make StateCompute not write the output state to the blockstore.

api/api_full.go

@@ -8,7 +8,7 @@ import (
 
 	"github.com/google/uuid"
 	"github.com/ipfs/go-cid"
-	blocks "github.com/ipfs/go-libipfs/blocks"
+	"github.com/ipfs/go-libipfs/blocks"
 	"github.com/libp2p/go-libp2p/core/peer"
 
 	"github.com/filecoin-project/go-address"
@@ -606,6 +606,9 @@ type FullNode interface {
 	//
 	// Messages in the `apply` parameter must have the correct nonces, and gas
 	// values set.
+	//
+	// This method does not write the resulting state to the blockstore. Usually
+	// that state will already exist.
 	StateCompute(context.Context, abi.ChainEpoch, []*types.Message, types.TipSetKey) (*ComputeStateOutput, error) //perm:read
 	// StateVerifierStatus returns the data cap for the given address.
 	// Returns nil if there is no entry in the data cap table for the

chain/stmgr/utils.go

@@ -17,6 +17,7 @@ import (
 	gstStore "github.com/filecoin-project/go-state-types/store"
 
 	"github.com/filecoin-project/lotus/api"
+	"github.com/filecoin-project/lotus/blockstore"
 	init_ "github.com/filecoin-project/lotus/chain/actors/builtin/init"
 	"github.com/filecoin-project/lotus/chain/actors/builtin/system"
 	"github.com/filecoin-project/lotus/chain/actors/policy"
@@ -86,13 +87,14 @@ func ComputeState(ctx context.Context, sm *StateManager, height abi.ChainEpoch,
 		// future. It's not guaranteed to be accurate... but that's fine.
 	}
 
+	buf := blockstore.NewBuffered(sm.cs.StateBlockstore())
 	r := rand.NewStateRand(sm.cs, ts.Cids(), sm.beacon, sm.GetNetworkVersion)
 	vmopt := &vm.VMOpts{
 		StateBase:      base,
 		Epoch:          height,
 		Timestamp:      ts.MinTimestamp(),
 		Rand:           r,
-		Bstore:         sm.cs.StateBlockstore(),
+		Bstore:         buf,
 		Actors:         sm.tsExec.NewActorRegistry(),
 		Syscalls:       sm.Syscalls,
 		CircSupplyCalc: sm.GetVMCirculatingSupply,

cmd/lotus-shed/chain.go

@@ -77,6 +77,10 @@ var computeStateRangeCmd = &cli.Command{
 			return err
 		}
 
+		// StateCompute doesn't write the resulting state to the blockstore,
+		// hence state write overheads that would otherwise apply during block
+		// validation will not be observed here.
+
 		fmt.Printf("computing tipset at height %d (start)\n", startTs.Height())
 		if _, err := api.StateCompute(ctx, startTs.Height(), nil, startTs.Key()); err != nil {
 			return err