Remove unnecessary reader seeks

src/csv.rs

@@ -6,6 +6,7 @@ use std::cmp::max;
 use std::fs::File;
 use std::sync::{Arc, Mutex};
 use std::thread::{self, JoinHandle};
+use std::time;
 
 fn string_record_to_vec(record: &csv::StringRecord) -> Vec<String> {
     let mut string_vec = Vec::new();
@@ -174,7 +175,11 @@ impl CsvLensReader {
         let pos = Position::new();
         self.reader.seek(pos)?;
 
+        let tic = time::Instant::now();
         let pos_table = self.get_pos_table();
+        stats.pos_table_elapsed = Some(tic.elapsed());
+        stats.pos_table_entry = pos_table.len();
+
         let mut pos_iter = pos_table.iter();
         let mut indices_iter = indices.iter();
 
@@ -189,15 +194,19 @@ impl CsvLensReader {
             }
             // seek as close to the next wanted record index as possible
             let index = next_wanted.unwrap();
+            let mut seek_pos: Option<Position> = None;
             while let Some(pos) = next_pos {
                 if self.config.position_to_record_index(pos.record()) <= index.record_index {
-                    self.reader.seek(pos.clone())?;
-                    stats.log_seek();
+                    seek_pos.replace(pos.clone());
                 } else {
                     break;
                 }
                 next_pos = pos_iter.next();
             }
+            if let Some(pos) = seek_pos {
+                self.reader.seek(pos)?;
+                stats.log_seek();
+            }
 
             // note that records() excludes header by default, but here the first entry is header
             // because of the seek() above.
@@ -289,13 +298,17 @@ impl CsvLensReader {
 pub struct GetRowsStats {
     pub num_seek: u64,
     pub num_parsed_record: u64,
+    pub pos_table_elapsed: Option<time::Duration>,
+    pub pos_table_entry: usize,
 }
 
 impl GetRowsStats {
     fn new() -> GetRowsStats {
         GetRowsStats {
             num_seek: 0,
             num_parsed_record: 0,
+            pos_table_elapsed: None,
+            pos_table_entry: 0,
         }
     }
 
@@ -467,7 +480,7 @@ mod tests {
         let mut r = CsvLensReader::new(config).unwrap();
         r.wait_internal();
         let indices = vec![1, 3, 5, 1234, 2345, 3456, 4999];
-        let (rows, stats) = r.get_rows_impl(&indices).unwrap();
+        let (rows, mut stats) = r.get_rows_impl(&indices).unwrap();
         let expected = vec![
             Row::new(2, vec!["A2", "B2"]),
             Row::new(4, vec!["A4", "B4"]),
@@ -478,9 +491,12 @@ mod tests {
             Row::new(5000, vec!["A5000", "B5000"]),
         ];
         assert_eq!(rows, expected);
+        stats.pos_table_elapsed.take();
         let expected = GetRowsStats {
-            num_seek: 115,
+            num_seek: 4,
             num_parsed_record: 218,
+            pos_table_elapsed: None,
+            pos_table_entry: 115,
         };
         assert_eq!(stats, expected);
     }
@@ -491,12 +507,15 @@ mod tests {
         let mut r = CsvLensReader::new(config).unwrap();
         r.wait_internal();
         let indices = vec![1234];
-        let (rows, stats) = r.get_rows_impl(&indices).unwrap();
+        let (rows, mut stats) = r.get_rows_impl(&indices).unwrap();
         let expected = vec![Row::new(1235, vec!["A1235", "B1235"])];
         assert_eq!(rows, expected);
+        stats.pos_table_elapsed.take();
         let expected = GetRowsStats {
-            num_seek: 25,
+            num_seek: 1,
             num_parsed_record: 8,
+            pos_table_elapsed: None,
+            pos_table_entry: 115,
         };
         assert_eq!(stats, expected);
     }
@@ -507,12 +526,15 @@ mod tests {
         let mut r = CsvLensReader::new(config).unwrap();
         r.wait_internal();
         let indices = vec![2];
-        let (rows, stats) = r.get_rows_impl(&indices).unwrap();
+        let (rows, mut stats) = r.get_rows_impl(&indices).unwrap();
         let expected = vec![Row::new(3, vec!["A3", "B3"])];
         assert_eq!(rows, expected);
+        stats.pos_table_elapsed.take();
         let expected = GetRowsStats {
             num_seek: 0,
             num_parsed_record: 4, // 3 + 1 (including header)
+            pos_table_elapsed: None,
+            pos_table_entry: 115,
         };
         assert_eq!(stats, expected);
     }

src/ui.rs

@@ -990,8 +990,15 @@ impl DebugStats {
         let mut line = "[".to_string();
         if let Some(stats) = &self.rows_view_stats {
             line += format!(
-                "rows:{:.3}ms seek:{} parse:{}",
+                "rows:{:.3}ms pos:{}us npos:{} seek:{} parse:{}",
                 stats.elapsed.as_micros() as f64 / 1000.0,
+                stats
+                    .reader_stats
+                    .pos_table_elapsed
+                    .as_ref()
+                    .map(|e| e.as_micros())
+                    .unwrap_or(0),
+                stats.reader_stats.pos_table_entry,
                 stats.reader_stats.num_seek,
                 stats.reader_stats.num_parsed_record
             )