diff --git a/src/connector/src/macros.rs b/src/connector/src/macros.rs
index c0f09342ecc9..ccb3096e4304 100644
--- a/src/connector/src/macros.rs
+++ b/src/connector/src/macros.rs
@@ -270,7 +270,7 @@ macro_rules! impl_common_split_reader_logic {
                 let data_stream = self.into_data_stream();
 
                 let data_stream = data_stream
-                    .map_ok(move |data_batch| {
+                    .inspect_ok(move |data_batch| {
                         metrics
                             .partition_input_count
                             .with_label_values(&[&actor_id, &source_id, &split_id])
@@ -286,7 +286,6 @@ macro_rules! impl_common_split_reader_logic {
                             .partition_input_bytes
                             .with_label_values(&[&actor_id, &source_id, &split_id])
                             .inc_by(sum_bytes);
-                        data_batch
                     })
                     .boxed();
                 let parser =
diff --git a/src/connector/src/source/datagen/source/reader.rs b/src/connector/src/source/datagen/source/reader.rs
index 0cd54491fced..a70877164df6 100644
--- a/src/connector/src/source/datagen/source/reader.rs
+++ b/src/connector/src/source/datagen/source/reader.rs
@@ -151,8 +151,22 @@ impl SplitReader for DatagenSplitReader {
         // spawn_data_generation_stream(self.generator.into_native_stream(), BUFFER_SIZE).boxed()
         match self.parser_config.specific {
             SpecificParserConfig::Native => {
-                spawn_data_generation_stream(self.generator.into_native_stream(), BUFFER_SIZE)
-                    .boxed()
+                let actor_id = self.source_ctx.source_info.actor_id.to_string();
+                let source_id = self.source_ctx.source_info.source_id.to_string();
+                let split_id = self.split_id.to_string();
+                let metrics = self.source_ctx.metrics.clone();
+                spawn_data_generation_stream(
+                    self.generator
+                        .into_native_stream()
+                        .inspect_ok(move |chunk_with_states| {
+                            metrics
+                                .partition_input_count
+                                .with_label_values(&[&actor_id, &source_id, &split_id])
+                                .inc_by(chunk_with_states.chunk.cardinality() as u64);
+                        }),
+                    BUFFER_SIZE,
+                )
+                .boxed()
             }
             _ => self.into_chunk_stream(),
         }
diff --git a/src/connector/src/source/nexmark/source/reader.rs b/src/connector/src/source/nexmark/source/reader.rs
index 06c252b2eeda..df081acabb83 100644
--- a/src/connector/src/source/nexmark/source/reader.rs
+++ b/src/connector/src/source/nexmark/source/reader.rs
@@ -16,7 +16,7 @@ use std::time::Duration;
 
 use anyhow::Result;
 use async_trait::async_trait;
-use futures::StreamExt;
+use futures::{StreamExt, TryStreamExt};
 use futures_async_stream::try_stream;
 use maplit::hashmap;
 use nexmark::config::NexmarkConfig;
@@ -105,15 +105,30 @@ impl SplitReader for NexmarkSplitReader {
     }
 
     fn into_stream(self) -> BoxSourceWithStateStream {
+        let actor_id = self.source_ctx.source_info.actor_id.to_string();
+        let source_id = self.source_ctx.source_info.source_id.to_string();
+        let split_id = self.split_id.clone();
+        let metrics = self.source_ctx.metrics.clone();
+
         // Will buffer at most 4 event chunks.
         const BUFFER_SIZE: usize = 4;
-        spawn_data_generation_stream(self.into_chunk_stream(), BUFFER_SIZE).boxed()
+        spawn_data_generation_stream(
+            self.into_native_stream()
+                .inspect_ok(move |chunk_with_states| {
+                    metrics
+                        .partition_input_count
+                        .with_label_values(&[&actor_id, &source_id, &split_id])
+                        .inc_by(chunk_with_states.chunk.cardinality() as u64);
+                }),
+            BUFFER_SIZE,
+        )
+        .boxed()
     }
 }
 
 impl NexmarkSplitReader {
     #[try_stream(boxed, ok = StreamChunkWithState, error = RwError)]
-    async fn into_chunk_stream(mut self) {
+    async fn into_native_stream(mut self) {
         let start_time = Instant::now();
         let start_offset = self.generator.global_offset();
         let start_ts = self.generator.timestamp();