diff --git a/Cargo.lock b/Cargo.lock
index da7ff9461400..3c320e4c78ac 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -7036,6 +7036,7 @@ dependencies = [
  "datatypes",
  "futures",
  "greptime-proto",
+ "metrics",
  "promql-parser",
  "prost",
  "query",
diff --git a/src/mito2/src/metrics.rs b/src/mito2/src/metrics.rs
index faa73f659c0a..4b32ec877e43 100644
--- a/src/mito2/src/metrics.rs
+++ b/src/mito2/src/metrics.rs
@@ -45,6 +45,8 @@ pub const WRITE_STALL_TOTAL: &str = "mito.write.stall_total";
 pub const WRITE_REJECT_TOTAL: &str = "mito.write.reject_total";
 /// Elapsed time of each write stage.
 pub const WRITE_STAGE_ELAPSED: &str = "mito.write.stage_elapsed";
+/// Counter of rows to write.
+pub const WRITE_ROWS_TOTAL: &str = "mito.write.rows_total";
 // ------ End of write related metrics
 
 // Compaction metrics
diff --git a/src/mito2/src/region_write_ctx.rs b/src/mito2/src/region_write_ctx.rs
index 8e83a6442a1f..5270ceec326d 100644
--- a/src/mito2/src/region_write_ctx.rs
+++ b/src/mito2/src/region_write_ctx.rs
@@ -15,7 +15,7 @@
 use std::mem;
 use std::sync::Arc;
 
-use api::v1::{Mutation, Rows, WalEntry};
+use api::v1::{Mutation, OpType, Rows, WalEntry};
 use common_query::Output;
 use snafu::ResultExt;
 use store_api::logstore::LogStore;
@@ -92,6 +92,14 @@ pub(crate) struct RegionWriteCtx {
     ///
     /// The i-th notify is for i-th mutation.
     notifiers: Vec<WriteNotify>,
+    /// The write operation is failed and we should not write to the mutable memtable.
+    failed: bool,
+
+    // Metrics:
+    /// Rows to put.
+    pub(crate) put_num: usize,
+    /// Rows to delete.
+    pub(crate) delete_num: usize,
 }
 
 impl RegionWriteCtx {
@@ -112,6 +120,9 @@ impl RegionWriteCtx {
             next_entry_id: last_entry_id + 1,
             wal_entry: WalEntry::default(),
             notifiers: Vec::new(),
+            failed: false,
+            put_num: 0,
+            delete_num: 0,
         }
     }
 
@@ -130,6 +141,13 @@ impl RegionWriteCtx {
 
         // Increase sequence number.
         self.next_sequence += num_rows as u64;
+
+        // Update metrics.
+        match OpType::from_i32(op_type) {
+            Some(OpType::Delete) => self.delete_num += num_rows,
+            Some(OpType::Put) => self.put_num += num_rows,
+            None => (),
+        }
     }
 
     /// Encode and add WAL entry to the writer.
@@ -153,6 +171,9 @@ impl RegionWriteCtx {
         for notify in &mut self.notifiers {
             notify.err = Some(err.clone());
         }
+
+        // Fail the whole write operation.
+        self.failed = true;
     }
 
     /// Updates next entry id.
@@ -164,6 +185,10 @@ impl RegionWriteCtx {
     pub(crate) fn write_memtable(&mut self) {
         debug_assert_eq!(self.notifiers.len(), self.wal_entry.mutations.len());
 
+        if self.failed {
+            return;
+        }
+
         let mutable = &self.version.memtables.mutable;
         // Takes mutations from the wal entry.
         let mutations = mem::take(&mut self.wal_entry.mutations);
diff --git a/src/mito2/src/worker/handle_write.rs b/src/mito2/src/worker/handle_write.rs
index de6b6a5c5ea0..873ef726fb99 100644
--- a/src/mito2/src/worker/handle_write.rs
+++ b/src/mito2/src/worker/handle_write.rs
@@ -24,7 +24,10 @@ use store_api::metadata::RegionMetadata;
 use store_api::storage::RegionId;
 
 use crate::error::{RejectWriteSnafu, Result};
-use crate::metrics::{STAGE_LABEL, WRITE_REJECT_TOTAL, WRITE_STAGE_ELAPSED, WRITE_STALL_TOTAL};
+use crate::metrics::{
+    STAGE_LABEL, TYPE_LABEL, WRITE_REJECT_TOTAL, WRITE_ROWS_TOTAL, WRITE_STAGE_ELAPSED,
+    WRITE_STALL_TOTAL,
+};
 use crate::region_write_ctx::RegionWriteCtx;
 use crate::request::{SenderWriteRequest, WriteRequest};
 use crate::worker::RegionWorkerLoop;
@@ -80,13 +83,19 @@ impl<S: LogStore> RegionWorkerLoop<S> {
             }
         }
 
