410 lines
14 KiB
Rust
410 lines
14 KiB
Rust
use tokio::fs::{File, OpenOptions};
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use tokio::fs;
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use std::path::Path;
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use std::marker::PhantomData;
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use std::collections::{BTreeMap, HashSet};
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use bincode;
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use bincode::{Decode, Encode};
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use crate::segments::entry::EntryDetailed;
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use crate::segments::entry_header::EntryHeader;
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use crate::segments::store_header::StoreHeader;
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use crate::store::{Store, FilePosition, Column, Result, ROWS_FILE_NAME, GARBAGE_COLLECTION_INTERMEDIATE_ROWS_FILE_NAME};
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use crate::index::Index;
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use crate::cursor_capabilities::primitive::{CursorCanRead, CursorCanWrite};
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use crate::cursor_capabilities::traversal::CursorCanTraverse;
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use crate::cursor_capabilities::entry_modification::CursorCanModifyEntries;
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use crate::cursor_capabilities::index_access::{CursorCanWriteToIndex, CursorCanReadIndex};
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const GARBAGE_COLLECTION_TRIGGER: usize = 100;
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// ===Concrete Cursors===
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pub struct ReadCursor<'a, T> {
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header: StoreHeader,
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indexes: &'a [Option<Index<T, FilePosition>>],
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file: File,
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eof_file_position: FilePosition,
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}
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pub struct WriteCursor<'a, T> {
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header: &'a mut StoreHeader,
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indexes: &'a mut [Option<Index<T, FilePosition>>],
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file: File,
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eof_file_position: FilePosition,
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}
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// This is used as a cursor to temporary file during Garbage Collection
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pub struct AppendOnlyCursor<T> {
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header: StoreHeader,
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file: File,
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data_type: PhantomData<T>,
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eof_file_position: FilePosition,
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}
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// ===========Implementations=============
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// ===primitive capabilities===
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impl <T>CursorCanRead<T> for ReadCursor<'_, T> {
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fn file(&mut self) -> &mut File {
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&mut self.file
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}
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fn eof_file_position(&self) -> FilePosition {
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self.eof_file_position
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}
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}
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impl <T>CursorCanRead<T> for WriteCursor<'_, T> {
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fn file(&mut self) -> &mut File {
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&mut self.file
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}
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fn eof_file_position(&self) -> FilePosition {
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self.eof_file_position
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}
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}
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impl <T>CursorCanRead<T> for AppendOnlyCursor<T> {
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fn file(&mut self) -> &mut File {
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&mut self.file
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}
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fn eof_file_position(&self) -> FilePosition {
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self.eof_file_position
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}
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}
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impl <T>CursorCanWrite<T> for WriteCursor<'_, T> {}
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impl <T>CursorCanWrite<T> for AppendOnlyCursor<T> {}
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// ===capability to access header===
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impl <T>CursorCanTraverse<T> for ReadCursor<'_, T> {
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fn header(&self) -> &StoreHeader { &self.header }
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}
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impl <T>CursorCanTraverse<T> for WriteCursor<'_, T> {
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fn header(&self) -> &StoreHeader { &self.header }
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}
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impl <T>CursorCanTraverse<T> for AppendOnlyCursor<T> {
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fn header(&self) -> &StoreHeader { &self.header }
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}
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impl <T>CursorCanModifyEntries<T> for WriteCursor<'_, T> {
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fn header_mut(&mut self) -> &mut StoreHeader { self.header }
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fn set_eof_file_position(&mut self, new_file_position: FilePosition) { self.eof_file_position = new_file_position }
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}
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impl <T>CursorCanModifyEntries<T> for AppendOnlyCursor<T> {
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fn header_mut(&mut self) -> &mut StoreHeader { &mut self.header }
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fn set_eof_file_position(&mut self, new_file_position: FilePosition) { self.eof_file_position = new_file_position }
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}
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// ===capability to access index===
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impl <T>CursorCanReadIndex<T> for ReadCursor<'_, T> {
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fn indexes(&mut self) -> &[Option<Index<T, FilePosition>>] { &self.indexes }
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}
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impl <T>CursorCanReadIndex<T> for WriteCursor<'_, T> {
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fn indexes(&mut self) -> &[Option<Index<T, FilePosition>>] { &self.indexes }
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}
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impl <T>CursorCanWriteToIndex<T> for WriteCursor<'_, T> {
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fn indexes_mut(&mut self) -> &mut [Option<Index<T, FilePosition>>] { self.indexes }
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}
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// ===Specifics===
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impl <'cursor, T> ReadCursor<'cursor, T> {
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pub async fn new<'store: 'cursor>(store: &'store Store<T>) -> Result<Self>
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where T: Send + Sync
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{
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let path_to_rows = Path::new(&store.header.table_folder).join(ROWS_FILE_NAME);
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let file: File =
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OpenOptions::new()
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.read(true)
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.open(path_to_rows)
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.await?;
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let mut cursor = Self {
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header: store.header.clone(),
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file,
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indexes: &store.indexes,
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eof_file_position: 0,
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};
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let eof_file_position: FilePosition = cursor.seek_to_end().await?;
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cursor.eof_file_position = eof_file_position;
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cursor.seek_to_start_of_data().await?;
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Ok(cursor)
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}
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}
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impl <'cursor, T> WriteCursor<'cursor, T>
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{
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// 'store lives atleast as long as 'cursor
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pub async fn new<'store: 'cursor>(store: &'store mut Store<T>) -> Result<Self>
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where T: Send
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{
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let path_to_rows = Path::new(&store.header.table_folder).join(ROWS_FILE_NAME);
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let file: File =
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OpenOptions::new()
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.read(true)
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.write(true)
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.open(path_to_rows)
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.await?;
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let mut cursor = Self {
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header: &mut store.header,
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file,
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indexes: &mut store.indexes,
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eof_file_position: 0,
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};
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let eof_file_position: FilePosition = cursor.seek_to_end().await?;
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cursor.eof_file_position = eof_file_position;
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cursor.seek_to_start_of_data().await?;
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Ok(cursor)
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}
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// ===Entry Header Manipulation===
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// assumes we are at the start of valid entry.
