mvcc: Printing etcd backend database related metrics inside scheduleCompaction function

Backporting commit 21bbc82 in etcd 3.5
To improve traceability of backend database usage, Added below parameter
related to backend database usage metrics inside scheduledCompaction
function.
current-db-size-bytes
current-db-size
current-db-size-in-use-bytes
current-db-size-in-use

Signed-off-by: Rahul More <rahulbapumore@gmail.com>

server/mvcc/kvstore_compaction.go

@@ -20,6 +20,7 @@ import (
 	"time"
 
 	"go.etcd.io/etcd/server/v3/mvcc/buckets"
+	humanize "github.com/dustin/go-humanize"
 	"go.uber.org/zap"
 )
 
@@ -63,11 +64,16 @@ func (s *store) scheduleCompaction(compactMainRev, prevCompactRev int64) (KeyVal
 			tx.UnsafePut(buckets.Meta, finishedCompactKeyName, rbytes)
 			tx.Unlock()
 			hash := h.Hash()
+			size, sizeInUse := s.b.Size(), s.b.SizeInUse()
 			s.lg.Info(
 				"finished scheduled compaction",
 				zap.Int64("compact-revision", compactMainRev),
 				zap.Duration("took", time.Since(totalStart)),
 				zap.Uint32("hash", hash.Hash),
+				zap.Int64("current-db-size-bytes", size),
+				zap.String("current-db-size", humanize.Bytes(uint64(size))),
+				zap.Int64("current-db-size-in-use-bytes", sizeInUse),
+				zap.String("current-db-size-in-use", humanize.Bytes(uint64(sizeInUse))),
 			)
 			return hash, nil
 		}