[#188] engine: Refactor shard evacuation

Resolve funlen and gocognit linter for StorageEngine.Evacuate method

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/local_object_storage/engine/evacuate.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 
+	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/core/object"
 	meta "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/metabase"
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/shard"
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util"
@@ -57,35 +58,89 @@ var errMustHaveTwoShards = errors.New("must have at least 1 spare shard")
 
 // Evacuate moves data from one shard to the others.
 // The shard being moved must be in read-only mode.
-//
-// nolint: funlen, gocognit
 func (e *StorageEngine) Evacuate(prm EvacuateShardPrm) (EvacuateShardRes, error) {
-	sidList := make([]string, len(prm.shardID))
+	shardIDs := make([]string, len(prm.shardID))
 	for i := range prm.shardID {
-		sidList[i] = prm.shardID[i].String()
+		shardIDs[i] = prm.shardID[i].String()
 	}
 
+	shards, weights, err := e.getActualShards(shardIDs, prm.handler != nil)
+	if err != nil {
+		return EvacuateShardRes{}, err
+	}
+
+	shardsToEvacuate := make(map[string]*shard.Shard)
+	for i := range shardIDs {
+		for j := range shards {
+			if shards[j].ID().String() == shardIDs[i] {
+				shardsToEvacuate[shardIDs[i]] = shards[j].Shard
+			}
+		}
+	}
+
+	e.log.Info("started shards evacuation", zap.Strings("shard_ids", shardIDs))
+
+	var res EvacuateShardRes
+
+	for _, shardID := range shardIDs {
+		if err = e.evacuateShard(shardID, prm, &res, shards, weights, shardsToEvacuate); err != nil {
+			return res, err
+		}
+	}
+
+	e.log.Info("finished shards evacuation", zap.Strings("shard_ids", shardIDs))
+	return res, nil
+}
+
+func (e *StorageEngine) evacuateShard(shardID string, prm EvacuateShardPrm, res *EvacuateShardRes,
+	shards []pooledShard, weights []float64, shardsToEvacuate map[string]*shard.Shard) error {
+	var listPrm shard.ListWithCursorPrm
+	listPrm.WithCount(defaultEvacuateBatchSize)
+
+	sh := shardsToEvacuate[shardID]
+
+	var c *meta.Cursor
+	for {
+		listPrm.WithCursor(c)
+
+		// TODO (@fyrchik): #1731 this approach doesn't work in degraded modes
+		//  because ListWithCursor works only with the metabase.
+		listRes, err := sh.ListWithCursor(listPrm)
+		if err != nil {
+			if errors.Is(err, meta.ErrEndOfListing) || errors.Is(err, shard.ErrDegradedMode) {
+				break
+			}
+			return err
+		}
+
+		if err = e.evacuateObjects(sh, listRes.AddressList(), prm, res, shards, weights, shardsToEvacuate); err != nil {
+			return err
+		}
+
+		c = listRes.Cursor()
+	}
+	return nil
+}
+
+func (e *StorageEngine) getActualShards(shardIDs []string, handlerDefined bool) ([]pooledShard, []float64, error) {
 	e.mtx.RLock()
-	for i := range sidList {
-		sh, ok := e.shards[sidList[i]]
+	defer e.mtx.RUnlock()
+
+	for i := range shardIDs {
+		sh, ok := e.shards[shardIDs[i]]
 		if !ok {
-			e.mtx.RUnlock()
-			return EvacuateShardRes{}, errShardNotFound
+			return nil, nil, errShardNotFound
 		}
 
 		if !sh.GetMode().ReadOnly() {
-			e.mtx.RUnlock()
-			return EvacuateShardRes{}, shard.ErrMustBeReadOnly
+			return nil, nil, shard.ErrMustBeReadOnly
 		}
 	}
 
-	if len(e.shards)-len(sidList) < 1 && prm.handler == nil {
-		e.mtx.RUnlock()
-		return EvacuateShardRes{}, errMustHaveTwoShards
+	if len(e.shards)-len(shardIDs) < 1 && !handlerDefined {
+		return nil, nil, errMustHaveTwoShards
 	}
 
-	e.log.Info("started shards evacuation", zap.Strings("shard_ids", sidList))
-
 	// We must have all shards, to have correct information about their
 	// indexes in a sorted slice and set appropriate marks in the metabase.
 	// Evacuated shard is skipped during put.
@@ -96,51 +151,19 @@ func (e *StorageEngine) Evacuate(prm EvacuateShardPrm) (EvacuateShardRes, error)
 			pool:        e.shardPools[id],
 		})
 	}
-	e.mtx.RUnlock()
 
 	weights := make([]float64, 0, len(shards))
 	for i := range shards {
 		weights = append(weights, e.shardWeight(shards[i].Shard))
 	}
 
