eth/api_debug: comment of SetTrieFlushInterval

Signed-off-by: jsvisa <delweng@gmail.com>

eth/api_debug.go

@@ -395,6 +395,9 @@ func (api *DebugAPI) GetAccessibleState(from, to rpc.BlockNumber) (uint64, error
 
 // SetTrieFlushInterval configures how often in-memory tries are persisted
 // to disk. The value is in terms of block processing time, not wall clock.
+// If the value is shorter than the block generation time, or even 0 or negative,
+// the node will flush trie after processing each block.
+// Its behavior is the same as that of an archive node, so please use it with caution.
 func (api *DebugAPI) SetTrieFlushInterval(interval string) error {
 	t, err := time.ParseDuration(interval)
 	if err != nil {
@@ -406,6 +409,5 @@ func (api *DebugAPI) SetTrieFlushInterval(interval string) error {
 
 // GetTrieFlushInterval gets the current value of in-memroy tries flush interval
 func (api *DebugAPI) GetTrieFlushInterval() string {
-	interval := api.eth.blockchain.GetTrieFlushInterval()
-	return interval.String()
+	return api.eth.blockchain.GetTrieFlushInterval().String()
 }