+        let (mut put_rows, mut delete_rows) = (0, 0);
         // Write to memtables.
         {
             let _timer = timer!(WRITE_STAGE_ELAPSED, &[(STAGE_LABEL, "write_memtable")]);
             for mut region_ctx in region_ctxs.into_values() {
                 region_ctx.write_memtable();
+                put_rows += region_ctx.put_num;
+                delete_rows += region_ctx.delete_num;
             }
         }
+
+        counter!(WRITE_ROWS_TOTAL, put_rows as u64, TYPE_LABEL => "put");
+        counter!(WRITE_ROWS_TOTAL, delete_rows as u64, TYPE_LABEL => "delete");
     }
 }
 
diff --git a/src/promql/Cargo.toml b/src/promql/Cargo.toml
index 00f55ce296c5..990197a34c4b 100644
--- a/src/promql/Cargo.toml
+++ b/src/promql/Cargo.toml
@@ -17,6 +17,7 @@ datafusion.workspace = true
 datatypes = { workspace = true }
 futures = "0.3"
 greptime-proto.workspace = true
+metrics = { workspace = true }
 promql-parser = "0.1.1"
 prost.workspace = true
 session = { workspace = true }
diff --git a/src/promql/src/extension_plan/series_divide.rs b/src/promql/src/extension_plan/series_divide.rs
index 3487fe578678..fdf2c9cdf9bc 100644
--- a/src/promql/src/extension_plan/series_divide.rs
+++ b/src/promql/src/extension_plan/series_divide.rs
@@ -38,6 +38,7 @@ use prost::Message;
 use snafu::ResultExt;
 
 use crate::error::{DeserializeSnafu, Result};
+use crate::metrics::PROMQL_SERIES_COUNT;
 
 #[derive(Debug, PartialEq, Eq, Hash)]
 pub struct SeriesDivide {
@@ -204,6 +205,7 @@ impl ExecutionPlan for SeriesDivideExec {
             schema,
             input,
             metric: baseline_metric,
+            num_series: 0,
         }))
     }
 
@@ -239,6 +241,7 @@ pub struct SeriesDivideStream {
     schema: SchemaRef,
     input: SendableRecordBatchStream,
     metric: BaselineMetrics,
+    num_series: usize,
 }
 
 impl RecordBatchStream for SeriesDivideStream {
@@ -259,6 +262,7 @@ impl Stream for SeriesDivideStream {
                         Some(Ok(batch)) => batch,
                         None => {
                             self.buffer = None;
+                            self.num_series += 1;
                             return Poll::Ready(Some(Ok(batch)));
                         }
                         error => return Poll::Ready(error),
@@ -271,12 +275,16 @@ impl Stream for SeriesDivideStream {
                     let result_batch = batch.slice(0, same_length);
                     let remaining_batch = batch.slice(same_length, batch.num_rows() - same_length);
                     self.buffer = Some(remaining_batch);
+                    self.num_series += 1;
                     return Poll::Ready(Some(Ok(result_batch)));
                 }
             } else {
                 let batch = match ready!(self.as_mut().fetch_next_batch(cx)) {
                     Some(Ok(batch)) => batch,
-                    None => return Poll::Ready(None),
+                    None => {
+                        metrics::histogram!(PROMQL_SERIES_COUNT, self.num_series as f64);
+                        return Poll::Ready(None);
+                    }
                     error => return Poll::Ready(error),
                 };
                 self.buffer = Some(batch);
diff --git a/src/promql/src/lib.rs b/src/promql/src/lib.rs
index 1f636dcb5394..9514a015380b 100644
--- a/src/promql/src/lib.rs
+++ b/src/promql/src/lib.rs
@@ -18,5 +18,6 @@
 pub mod error;
 pub mod extension_plan;
 pub mod functions;
+mod metrics;
 pub mod planner;
 pub mod range_array;
diff --git a/src/promql/src/metrics.rs b/src/promql/src/metrics.rs
new file mode 100644
index 000000000000..b8bebf7a43f3
--- /dev/null
+++ b/src/promql/src/metrics.rs
@@ -0,0 +1,16 @@
+// Copyright 2023 Greptime Team
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/// Counter for the number of series processed per query.
+pub static PROMQL_SERIES_COUNT: &str = "promql.series_count";
diff --git a/src/query/src/dist_plan/merge_scan.rs b/src/query/src/dist_plan/merge_scan.rs
index ce07b9e5dde2..cc06f84d82f0 100644
--- a/src/query/src/dist_plan/merge_scan.rs
+++ b/src/query/src/dist_plan/merge_scan.rs
@@ -14,6 +14,7 @@
 
