[#1463] blobovnicza: Determine db size via `os.Stat`

Currently we use `(*bbolt.Bucket).Stats().KeyN` for estimating database
size. However, it iterates over all pages in bucket and thus heavily
depends on the bucket size. This commit replaces initial size estimation
with a single `os.Stat` call.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/local_object_storage/blobovnicza/control.go

@@ -2,6 +2,7 @@ package blobovnicza
 
 import (
 	"fmt"
+	"os"
 	"path/filepath"
 
 	"github.com/nspcc-dev/neofs-node/pkg/util"
@@ -53,8 +54,6 @@ func (b *Blobovnicza) Init() error {
 		return nil
 	}
 
-	var size uint64
-
 	err := b.boltDB.Update(func(tx *bbolt.Tx) error {
 		return b.iterateBucketKeys(func(lower, upper uint64, key []byte) (bool, error) {
 			// create size range bucket
@@ -63,18 +62,25 @@ func (b *Blobovnicza) Init() error {
 			b.log.Debug("creating bucket for size range",
 				zap.String("range", rangeStr))
 
-			buck, err := tx.CreateBucketIfNotExists(key)
+			_, err := tx.CreateBucketIfNotExists(key)
 			if err != nil {
 				return false, fmt.Errorf("(%T) could not create bucket for bounds %s: %w",
 					b, rangeStr, err)
 			}
 
-			size += uint64(buck.Stats().KeyN) * (upper + lower) / 2
 			return false, nil
 		})
 	})
+	if err != nil {
+		return err
+	}
 
-	b.filled.Store(size)
+	info, err := os.Stat(b.path)
+	if err != nil {
+		return fmt.Errorf("can't determine DB size: %w", err)
+	}
+
+	b.filled.Store(uint64(info.Size()))
 	return err
 }
 

pkg/local_object_storage/blobstor/blobovnicza_test.go

@@ -40,7 +40,11 @@ func TestBlobovniczas(t *testing.T) {
 
 	c := defaultCfg()
 
-	var width, depth, szLim uint64 = 2, 2, 2 << 10
+	var width, depth uint64 = 2, 2
+
+	// sizeLim must be big enough, to hold at least multiple pages.
+	// 32 KiB is the initial size after all by-size buckets are created.
+	var szLim uint64 = 32*1024 + 1
 
 	for _, opt := range []Option{
 		WithLogger(l),
@@ -77,7 +81,7 @@ func TestBlobovniczas(t *testing.T) {
 
 		// save object in blobovnicza
 		id, err := b.put(addr, d)
-		require.NoError(t, err)
+		require.NoError(t, err, i)
 
 		// get w/ blobovnicza ID
 		var prm GetSmallPrm