Update configuration-vocabulary.md and trace-sampling.md (#5409)

docs/en/setup/backend/configuration-vocabulary.md

@@ -133,6 +133,7 @@ core|default|role|Option values, `Mixed/Receiver/Aggregator`. **Receiver** mode
 | agent-analyzer | default | Agent Analyzer. | SW_AGENT_ANALYZER | default |
 | - | -| sampleRate|Sampling rate for receiving trace. The precision is 1/10000. 10000 means 100% sample in default.|SW_TRACE_SAMPLE_RATE|10000|
 | - | - |slowDBAccessThreshold|The slow database access thresholds. Unit ms.|SW_SLOW_DB_THRESHOLD|default:200,mongodb:100|
+| - | - |forceSampleErrorSegment|When sampling mechanism activated, this config would make the error status segment sampled, ignoring the sampling rate.|SW_FORCE_SAMPLE_ERROR_SEGMENT|true|
 | receiver-sharing-server|default| Sharing server provides new gRPC and restful servers for data collection. Ana make the servers in the core module working for internal communication only.| - | - |
 | - | - | restHost| Binding IP of restful service. Services include GraphQL query and HTTP data report| - | - |
 | - | - | restPort | Binding port of restful service |  - | - |

docs/en/setup/backend/trace-sampling.md

@@ -15,10 +15,14 @@ agent-analyzer:
   default:
     ...
     sampleRate: ${SW_TRACE_SAMPLE_RATE:1000} # The sample rate precision is 1/10000. 10000 means 100% sample in default.
+    forceSampleErrorSegment: ${SW_FORCE_SAMPLE_ERROR_SEGMENT:true} # When sampling mechanism activated, this config would make the error status segment sampled, ignoring the sampling rate.
 ```
 
-`sampleRate` is for you to set sample rate to this backend. 
-The sample rate precision is 1/10000. 10000 means 100% sample in default. 
+`sampleRate` is for you to set sample rate to this backend.
+The sample rate precision is 1/10000. 10000 means 100% sample in default.
+
+`forceSampleErrorSegment` is for you to open force save some error segment when sampling mechanism active.
+When sampling mechanism activated, this config would make the error status segment sampled, ignoring the sampling rate.
 
 # Recommendation
 You could set different backend instances with different `sampleRate` values, but we recommend you to set the same.