diff --git a/src/mito2/src/access_layer.rs b/src/mito2/src/access_layer.rs
index 163d003397..2950ae6a1c 100644
--- a/src/mito2/src/access_layer.rs
+++ b/src/mito2/src/access_layer.rs
@@ -51,6 +51,7 @@ pub struct Metrics {
     pub index_update: Duration,
     pub index_finish: Duration,
     pub close: Duration,
+    pub num_series: usize,
 }
 
 impl Metrics {
diff --git a/src/mito2/src/sst/parquet/writer.rs b/src/mito2/src/sst/parquet/writer.rs
index d6875afafe..b6a4360581 100644
--- a/src/mito2/src/sst/parquet/writer.rs
+++ b/src/mito2/src/sst/parquet/writer.rs
@@ -163,6 +163,7 @@ where
         let write_format =
             WriteFormat::new(self.metadata.clone()).with_override_sequence(override_sequence);
         let mut stats = SourceStats::default();
+        let mut last_key = None;
 
         while let Some(res) = self
             .write_next_batch(&mut source, &write_format, opts, metrics)
@@ -171,6 +172,15 @@ where
         {
             match res {
                 Ok(mut batch) => {
+                    if let Some(last) = &last_key {
+                        if last != batch.primary_key() {
+                            metrics.num_series += 1;
+                            last_key = Some(batch.primary_key().to_vec());
+                        }
+                    } else {
+                        metrics.num_series += 1;
+                    }
+
                     stats.update(&batch);
                     let index_start = Instant::now();
                     self.get_or_create_indexer().await.update(&mut batch).await;