add simple leveled compaction

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

mini-lsm/src/compact/simple_leveled.rs

@@ -0,0 +1,100 @@
+use std::collections::HashMap;
+
+use crate::lsm_storage::LsmStorageInner;
+
+pub struct SimpleLeveledCompactionOptions {
+    pub size_ratio_percent: usize,
+    pub level0_file_num_compaction_trigger: usize,
+    pub max_levels: usize,
+}
+
+pub struct SimpleLeveledCompactionTask {
+    // if upper_level is `None`, then it is L0 compaction
+    pub upper_level: Option<usize>,
+    pub upper_level_sst_ids: Vec<usize>,
+    pub lower_level: usize,
+    pub lower_level_sst_ids: Vec<usize>,
+}
+
+pub struct SimpleLeveledCompactionController {
+    options: SimpleLeveledCompactionOptions,
+}
+
+impl SimpleLeveledCompactionController {
+    pub fn new(options: SimpleLeveledCompactionOptions) -> Self {
+        Self { options }
+    }
+
+    pub fn generate_compaction_task(
+        &mut self,
+        snapshot: &LsmStorageInner,
+    ) -> Option<SimpleLeveledCompactionTask> {
+        let mut level_sizes = Vec::new();
+        level_sizes.push(snapshot.l0_sstables.len());
+        for (_, files) in &snapshot.levels {
+            level_sizes.push(files.len());
+        }
+
+        for i in 0..self.options.max_levels {
+            if i == 0
+                && snapshot.l0_sstables.len() < self.options.level0_file_num_compaction_trigger
+            {
+                continue;
+            }
+
+            let lower_level = i + 1;
+            let size_ratio = level_sizes[lower_level] as f64 / level_sizes[i] as f64;
+            if size_ratio < self.options.size_ratio_percent as f64 / 100.0 {
+                println!(
+                    "compaction triggered at level {} and {} with size ratio {}",
+                    i, lower_level, size_ratio
+                );
+                return Some(SimpleLeveledCompactionTask {
+                    upper_level: if i == 0 { None } else { Some(i) },
+                    upper_level_sst_ids: if i == 0 {
+                        snapshot.l0_sstables.clone()
+                    } else {
+                        snapshot.levels[i - 1].1.clone()
+                    },
+                    lower_level,
+                    lower_level_sst_ids: snapshot.levels[lower_level - 1].1.clone(),
+                });
+            }
+        }
+        None
+    }
+
+    pub fn apply_compaction_result(
+        &self,
+        snapshot: &LsmStorageInner,
+        task: &SimpleLeveledCompactionTask,
+        output: &[usize],
+    ) -> (LsmStorageInner, Vec<usize>) {
+        let mut snapshot = snapshot.clone();
+        let mut files_to_remove = Vec::new();
+        if let Some(upper_level) = task.upper_level {
+            assert_eq!(
+                task.upper_level_sst_ids,
+                snapshot.levels[upper_level - 1].1,
+                "sst mismatched"
+            );
+            files_to_remove.extend(&snapshot.levels[upper_level - 1].1);
+            snapshot.levels[upper_level - 1].1.clear();
+        } else {
+            assert_eq!(
+                task.upper_level_sst_ids, snapshot.l0_sstables,
+                "sst mismatched"
+            );
+            files_to_remove.extend(&snapshot.l0_sstables);
+            snapshot.l0_sstables.clear();
+        }
+        assert_eq!(
+            task.lower_level_sst_ids,
+            snapshot.levels[task.lower_level - 1].1,
+            "sst mismatched"
+        );
+        files_to_remove.extend(&snapshot.levels[task.lower_level - 1].1);
+        snapshot.levels[task.lower_level - 1].1 = output.to_vec();
+        (snapshot, files_to_remove)
+    }
+}