fix: change the batch size to avoid buffering too much

Otherwise, the max outstanding blocks/size depends on the number of cores.

batch.go

@@ -8,10 +8,10 @@ import (
 	cid "github.com/ipfs/go-cid"
 )
 
-// ParallelBatchCommits is the number of batch commits that can be in-flight before blocking.
+// parallelBatchCommits is the number of batch commits that can be in-flight before blocking.
 // TODO(ipfs/go-ipfs#4299): Experiment with multiple datastores, storage
 // devices, and CPUs to find the right value/formula.
-var ParallelBatchCommits = runtime.NumCPU() * 2
+var parallelCommits = runtime.NumCPU()
 
 // ErrNotCommited is returned when closing a batch that hasn't been successfully
 // committed.
@@ -32,11 +32,15 @@ func NewBatch(ctx context.Context, na NodeAdder, opts ...BatchOption) *Batch {
 	for _, o := range opts {
 		o(&bopts)
 	}
+
+	// Commit numCPU batches at once, but split the maximum buffer size over all commits in flight.
+	bopts.maxSize /= parallelCommits
+	bopts.maxNodes /= parallelCommits
 	return &Batch{
 		na:            na,
 		ctx:           ctx,
 		cancel:        cancel,
-		commitResults: make(chan error, ParallelBatchCommits),
+		commitResults: make(chan error, parallelCommits),
 		opts:          bopts,
 	}
 }
@@ -78,7 +82,7 @@ func (t *Batch) asyncCommit() {
 	if numBlocks == 0 {
 		return
 	}
-	if t.activeCommits >= ParallelBatchCommits {
+	if t.activeCommits >= parallelCommits {
 		select {
 		case err := <-t.commitResults:
 			t.activeCommits--
@@ -206,14 +210,16 @@ var defaultBatchOptions = batchOptions{
 	maxNodes: 128,
 }
 
-// MaxSizeBatchOption sets the maximum size of a Batch.
+// MaxSizeBatchOption sets the maximum amount of buffered data before writing
+// blocks.
 func MaxSizeBatchOption(size int) BatchOption {
 	return func(o *batchOptions) {
 		o.maxSize = size
 	}
 }
 
-// MaxNodesBatchOption sets the maximum number of nodes in a Batch.
+// MaxNodesBatchOption sets the maximum number of buffered nodes before writing
+// blocks.
 func MaxNodesBatchOption(num int) BatchOption {
 	return func(o *batchOptions) {
 		o.maxNodes = num

batch_test.go

@@ -139,10 +139,10 @@ func TestBatchOptions(t *testing.T) {
 	wantMaxNodes := 500
 	d := newTestDag()
 	b := NewBatch(ctx, d, MaxSizeBatchOption(wantMaxSize), MaxNodesBatchOption(wantMaxNodes))
-	if b.opts.maxSize != wantMaxSize {
+	if b.opts.maxSize != wantMaxSize/parallelCommits {
 		t.Fatalf("maxSize incorrect, want: %d, got: %d", wantMaxSize, b.opts.maxSize)
 	}
-	if b.opts.maxNodes != wantMaxNodes {
+	if b.opts.maxNodes != wantMaxNodes/parallelCommits {
 		t.Fatalf("maxNodes incorrect, want: %d, got: %d", wantMaxNodes, b.opts.maxNodes)
 	}
 }

go.mod

@@ -1,9 +1,10 @@
 module github.com/ipfs/go-ipld-format
 
-go 1.14
-
 require (
 	github.com/ipfs/go-block-format v0.0.2
 	github.com/ipfs/go-cid v0.0.2
+	github.com/libp2p/go-buffer-pool v0.0.2 // indirect
 	github.com/multiformats/go-multihash v0.0.1
 )
+
+go 1.13

go.sum

@@ -10,6 +10,8 @@ github.com/ipfs/go-cid v0.0.2 h1:tuuKaZPU1M6HcejsO3AcYWW8sZ8MTvyxfc4uqB4eFE8=
 github.com/ipfs/go-cid v0.0.2/go.mod h1:GHWU/WuQdMPmIosc4Yn1bcCT7dSeX4lBafM7iqUPQvM=
 github.com/ipfs/go-ipfs-util v0.0.1 h1:Wz9bL2wB2YBJqggkA4dD7oSmqB4cAnpNbGrlHJulv50=
 github.com/ipfs/go-ipfs-util v0.0.1/go.mod h1:spsl5z8KUnrve+73pOhSVZND1SIxPW5RyBCNzQxlJBc=
+github.com/libp2p/go-buffer-pool v0.0.2 h1:QNK2iAFa8gjAe1SPz6mHSMuCcjs+X1wlHzeOSqcmlfs=
+github.com/libp2p/go-buffer-pool v0.0.2/go.mod h1:MvaB6xw5vOrDl8rYZGLFdKAuk/hRoRZd1Vi32+RXyFM=
 github.com/minio/blake2b-simd v0.0.0-20160723061019-3f5f724cb5b1 h1:lYpkrQH5ajf0OXOcUbGjvZxxijuBwbbmlSxLiuofa+g=
 github.com/minio/blake2b-simd v0.0.0-20160723061019-3f5f724cb5b1/go.mod h1:pD8RvIylQ358TN4wwqatJ8rNavkEINozVn9DtGI3dfQ=
 github.com/minio/sha256-simd v0.0.0-20190131020904-2d45a736cd16 h1:5W7KhL8HVF3XCFOweFD3BNESdnO8ewyYTFT2R+/b8FQ=