-	shardMap := make(map[string]*shard.Shard)
-	for i := range sidList {
-		for j := range shards {
-			if shards[j].ID().String() == sidList[i] {
-				shardMap[sidList[i]] = shards[j].Shard
-			}
-		}
-	}
+	return shards, weights, nil
+}
 
-	var listPrm shard.ListWithCursorPrm
-	listPrm.WithCount(defaultEvacuateBatchSize)
-
-	var res EvacuateShardRes
-
-mainLoop:
-	for n := range sidList {
-		sh := shardMap[sidList[n]]
-
-		var c *meta.Cursor
-		for {
-			listPrm.WithCursor(c)
-
-			// TODO (@fyrchik): #1731 this approach doesn't work in degraded modes
-			//  because ListWithCursor works only with the metabase.
-			listRes, err := sh.ListWithCursor(listPrm)
-			if err != nil {
-				if errors.Is(err, meta.ErrEndOfListing) || errors.Is(err, shard.ErrDegradedMode) {
-					continue mainLoop
-				}
-				return res, err
-			}
-
-			// TODO (@fyrchik): #1731 parallelize the loop
-			lst := listRes.AddressList()
-
-		loop:
-			for i := range lst {
-				addr := lst[i].Address
+func (e *StorageEngine) evacuateObjects(sh *shard.Shard, toEvacuate []object.AddressWithType, prm EvacuateShardPrm, res *EvacuateShardRes,
+	shards []pooledShard, weights []float64, shardsToEvacuate map[string]*shard.Shard) error {
+	for i := range toEvacuate {
+		addr := toEvacuate[i].Address
 
 		var getPrm shard.GetPrm
 		getPrm.SetAddress(addr)
@@ -150,46 +173,47 @@ mainLoop:
 			if prm.ignoreErrors {
 				continue
 			}
-					return res, err
+			return err
 		}
 
-				hrw.SortHasherSliceByWeightValue(shards, weights, hrw.Hash([]byte(addr.EncodeToString())))
-				for j := range shards {
-					if _, ok := shardMap[shards[j].ID().String()]; ok {
+		if e.tryEvacuateObject(addr, getRes.Object(), sh, res, shards, weights, shardsToEvacuate) {
 			continue
 		}
-					putDone, exists := e.putToShard(shards[j].hashedShard, j, shards[j].pool, addr, getRes.Object())
-					if putDone || exists {
-						if putDone {
-							e.log.Debug("object is moved to another shard",
-								zap.String("from", sidList[n]),
-								zap.Stringer("to", shards[j].ID()),
-								zap.Stringer("addr", addr))
-
-							res.count++
-						}
-						continue loop
-					}
-				}
 
 		if prm.handler == nil {
 			// Do not check ignoreErrors flag here because
 			// ignoring errors on put make this command kinda useless.
-					return res, fmt.Errorf("%w: %s", errPutShard, lst[i])
+			return fmt.Errorf("%w: %s", errPutShard, toEvacuate[i])
 		}
 
 		err = prm.handler(addr, getRes.Object())
 		if err != nil {
-					return res, err
+			return err
 		}
 		res.count++
 	}
-
-			c = listRes.Cursor()
-		}
-	}
-
-	e.log.Info("finished shards evacuation",
-		zap.Strings("shard_ids", sidList))
-	return res, nil
+	return nil
+}
+
+func (e *StorageEngine) tryEvacuateObject(addr oid.Address, object *objectSDK.Object, sh *shard.Shard, res *EvacuateShardRes,
+	shards []pooledShard, weights []float64, shardsToEvacuate map[string]*shard.Shard) bool {
+	hrw.SortHasherSliceByWeightValue(shards, weights, hrw.Hash([]byte(addr.EncodeToString())))
+	for j := range shards {
+		if _, ok := shardsToEvacuate[shards[j].ID().String()]; ok {
+			continue
+		}
+		putDone, exists := e.putToShard(shards[j].hashedShard, j, shards[j].pool, addr, object)
+		if putDone || exists {
+			if putDone {
+				e.log.Debug("object is moved to another shard",
+					zap.Stringer("from", sh.ID()),
+					zap.Stringer("to", shards[j].ID()),
+					zap.Stringer("addr", addr))
+				res.count++
+			}
+			return true
+		}
+	}
+
+	return false
 }