diff --git a/quickwit/quickwit-common/src/metrics.rs b/quickwit/quickwit-common/src/metrics.rs
index 97664f70d0a..4e256dd1e6f 100644
--- a/quickwit/quickwit-common/src/metrics.rs
+++ b/quickwit/quickwit-common/src/metrics.rs
@@ -252,12 +252,13 @@ impl Default for MemoryMetrics {
 
 #[derive(Clone)]
 pub struct InFlightDataGauges {
-    pub doc_processor_mailbox: IntGauge,
-    pub index_writer: IntGauge,
-    pub indexer_mailbox: IntGauge,
-    pub ingest_router: IntGauge,
     pub rest_server: IntGauge,
+    pub ingest_router: IntGauge,
+    pub wal: IntGauge,
     pub sources: InFlightDataSourceGauges,
+    pub doc_processor_mailbox: IntGauge,
+    pub indexer_mailbox: IntGauge,
+    pub index_writer: IntGauge,
 }
 
 impl Default for InFlightDataGauges {
@@ -270,12 +271,13 @@ impl Default for InFlightDataGauges {
             ["component"],
         );
         Self {
-            doc_processor_mailbox: in_flight_gauge_vec.with_label_values(["doc_processor_mailbox"]),
-            index_writer: in_flight_gauge_vec.with_label_values(["index_writer"]),
-            indexer_mailbox: in_flight_gauge_vec.with_label_values(["indexer_mailbox"]),
-            ingest_router: in_flight_gauge_vec.with_label_values(["ingest_router"]),
             rest_server: in_flight_gauge_vec.with_label_values(["rest_server"]),
+            ingest_router: in_flight_gauge_vec.with_label_values(["ingest_router"]),
+            wal: in_flight_gauge_vec.with_label_values(["wal"]),
             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"]),
         }
     }
 }
diff --git a/quickwit/quickwit-indexing/src/actors/indexer.rs b/quickwit/quickwit-indexing/src/actors/indexer.rs
index e827e4d0380..f4f4418d773 100644
--- a/quickwit/quickwit-indexing/src/actors/indexer.rs
+++ b/quickwit/quickwit-indexing/src/actors/indexer.rs
@@ -225,6 +225,10 @@ impl IndexerState {
         let publish_lock = self.publish_lock.clone();
         let publish_token_opt = self.publish_token_opt.clone();
 
+        let mut split_builders_guard =
+            GaugeGuard::from_gauge(&crate::metrics::INDEXER_METRICS.split_builders);
+        split_builders_guard.add(1);
+
         let workbench = IndexingWorkbench {
             workbench_id,
             create_instant: Instant::now(),
@@ -242,6 +246,7 @@ impl IndexerState {
                     .in_flight_data
                     .index_writer,
             ),
+            split_builders_guard,
         };
         Ok(workbench)
     }
@@ -364,6 +369,7 @@ struct IndexingWorkbench {
     last_delete_opstamp: u64,
     // Number of bytes declared as used by tantivy.
     memory_usage: GaugeGuard,
+    split_builders_guard: GaugeGuard,
 }
 
 pub struct Indexer {
@@ -635,6 +641,7 @@ impl Indexer {
             batch_parent_span,
             indexing_permit,
             memory_usage,
+            split_builders_guard,
             ..
         }) = self.indexing_workbench_opt.take()
         else {
@@ -687,6 +694,7 @@ impl Indexer {
                 commit_trigger,
                 batch_parent_span,
                 memory_usage,
+                _split_builders_guard: split_builders_guard,
             },
         )
         .await?;
diff --git a/quickwit/quickwit-indexing/src/metrics.rs b/quickwit/quickwit-indexing/src/metrics.rs
index 56eb300f66d..583a103f966 100644
--- a/quickwit/quickwit-indexing/src/metrics.rs
+++ b/quickwit/quickwit-indexing/src/metrics.rs
@@ -27,6 +27,7 @@ pub struct IndexerMetrics {
     pub processed_bytes: IntCounterVec<2>,
     pub backpressure_micros: IntCounterVec<1>,
     pub available_concurrent_upload_permits: IntGaugeVec<1>,
+    pub split_builders: IntGauge,
     pub ongoing_merge_operations: IntGauge,
     pub pending_merge_operations: IntGauge,
     pub pending_merge_bytes: IntGauge,
@@ -66,6 +67,12 @@ impl Default for IndexerMetrics {
                 &[],
                 ["component"],
             ),
+            split_builders: new_gauge(
+                "split_builders",
+                "Number of existing index writer instances.",
+                "indexing",
+                &[],
+            ),
             ongoing_merge_operations: new_gauge(
                 "ongoing_merge_operations",
                 "Number of ongoing merge operations",
diff --git a/quickwit/quickwit-indexing/src/models/indexed_split.rs b/quickwit/quickwit-indexing/src/models/indexed_split.rs
index 0fd90aa4855..0dff364c6f3 100644
--- a/quickwit/quickwit-indexing/src/models/indexed_split.rs
+++ b/quickwit/quickwit-indexing/src/models/indexed_split.rs
@@ -185,6 +185,7 @@ pub struct IndexedSplitBatchBuilder {
     pub commit_trigger: CommitTrigger,
     pub batch_parent_span: Span,
     pub memory_usage: GaugeGuard,
+    pub _split_builders_guard: GaugeGuard,
 }
 
 /// Sends notifications to the Publisher that the last batch of splits was emtpy.
diff --git a/quickwit/quickwit-ingest/src/ingest_v2/metrics.rs b/quickwit/quickwit-ingest/src/ingest_v2/metrics.rs
index 8f84c1acc03..4dfcaa72fd5 100644
--- a/quickwit/quickwit-ingest/src/ingest_v2/metrics.rs
+++ b/quickwit/quickwit-ingest/src/ingest_v2/metrics.rs
@@ -31,7 +31,6 @@ pub(super) struct IngestV2Metrics {
     pub wal_acquire_lock_requests_in_flight: IntGaugeVec<2>,
     pub wal_acquire_lock_request_duration_secs: HistogramVec<2>,
     pub wal_disk_used_bytes: IntGauge,
-    pub wal_memory_allocated_bytes: IntGauge,
     pub wal_memory_used_bytes: IntGauge,
 }
 
@@ -77,12 +76,6 @@ impl Default for IngestV2Metrics {
                 "ingest",
                 &[],
             ),
-            wal_memory_allocated_bytes: new_gauge(
-                "wal_memory_allocated_bytes",
-                "WAL memory allocated in bytes.",
-                "ingest",
-                &[],
-            ),
             wal_memory_used_bytes: new_gauge(
                 "wal_memory_used_bytes",
                 "WAL memory used in bytes.",
@@ -97,8 +90,9 @@ pub(super) fn report_wal_usage(wal_usage: ResourceUsage) {
     INGEST_V2_METRICS
         .wal_disk_used_bytes
         .set(wal_usage.disk_used_bytes as i64);
-    INGEST_V2_METRICS
-        .wal_memory_allocated_bytes
+    quickwit_common::metrics::MEMORY_METRICS
+        .in_flight_data
+        .wal
         .set(wal_usage.memory_allocated_bytes as i64);
     INGEST_V2_METRICS
         .wal_memory_used_bytes