diff --git a/quickwit/quickwit-common/src/metrics.rs b/quickwit/quickwit-common/src/metrics.rs
index 7eed30ef197..db303b1b763 100644
--- a/quickwit/quickwit-common/src/metrics.rs
+++ b/quickwit/quickwit-common/src/metrics.rs
@@ -18,6 +18,7 @@
 // along with this program. If not, see <http://www.gnu.org/licenses/>.
 
 use std::collections::HashMap;
+use std::sync::OnceLock;
 
 use once_cell::sync::Lazy;
 use prometheus::{Encoder, HistogramOpts, Opts, TextEncoder};
@@ -259,10 +260,10 @@ pub struct InFlightDataGauges {
     pub wal: IntGauge,
     pub fetch_stream: IntGauge,
     pub multi_fetch_stream: IntGauge,
-    pub sources: InFlightDataSourceGauges,
     pub doc_processor_mailbox: IntGauge,
     pub indexer_mailbox: IntGauge,
     pub index_writer: IntGauge,
+    in_flight_gauge_vec: IntGaugeVec<1>,
 }
 
 impl Default for InFlightDataGauges {
@@ -282,37 +283,70 @@ impl Default for InFlightDataGauges {
             wal: in_flight_gauge_vec.with_label_values(["wal"]),
             fetch_stream: in_flight_gauge_vec.with_label_values(["fetch_stream"]),
             multi_fetch_stream: in_flight_gauge_vec.with_label_values(["multi_fetch_stream"]),
-            sources: InFlightDataSourceGauges::new(&in_flight_gauge_vec),
             doc_processor_mailbox: in_flight_gauge_vec.with_label_values(["doc_processor_mailbox"]),
             indexer_mailbox: in_flight_gauge_vec.with_label_values(["indexer_mailbox"]),
             index_writer: in_flight_gauge_vec.with_label_values(["index_writer"]),
+            in_flight_gauge_vec: in_flight_gauge_vec.clone(),
         }
     }
 }
 
-/// TODO make those lazy.
-#[derive(Clone)]
-pub struct InFlightDataSourceGauges {
-    pub file: IntGauge,
-    pub ingest: IntGauge,
-    pub kafka: IntGauge,
-    pub kinesis: IntGauge,
-    pub pubsub: IntGauge,
-    pub pulsar: IntGauge,
-    pub other: IntGauge,
-}
+impl InFlightDataGauges {
+    #[inline]
+    pub fn file(&self) -> &IntGauge {
+        static GAUGE: OnceLock<IntGauge> = OnceLock::new();
+        GAUGE.get_or_init(|| self.in_flight_gauge_vec.with_label_values(["file_source"]))
+    }
 
-impl InFlightDataSourceGauges {
-    pub fn new(in_flight_gauge_vec: &IntGaugeVec<1>) -> Self {
-        Self {
-            file: in_flight_gauge_vec.with_label_values(["file_source"]),
-            ingest: in_flight_gauge_vec.with_label_values(["ingest_source"]),
-            kafka: in_flight_gauge_vec.with_label_values(["kafka_source"]),
-            kinesis: in_flight_gauge_vec.with_label_values(["kinesis_source"]),
-            pubsub: in_flight_gauge_vec.with_label_values(["pubsub_source"]),
-            pulsar: in_flight_gauge_vec.with_label_values(["pulsar_source"]),
-            other: in_flight_gauge_vec.with_label_values(["other"]),
-        }
+    #[inline]
+    pub fn ingest(&self) -> &IntGauge {
+        static GAUGE: OnceLock<IntGauge> = OnceLock::new();
+        GAUGE.get_or_init(|| {
+            self.in_flight_gauge_vec
+                .with_label_values(["ingest_source"])
+        })
+    }
+
+    #[inline]
+    pub fn kafka(&self) -> &IntGauge {
+        static GAUGE: OnceLock<IntGauge> = OnceLock::new();
+        GAUGE.get_or_init(|| self.in_flight_gauge_vec.with_label_values(["kafka_source"]))
+    }
+
+    #[inline]
+    pub fn kinesis(&self) -> &IntGauge {
+        static GAUGE: OnceLock<IntGauge> = OnceLock::new();
+        GAUGE.get_or_init(|| {
+            self.in_flight_gauge_vec
+                .with_label_values(["kinesis_source"])
+        })
+    }
+
+    #[inline]
+    pub fn pubsub(&self) -> &IntGauge {
+        static GAUGE: OnceLock<IntGauge> = OnceLock::new();
+        GAUGE.get_or_init(|| {
+            self.in_flight_gauge_vec
+                .with_label_values(["pubsub_source"])
+        })
+    }
+
+    #[inline]
+    pub fn pulsar(&self) -> &IntGauge {
+        static GAUGE: OnceLock<IntGauge> = OnceLock::new();
+        GAUGE.get_or_init(|| {
+            self.in_flight_gauge_vec
+                .with_label_values(["pulsar_source"])
+        })
+    }
+
+    #[inline]
+    pub fn other(&self) -> &IntGauge {
+        static GAUGE: OnceLock<IntGauge> = OnceLock::new();
+        GAUGE.get_or_init(|| {
+            self.in_flight_gauge_vec
+                .with_label_values(["pulsar_source"])
+        })
     }
 }
 
diff --git a/quickwit/quickwit-indexing/src/source/mod.rs b/quickwit/quickwit-indexing/src/source/mod.rs
index 21d23774bd2..ed01d8041af 100644
--- a/quickwit/quickwit-indexing/src/source/mod.rs
+++ b/quickwit/quickwit-indexing/src/source/mod.rs
@@ -492,13 +492,13 @@ impl BatchBuilder {
 
     pub fn with_capacity(capacity: usize, source_type: SourceType) -> Self {
         let gauge = match source_type {
-            SourceType::File => &MEMORY_METRICS.in_flight.sources.file,
-            SourceType::IngestV2 => &MEMORY_METRICS.in_flight.sources.ingest,
-            SourceType::Kafka => &MEMORY_METRICS.in_flight.sources.kafka,
-            SourceType::Kinesis => &MEMORY_METRICS.in_flight.sources.kinesis,
-            SourceType::PubSub => &MEMORY_METRICS.in_flight.sources.pubsub,
-            SourceType::Pulsar => &MEMORY_METRICS.in_flight.sources.pulsar,
-            _ => &MEMORY_METRICS.in_flight.sources.other,
+            SourceType::File => MEMORY_METRICS.in_flight.file(),
+            SourceType::IngestV2 => MEMORY_METRICS.in_flight.ingest(),
+            SourceType::Kafka => MEMORY_METRICS.in_flight.kafka(),
+            SourceType::Kinesis => MEMORY_METRICS.in_flight.kinesis(),
+            SourceType::PubSub => MEMORY_METRICS.in_flight.pubsub(),
+            SourceType::Pulsar => MEMORY_METRICS.in_flight.pulsar(),
+            _ => MEMORY_METRICS.in_flight.other(),
         };
         let gauge_guard = GaugeGuard::from_gauge(gauge);