bugfix: set default max_result_limit for search to 256*1024 (#6525)

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## main / unreleased
 
+* [CHANGE] Set default `max_result_limit` for search to 256*1024 [#6525](https://github.com/grafana/tempo/pull/6525) (@zhxiaogg)
 * [CHANGE] **BREAKING CHANGE** Remove Opencensus receiver [#6523](https://github.com/grafana/tempo/pull/6523) (@javiermolinar)
 * [CHANGE] Upgrade Tempo to Go 1.26.0 [#6443](https://github.com/grafana/tempo/pull/6443) (@stoewer)
 * [CHANGE] Allow duplicate dimensions for span metrics and service graphs. This is a valid use case if using different instrumentation libraries, with spans having "deployment.environment" and others "deployment_environment", for example. [#6288](https://github.com/grafana/tempo/pull/6288) (@carles-grafana)

docs/sources/tempo/configuration/manifest.md

@@ -397,7 +397,7 @@ query_frontend:
         concurrent_jobs: 1000
         target_bytes_per_job: 104857600
         default_result_limit: 20
-        max_result_limit: 0
+        max_result_limit: 262144
         max_duration: 168h0m0s
         query_backend_after: 15m0s
         ingester_shards: 3

modules/frontend/config.go

@@ -94,7 +94,7 @@ func (cfg *Config) RegisterFlagsAndApplyDefaults(string, *flag.FlagSet) {
 		Sharder: SearchSharderConfig{
 			QueryBackendAfter:      15 * time.Minute,
 			DefaultLimit:           20,
-			MaxLimit:               0,
+			MaxLimit:               256 * 1024,
 			MaxDuration:            168 * time.Hour, // 1 week
 			ConcurrentRequests:     defaultConcurrentRequests,
 			TargetBytesPerRequest:  defaultTargetBytesPerRequest,

modules/frontend/config_test.go

@@ -0,0 +1,15 @@
+package frontend
+
+import (
+	"flag"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSearchSharderConfigDefaults(t *testing.T) {
+	cfg := &Config{}
+	cfg.RegisterFlagsAndApplyDefaults("", &flag.FlagSet{})
+
+	assert.Equal(t, uint32(256*1024), cfg.Search.Sharder.MaxLimit)
+}