Prepare for garbage collection

storage_engine/src/storage_engine.rs

@@ -1,7 +1,7 @@
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 use tokio::fs::{File, OpenOptions, DirBuilder};
 use tokio::fs;
-use std::path::Path;
+use std::path::{Path, PathBuf};
 use std::marker::PhantomData;
 use async_trait::async_trait;
 
@@ -28,7 +28,6 @@ pub struct Store<T> {
     //     {write: 0, read: n + 1} ~> {write:0, read: n} // destroy read
     //     {write: 0, read: 0} ~> {write: 1, read: 0} // create write
     //     {write: 1, read: 0} ~> {write: 0, read: 0} // destroy write
-    pub table_folder: String,
     // primary_index: Vec<Index<T, FilePosition>>>,
     // indexes: Vec<Option<Index<T, HashSet<FilePosition>>>>,
     // primary_index: Index<PositionOfValue, PositionOfRow>,
@@ -63,6 +62,7 @@ impl <T>SomethingSupportingLeq for Store<T>
 }
 
 pub const ROWS_FILE_NAME: &'static str = "rows";
+pub const GARBAGE_COLLECTION_INTERMEDIATE_ROWS_FILE_NAME: &'static str = "rows_intermediate";
 
 impl <T>Store<T> {
     // ===Creation===
@@ -72,6 +72,31 @@ impl <T>Store<T> {
         DirBuilder::new()
             .create(path_to_table).await?;
 
+        let header = StoreHeader {
+            table_folder: table_folder.to_string(),
+            number_of_columns,
+            deleted_count: 0,
+            total_count: 0,
+            primary_column,
+        };
+
+        // We don't need the file right now. Only cursors will later open it.
+        Self::create_empty_rows_file(path_to_rows, &header).await?;
+
+        // TODO: indexes
+        // let index: Index<PositionOfValue, PositionOfRow> = Index::new(
+        //     &format!("rows_{}", primary_column.to_string()),
+        // ).await?;
+
+        let store = Self {
+            header,
+            data_type: PhantomData::<T>,
+        };
+
+        Ok(store)
+    }
+
+    pub async fn create_empty_rows_file(path_to_rows: PathBuf, header: &StoreHeader) -> Result<File> {
         let mut file: File =
             OpenOptions::new()
                 .write(true)
@@ -80,28 +105,10 @@ impl <T>Store<T> {
                 .open(path_to_rows)
                 .await?;
 
-        let header = StoreHeader {
-            number_of_columns,
-            deleted_count: 0,
-            total_count: 0,
-            primary_column,
-        };
         let encoded_header: Vec<u8> = header.encode()?;
         file.write(&encoded_header).await?;
-        
 
-        // TODO: indexes
-        // let index: Index<PositionOfValue, PositionOfRow> = Index::new(
-        //     &format!("rows_{}", primary_column.to_string()),
-        // ).await?;
-
-        let store = Self {
-            table_folder: table_folder.to_string(),
-            header,
-            data_type: PhantomData::<T>,
-        };
-
-        Ok(store)
+        Ok(file)
     }
 
     pub async fn connect(table_folder: &str) -> Result<Self> 
@@ -121,10 +128,9 @@ impl <T>Store<T> {
         // header.
         let mut header_bytes = StoreHeader::decode_buffer();
         file.read_exact(&mut header_bytes).await?;
-        let header = StoreHeader::decode(&mut header_bytes).await?;
+        let header = StoreHeader::decode(table_folder, &mut header_bytes).await?;
 
         let store = Self {
-            table_folder: table_folder.to_string(),
             header,
             data_type: PhantomData::<T>,
         };