add a threshold for search if want to emit a metric

in case some bad regex search defined,
it would be easier to identify the offender

README.rst

@@ -279,6 +279,7 @@ Example configuration for a single reader::
           "pattern": "SENSITIVE",
           "replacement": "[REDACTED]"
         }],
+      "threshold_for_metric_emit": 10
       "tags": {
           "type": "container"
       }
@@ -375,7 +376,9 @@ Using backrefs, the message can also be restructured into a new format.
 Change this setting to true to emit metrics to the metrics host whenever a secret pattern is matched.
 This matching happens before other filtering to help catch secrets being leaked to disk.
 
-
+``threshold_for_metric_emit`` ( default: ``10``)
+For the regex searches in journalpump, if search takes longer than this value, default 10 seconds, a metric will be emitted.
+type: int unit: second
 
 Sender Configuration
 --------------------

journalpump/journalpump.py

@@ -158,6 +158,7 @@ def __init__(
         self.secret_filter_metrics = self._configure_secret_filter_metrics(config)
         self.secret_filter_metric_last_send = time.monotonic()
         self._is_ready = True
+        self.threshold_for_metric_emit = self._configure_threshold_for_metric_emit(config)
 
     def invalidate(self) -> None:
         """
@@ -551,6 +552,18 @@ def _validate_and_build_secret_filters(self, config):
 
         return secret_filters
 
+    def _configure_threshold_for_metric_emit(self, config):
+        threshold_for_metric_emit = config.get("threshold_for_metric_emit")
+        if threshold_for_metric_emit is not None:
+            try:
+                threshold = int(threshold_for_metric_emit)
+            except ValueError:
+                raise ValueError("Invalid value for threshold_for_metric_emit. Must be an integer.")
+        else:
+            # Use a default value if the "threshold_for_metric_emit" is not present
+            threshold = int(10)
+        return threshold
+
     def perform_searches(self, jobject):
         entry = jobject.entry
         results = {}
@@ -580,7 +593,16 @@ def perform_searches(self, jobject):
                             break
                         byte_fields[field] = line
 
+                start_time = time.perf_counter()
                 match = regex.search(line)
+                regex_search_duration = time.perf_counter() - start_time
+                if regex_search_duration > self.threshold_for_metric_emit:
+                    self.stats.gauge(
+                        metric="journal.perform_search_regex_duration",
+                        value=regex_search_duration,
+                        tags=self.make_tags({"regex": regex.pattern}),
+                    )
+                    self.log.info("Slow regex search: %s for duration %s seconds", regex, regex_search_duration)
                 if not match:
                     all_match = False
                     break