Moved work duration to a constant

blockstore/splitstore/splitstore_compact.go

@@ -66,8 +66,9 @@ var (
 )
 
 const (
-	batchSize  = 16384
-	cidKeySize = 128
+	batchSize              = 16384
+	cidKeySize             = 128
+	purgeWorkSliceDuration = time.Second
 )
 
 func (s *SplitStore) HeadChange(_, apply []*types.TipSet) error {
@@ -1381,8 +1382,8 @@ func (s *SplitStore) purge(coldr *ColdSetReader, checkpoint *Checkpoint, markSet
 			// requires write access to txnLk that may starve other operations that require
 			// access to the blockstore.
 			elapsed := time.Since(now)
-			if elapsed > time.Second {
-				// work 1 second, sleep 4, or 20% utilization
+			if elapsed > purgeWorkSliceDuration {
+				// work 1 slice, sleep 4 slices, or 20% utilization
 				time.Sleep(4 * elapsed)
 				now = time.Now()
 			}