db read with mmap

Cargo.lock

@@ -174,6 +174,7 @@ dependencies = [
  "ledb",
  "ledb-derive",
  "ledb-types",
+ "memmap",
  "rand",
  "serde",
  "serde_derive",
@@ -638,6 +639,16 @@ version = "2.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2dffe52ecf27772e601905b7522cb4ef790d2cc203488bbd0e2fe85fcb74566d"
 
+[[package]]
+name = "memmap"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6585fd95e7bb50d6cc31e20d4cf9afb4e2ba16c5846fc76793f11218da9c475b"
+dependencies = [
+ "libc",
+ "winapi",
+]
+
 [[package]]
 name = "memoffset"
 version = "0.6.5"

Cargo.toml

@@ -22,6 +22,7 @@ rand="0.8"
 clap = { version = "3.2.22", features = ["derive"] }
 bincode = "^2.0.0-rc.2"
 zstd = "^0.10"
+memmap = "0.7.0"
 
 [dev-dependencies]
 criterion = "0.4.0"

bench.txt

@@ -6,18 +6,18 @@
 hyperfine  -n print -n print2 -n zip-print -w 100 -m 100 ".\target\release\chgk_ledb.exe print 444" ".\target\release\chgk_ledb.exe print2 444" ".\target\release\chgk_ledb.exe zip-print 4 84"
 
 Benchmark 1: print
-  Time (mean ± σ):      20.0 ms ±   1.5 ms    [User: 3.4 ms, System: 11.7 ms]
-  Range (min … max):    17.4 ms …  24.1 ms    100 runs
+  Time (mean ± σ):      20.0 ms ±   1.7 ms    [User: 5.8 ms, System: 12.3 ms]
+  Range (min … max):    18.0 ms …  30.9 ms    100 runs
 
 Benchmark 2: print2
-  Time (mean ± σ):      19.4 ms ±   1.5 ms    [User: 5.5 ms, System: 9.8 ms]
-  Range (min … max):    17.0 ms …  23.9 ms    100 runs
+  Time (mean ± σ):      19.1 ms ±   1.2 ms    [User: 5.7 ms, System: 12.3 ms]
+  Range (min … max):    17.2 ms …  22.1 ms    100 runs
 
 Benchmark 3: zip-print
-  Time (mean ± σ):      40.2 ms ±   2.3 ms    [User: 15.1 ms, System: 18.9 ms]
-  Range (min … max):    36.6 ms …  48.1 ms    100 runs
+  Time (mean ± σ):      41.1 ms ±   1.4 ms    [User: 16.1 ms, System: 22.2 ms]
+  Range (min … max):    38.9 ms …  45.4 ms    100 runs
 
 Summary
   'print2' ran
-    1.03 ± 0.11 times faster than 'print'
-    2.07 ± 0.20 times faster than 'zip-print'
+    1.05 ± 0.11 times faster than 'print'
+    2.16 ± 0.15 times faster than 'zip-print'

benches/db_bench.rs

@@ -3,7 +3,7 @@ extern crate criterion;
 
 #[path = "../src/db.rs"]
 mod db;
-use std::{path::PathBuf};
+use std::path::PathBuf;
 
 use db::{Reader, Writer, WriterOpts};
 
@@ -88,6 +88,5 @@ fn config() -> Criterion {
     Criterion::default().sample_size(40)
 }
 
-
 criterion_group! {name=benches; config = config(); targets = db_read, db_write}
 criterion_main!(benches);

src/db.rs

@@ -1,10 +1,12 @@
 use std::{
     fs,
-    io::{self, Cursor, Read, Seek, Write},
+    io::{self, Cursor, Read, Write},
     marker::PhantomData,
     path::Path,
 };
 
+use memmap::{Mmap, MmapOptions};
+
 type LSize = u32;
 const LEN_SIZE: usize = std::mem::size_of::<LSize>();
 const BINCODE_CFG: bincode::config::Configuration = bincode::config::standard();
@@ -152,7 +154,7 @@ pub struct Reader<T>
 where
     T: bincode::Decode,
 {
-    input: io::BufReader<fs::File>,
+    mmap: Mmap,
     count: usize,
     first_pos: LSize,
     _t: PhantomData<*const T>,
@@ -162,19 +164,18 @@ impl<T> Reader<T>
 where
     T: bincode::Decode,
 {
-    pub fn new<P: AsRef<Path>>(path: P, buf_size: usize) -> Result<Self, String> {
-        let input = fs::File::open(path).str_err()?;
-        let mut input = io::BufReader::with_capacity(buf_size, input);
+    pub fn new<P: AsRef<Path>>(path: P, _buf_size: usize) -> Result<Self, String> {
+        let file = fs::File::open(path).str_err()?;
+        let mmap = unsafe { MmapOptions::new().map(&file).str_err()? };
 
         // read first pos and records count
-        let mut first_data: [u8; LEN_SIZE] = [0; LEN_SIZE];
-        input.read_exact(&mut first_data).str_err()?;
+        let first_data: [u8; LEN_SIZE] = mmap[0..LEN_SIZE].try_into().str_err()?;
         let first_pos = LSize::from_le_bytes(first_data);
         let tab_len = (first_pos as usize) / LEN_SIZE;
         let count = tab_len - 1;
 
         Ok(Self {
-            input,
+            mmap,
             count,
             first_pos,
             _t: PhantomData,
@@ -194,30 +195,24 @@ where
         let data_pos = if 0 == index {
             self.first_pos
         } else {
-            let tab_pos: u64 = (index * LEN_SIZE).try_into().str_err()?;
-            let mut pos_curr_data: [u8; LEN_SIZE] = [0; LEN_SIZE];
-            let cur_pos = self.input.stream_position().str_err()? as i64;
-            self.input
-                .seek_relative((tab_pos as i64) - cur_pos)
+            let tab_pos: usize = index * LEN_SIZE;
+            let pos_curr_data: [u8; LEN_SIZE] = self.mmap[tab_pos..(tab_pos + LEN_SIZE)]
+                .try_into()
                 .str_err()?;
-
-            self.input.read_exact(&mut pos_curr_data).str_err()?;
             LSize::from_le_bytes(pos_curr_data)
-        };
+        } as usize;
 
         // read next item pos
-        let mut pos_next_data: [u8; LEN_SIZE] = [0; LEN_SIZE];
-        self.input.read_exact(&mut pos_next_data).str_err()?;
-        let data_pos_next = LSize::from_le_bytes(pos_next_data);
+        let next_pos: usize = (index + 1) * LEN_SIZE;
+        let pos_next_data: [u8; LEN_SIZE] = self.mmap[next_pos..(next_pos + LEN_SIZE)]
+            .try_into()
+            .str_err()?;
+        let data_pos_next = LSize::from_le_bytes(pos_next_data) as usize;
         // calc item data length
         let data_len = data_pos_next - data_pos;
 
         // read & unpack item data
-        let cur_pos = self.input.stream_position().str_err()? as i64;
-        self.input
-            .seek_relative((data_pos as i64) - cur_pos)
-            .str_err()?;
-        let reader = self.input.by_ref().take(data_len as u64);
+        let reader = self.mmap[data_pos..data_pos_next].take(data_len as u64);
         let data = zstd::decode_all(reader).str_err()?;
 
         // decode item