 use std::any::Any;
 use std::sync::Arc;
+use std::time::Duration;
 
 use arrow_schema::{Schema as ArrowSchema, SchemaRef as ArrowSchemaRef};
 use async_stream::stream;
@@ -39,8 +40,12 @@ use futures_util::StreamExt;
 use greptime_proto::v1::region::{QueryRequest, RegionRequestHeader};
 use snafu::ResultExt;
 use store_api::storage::RegionId;
+use tokio::time::Instant;
 
 use crate::error::ConvertSchemaSnafu;
+use crate::metrics::{
+    METRIC_MERGE_SCAN_ERRORS_TOTAL, METRIC_MERGE_SCAN_POLL_ELAPSED, METRIC_MERGE_SCAN_REGIONS,
+};
 use crate::region_query::RegionQueryHandlerRef;
 
 #[derive(Debug, Hash, PartialEq, Eq, Clone)]
@@ -161,6 +166,7 @@ impl MergeScanExec {
         let trace_id = trace_id().unwrap_or_default();
 
         let stream = Box::pin(stream!({
+            metrics::histogram!(METRIC_MERGE_SCAN_REGIONS, regions.len() as f64);
             let _finish_timer = metric.finish_time().timer();
             let mut ready_timer = metric.ready_time().timer();
             let mut first_consume_timer = Some(metric.first_consume_time().timer());
@@ -178,12 +184,21 @@ impl MergeScanExec {
                 let mut stream = region_query_handler
                     .do_get(request)
                     .await
-                    .map_err(BoxedError::new)
+                    .map_err(|e| {
+                        metrics::increment_counter!(METRIC_MERGE_SCAN_ERRORS_TOTAL);
+                        BoxedError::new(e)
+                    })
                     .context(ExternalSnafu)?;
 
                 ready_timer.stop();
 
+                let mut poll_duration = Duration::new(0, 0);
+
+                let mut poll_timer = Instant::now();
                 while let Some(batch) = stream.next().await {
+                    let poll_elapsed = poll_timer.elapsed();
+                    poll_duration += poll_elapsed;
+
                     let batch = batch?;
                     // reconstruct batch using `self.schema`
                     // to remove metadata and correct column name
@@ -193,7 +208,10 @@ impl MergeScanExec {
                         first_consume_timer.stop();
                     }
                     yield Ok(batch);
+                    // reset poll timer
+                    poll_timer = Instant::now();
                 }
+                metrics::histogram!(METRIC_MERGE_SCAN_POLL_ELAPSED, poll_duration.as_secs_f64());
             }
         }));
 
diff --git a/src/query/src/metrics.rs b/src/query/src/metrics.rs
index 489e7fb62a56..7efac4e4141b 100644
--- a/src/query/src/metrics.rs
+++ b/src/query/src/metrics.rs
@@ -18,3 +18,6 @@ pub static METRIC_OPTIMIZE_LOGICAL_ELAPSED: &str = "query.optimize_logicalplan_e
 pub static METRIC_OPTIMIZE_PHYSICAL_ELAPSED: &str = "query.optimize_physicalplan_elapsed";
 pub static METRIC_CREATE_PHYSICAL_ELAPSED: &str = "query.create_physicalplan_elapsed";
 pub static METRIC_EXEC_PLAN_ELAPSED: &str = "query.execute_plan_elapsed";
+pub static METRIC_MERGE_SCAN_POLL_ELAPSED: &str = "query.merge_scan.poll_elapsed";
+pub static METRIC_MERGE_SCAN_REGIONS: &str = "query.merge_scan.regions";
+pub static METRIC_MERGE_SCAN_ERRORS_TOTAL: &str = "query.merge_scan.errors_total";
diff --git a/src/store-api/src/region_request.rs b/src/store-api/src/region_request.rs
index 9d608f2077da..04251b81aeed 100644
--- a/src/store-api/src/region_request.rs
+++ b/src/store-api/src/region_request.rs
@@ -30,7 +30,6 @@ use crate::storage::{ColumnId, RegionId, ScanRequest};
 
 #[derive(Debug, IntoStaticStr)]
 pub enum RegionRequest {
-    // TODO: rename to InsertRequest
     Put(RegionPutRequest),
     Delete(RegionDeleteRequest),
     Create(RegionCreateRequest),