method by improving memory allocation

[1911860538]

Avoiding the use of append, and directly copying remaining entries to a new slice for better performance.

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @1911860538. Thanks for your PR.

I'm waiting for a etcd-io member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[ahrtr]

/ok-to-test

[1911860538]

/ok-to-test

My code update appears to be leading to unexpected issues because the original logic only copied the Term and Index of the i-th element, whereas after my modification, it now copies all fields of the i-th element.
Perhaps the following code modification is more appropriate?

ents := make([]pb.Entry, uint64(len(ms.ents)) - i)
// Only copy Index and Term of the compact index entry (first entry).
// These fields are sufficient for log matching in the Raft algorithm,
// while Type and Data are not needed since the entry's command has
// already been applied to the state machine.
ents[0].Index = ms.ents[i].Index
ents[0].Term = ms.ents[i].Term
copy(ents[1:], ms.ents[i+1:])

[1911860538]

/ok-to-test

My code update appears to be leading to unexpected issues because the original logic only copied the Term and Index of the i-th element, whereas after my modification, it now copies all fields of the i-th element. Perhaps the following code modification is more appropriate?

ents := make([]pb.Entry, uint64(len(ms.ents)) - i)
// Only copy Index and Term of the compact index entry (first entry).
// These fields are sufficient for log matching in the Raft algorithm,
// while Type and Data are not needed since the entry's command has
// already been applied to the state machine.
ents[0].Index = ms.ents[i].Index
ents[0].Term = ms.ents[i].Term
copy(ents[1:], ms.ents[i+1:])

The Benchmark results of my local code indicate that this code modification results in a slight performance boost, whereas the previous code changes showed no performance improvement.
Therefore, I am going to close this pull request.

package entry_compact

import (
	"bytes"
	"testing"
)

type Entry struct {
	Term  uint64
	Index uint64
	Type  int32
	Data  []byte
}

const (
	compactIndex = 100
	entriesLen   = 1000
)

func getEntries(length int) []Entry {
	src := make([]Entry, length)
	for i := range length {
		src[i] = Entry{
			Term:  uint64(i),
			Index: uint64(i),
			Type:  int32(i),
			Data:  []byte{'0'},
		}
	}
	return src
}

func copy1(src []Entry, index int) []Entry {
	dst := make([]Entry, 1, len(src)-index)
	dst[0].Term = src[0].Term
	dst[0].Index = src[0].Index
	dst = append(dst, src[index+1:]...)
	return dst
}

func copy2(src []Entry, index int) []Entry {
	dst := make([]Entry, len(src)-index)
	dst[0].Term = src[0].Term
	dst[0].Index = src[0].Index
	copy(dst[1:], src[index+1:])
	return dst
}

func copy3(src []Entry, index int) []Entry {
	dst := make([]Entry, len(src)-index)
	copy(dst, src[index:])
	return dst
}

func BenchmarkCopy1(b *testing.B) {
	src := getEntries(entriesLen)
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		copy1(src, compactIndex)
	}
}

func BenchmarkCopy2(b *testing.B) {
	src := getEntries(entriesLen)
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		copy2(src, compactIndex)
	}
}

func BenchmarkCopy3(b *testing.B) {
	src := getEntries(entriesLen)
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		copy3(src, compactIndex)
	}
}

func TestSame(t *testing.T) {
	src := getEntries(entriesLen)
	c1 := copy1(src, compactIndex)
	c2 := copy2(src, compactIndex)
	if len(c1) != len(c2) {
		t.Fatal("copied slices are not the same length")
	}
	for i := range c1 {
		c1i := c1[i]
		c2i := c2[i]
		if c1i.Term != c2i.Term || c1i.Index != c2i.Index || c1i.Type != c2i.Type || bytes.Compare(c1i.Data, c2i.Data) != 0 {
			t.Fatal("copied items are not same")
		}
	}
}

Test output

=== RUN   TestSame
--- PASS: TestSame (0.00s)
PASS

Process finished with the exit code 0

Benchmark output

goos: darwin
goarch: arm64
pkg: test_code/entry_compact
cpu: Apple M3 Pro
BenchmarkCopy1
BenchmarkCopy1-11    	  436888	      2679 ns/op	   49152 B/op	       1 allocs/op
BenchmarkCopy2
BenchmarkCopy2-11    	  452683	      2652 ns/op	   49152 B/op	       1 allocs/op
BenchmarkCopy3
BenchmarkCopy3-11    	  446326	      2681 ns/op	   49152 B/op	       1 allocs/op
PASS

Process finished with the exit code 0