save span with minmum latency us

docs/cn/rpcz.md

@@ -13,6 +13,7 @@
 | rpcz_database_dir | ./rpc_data/rpcz | For storing requests/contexts collected by rpcz. | src/baidu/rpc/span.cpp |
 | rpcz_keep_span_db | false | Don't remove DB of rpcz at program's exit | src/baidu/rpc/span.cpp |
 | rpcz_keep_span_seconds (R) | 3600 | Keep spans for at most so many seconds | src/baidu/rpc/span.cpp |
+| rpcz_save_span_min_latency_us (R) | 0 (default:0) | The minimum latency microseconds of span saved | src/baidu/rpc/span.cpp |
 
 若启动时未加-enable_rpcz，则可在启动后访问SERVER_URL/rpcz/enable动态开启rpcz，访问SERVER_URL/rpcz/disable则关闭，这两个链接等价于访问SERVER_URL/flags/enable_rpcz?setvalue=true和SERVER_URL/flags/enable_rpcz?setvalue=false。在r31010之后，rpc在html版本中增加了一个按钮可视化地开启和关闭。
 

src/brpc/span.cpp

@@ -59,6 +59,9 @@ BRPC_VALIDATE_GFLAG(rpcz_keep_span_seconds, PositiveInteger);
 
 DEFINE_bool(rpcz_keep_span_db, false, "Don't remove DB of rpcz at program's exit");
 
+DEFINE_int64(rpcz_save_span_min_latency_us, 0, "The minimum latency microseconds of span saved");
+BRPC_VALIDATE_GFLAG(rpcz_save_span_min_latency_us, NonNegativeInteger);
+
 struct IdGen {
  bool init;
  uint16_t seq;
@@ -574,6 +577,11 @@ leveldb::Status SpanDB::Index(const Span* span, std::string* value_buf) {
  // of time window.
 
  const int64_t start_time = span->GetStartRealTimeUs();
+ const int64_t latency_us = span->GetEndRealTimeUs() - start_time;
+ // if latency_us < FLAGS_rpcz_save_span_min_latency_us, don't save this span
+ if (latency_us < FLAGS_rpcz_save_span_min_latency_us) {
+ return leveldb::Status::OK();
+ }
  BriefSpan brief;
  brief.set_trace_id(span->trace_id());
  brief.set_span_id(span->span_id());
@@ -583,7 +591,7 @@ leveldb::Status SpanDB::Index(const Span* span, std::string* value_buf) {
  brief.set_request_size(span->request_size());
  brief.set_response_size(span->response_size());
  brief.set_start_real_us(start_time);
- brief.set_latency_us(span->GetEndRealTimeUs() - start_time);
+ brief.set_latency_us(latency_us);
  brief.set_full_method_name(span->full_method_name());
  if (!brief.SerializeToString(value_buf)) {
  return leveldb::Status::InvalidArgument(