chore: print series count after wal replay (#6344)

* chore/print-series-count-after-wal-replay:
 ### Add Series Count Functionality and Logging Enhancements

 - **`time_partition.rs`**: Introduced `series_count` method to calculate the total timeseries count across all time partitions.
 - **`opener.rs`**: Enhanced logging to include the total timeseries replayed during WAL replay.
 - **`version.rs`**: Added `series_count` method to `VersionControlData` for approximating timeseries count in the current version.
 - **`handler.rs`**: Added entry and exit logging for the `sql` function to trace execution flow.

Signed-off-by: Lei, HUANG <mrsatangel@gmail.com>

* chore/print-series-count-after-wal-replay:
 ### Remove Unused Import

 - **File Modified**: `src/servers/src/http/handler.rs`
 - **Change Summary**: Removed the unused `info` import from `common_telemetry`.

Signed-off-by: Lei, HUANG <mrsatangel@gmail.com>

---------

Signed-off-by: Lei, HUANG <mrsatangel@gmail.com>

src/mito2/src/memtable/time_partition.rs

@@ -656,6 +656,11 @@ impl TimePartitions {
 
         Ok(())
     }
+
+    /// Timeseries count in all time partitions.
+    pub(crate) fn series_count(&self) -> usize {
+        self.inner.lock().unwrap().series_count()
+    }
 }
 
 /// Computes the start timestamp of the partition for `ts`.
@@ -697,6 +702,13 @@ impl PartitionsInner {
         self.next_memtable_id += 1;
         id
     }
+
+    pub(crate) fn series_count(&self) -> usize {
+        self.parts
+            .iter()
+            .map(|p| p.memtable.stats().series_count)
+            .sum()
+    }
 }
 
 /// Time range of a partition.

src/mito2/src/region/opener.rs

@@ -665,9 +665,10 @@ where
     // to avoid reading potentially incomplete entries in the future.
     (on_region_opened)(region_id, flushed_entry_id, provider).await?;
 
+    let series_count = version_control.current().series_count();
     info!(
-        "Replay WAL for region: {}, rows recovered: {}, last entry id: {}",
-        region_id, rows_replayed, last_entry_id
+        "Replay WAL for region: {}, rows recovered: {}, last entry id: {}, total timeseries replayed: {}",
+        region_id, rows_replayed, last_entry_id, series_count
     );
     Ok(last_entry_id)
 }

src/mito2/src/region/version.rs

@@ -249,6 +249,13 @@ pub(crate) struct VersionControlData {
     pub(crate) is_dropped: bool,
 }
 
+impl VersionControlData {
+    /// Approximate timeseries count in current version.
+    pub(crate) fn series_count(&self) -> usize {
+        self.version.memtables.mutable.series_count()
+    }
+}
+
 /// Static metadata of a region.
 #[derive(Clone, Debug)]
 pub(crate) struct Version {