checkin initial MVCC codebase

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm-mvcc/src/manifest.rs

@@ -0,0 +1,74 @@
+use std::fs::{File, OpenOptions};
+use std::io::{Read, Write};
+use std::path::Path;
+use std::sync::Arc;
+
+use anyhow::{Context, Result};
+use parking_lot::{Mutex, MutexGuard};
+use serde::{Deserialize, Serialize};
+use serde_json::Deserializer;
+
+use crate::compact::CompactionTask;
+
+pub struct Manifest {
+    file: Arc<Mutex<File>>,
+}
+
+#[derive(Serialize, Deserialize)]
+pub enum ManifestRecord {
+    Flush(usize),
+    NewMemtable(usize),
+    Compaction(CompactionTask, Vec<usize>),
+}
+
+impl Manifest {
+    pub fn create(path: impl AsRef<Path>) -> Result<Self> {
+        Ok(Self {
+            file: Arc::new(Mutex::new(
+                OpenOptions::new()
+                    .read(true)
+                    .create_new(true)
+                    .write(true)
+                    .open(path)
+                    .context("failed to create manifest")?,
+            )),
+        })
+    }
+
+    pub fn recover(path: impl AsRef<Path>) -> Result<(Self, Vec<ManifestRecord>)> {
+        let mut file = OpenOptions::new()
+            .read(true)
+            .append(true)
+            .open(path)
+            .context("failed to recover manifest")?;
+        let mut buf = Vec::new();
+        file.read_to_end(&mut buf)?;
+        let stream = Deserializer::from_slice(&buf).into_iter::<ManifestRecord>();
+        let mut records = Vec::new();
+        for x in stream {
+            records.push(x?);
+        }
+        Ok((
+            Self {
+                file: Arc::new(Mutex::new(file)),
+            },
+            records,
+        ))
+    }
+
+    pub fn add_record(
+        &self,
+        _state_lock_observer: &MutexGuard<()>,
+        record: ManifestRecord,
+    ) -> Result<()> {
+        self.add_record_when_init(record)
+    }
+
+    pub fn add_record_when_init(&self, record: ManifestRecord) -> Result<()> {
+        let mut file = self.file.lock();
+        let buf = serde_json::to_vec(&record)?;
+        file.write_all(&buf)?;
+        file.sync_all()?;
+        Ok(())
+    }
+}