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async fn set_new_entry_header(&mut self, entry_header: EntryHeader) -> Result<()>
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where T: Send
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{
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let bytes: Vec<u8> = entry_header.encode()?;
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self.write_bytes(&bytes).await?;
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Ok(())
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}
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// ===Deletion===
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pub async fn mark_deleted_at(&mut self, file_position: FilePosition, enable_garbage_collector: bool) -> Result<()>
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where T: Encode + Decode + Ord + Send + Sync + Clone + Ord
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{
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self.seek_to(file_position).await?;
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let mut entry_header = self.read_entry_header().await?;
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if entry_header.is_deleted {
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Ok(())
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} else {
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// Update store and entry headers
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self.increment_deleted_count().await?;
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self.seek_to(file_position).await?;
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entry_header.is_deleted = true;
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self.set_new_entry_header(entry_header.into()).await?;
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// Update index
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self.seek_to(file_position).await?;
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match self.next().await? {
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Some(entry) => {
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self.delete_entry_values_from_indexes(entry).await?
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},
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None => {
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// SAFETY: We just modified its header, so it must exist.
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unreachable!()
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}
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}
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if enable_garbage_collector {
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self.attempt_garbage_collection_if_necessary().await?;
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}
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Ok(())
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}
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}
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async fn find_first_eq_bruteforce_and_delete(&mut self, column: Column, t0: &T, enable_garbage_collector: bool) -> Result<Option<EntryDetailed<T>>>
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where T: Encode + Decode + Ord + Send + Sync + Clone
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{
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let maybe_entry = self.find_first_eq_bruteforce(column, t0).await?;
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if let Some(entry) = maybe_entry {
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self.mark_deleted_at(entry.file_position, enable_garbage_collector).await?;
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Ok(Some(entry))
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} else {
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Ok(maybe_entry)
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}
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}
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// Doesn't update indexes.
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async fn find_all_eq_bruteforce_and_delete(&mut self, column: Column, t0: &T) -> Result<usize>
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where T: Encode + Decode + Ord + Send + Sync + Clone
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{
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let mut count = 0;
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while let Some(_) = self.find_first_eq_bruteforce_and_delete(column, t0, false).await? {
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count += 1;
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}
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Ok(count)
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}
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pub async fn delete_all_entries(&mut self, enable_garbage_collector: bool) -> Result<usize>
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where T: Encode + Decode + Ord + Send + Sync + Clone
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{
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let mut count = 0;
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while let Some(entry) = self.next_alive().await? {
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count += 1;
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self.mark_deleted_at(entry.file_position, false).await?
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}
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if enable_garbage_collector {
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self.attempt_garbage_collection_if_necessary().await?;
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}
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Ok(count)
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}
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pub async fn delete_entries_where_eq(&mut self, column: Column, value: &T, enable_garbage_collector: bool) -> Result<usize>
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where T: Encode + Decode + Ord + Send + Sync + Clone
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{
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let count =
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if self.header().is_column_indexed(column) {
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let entries = self.index_lookup(column, value).await?;
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let count = entries.len();
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for entry in entries {
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self.mark_deleted_at(entry.file_position, false).await?
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}
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count
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} else {
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let count = self.find_all_eq_bruteforce_and_delete(column, value).await?;
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count
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};
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if enable_garbage_collector {
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self.attempt_garbage_collection_if_necessary().await?;
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}
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Ok(count)
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}
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// ===Indexing===
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// WARNING: Assumes the column is NOT indexable.
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pub async fn attach_index(&mut self, column: Column) -> Result<()>
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where T: Ord + Decode + Encode + Send + Sync
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{
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// New Index
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let index = Store::create_empty_index_at(&self.header, column).await?;
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self.indexes[column as usize] = Some(index);
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// Mark column as indexed
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self.header.make_column_indexed(column);
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self.set_header(&self.header.clone()).await?;
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// Build index
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self.seek_to_start_of_data().await?;
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while let Some((_, file_position, value)) = self.next_alive_at_column(column).await? {
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self.insert_into_index(column, value, file_position).await?
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}
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Ok(())
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}
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// ===Garbage Collection===
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async fn attempt_garbage_collection_if_necessary(&mut self) -> Result<()>
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where T: Send + Sync + Decode + Encode + Clone + Ord
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{
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if self.header.deleted_count > GARBAGE_COLLECTION_TRIGGER {
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println!("=======START GARBAGE COLLECTOR====");
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self.initiate_garbage_collection().await?;
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println!("=======GARBAGE COLLECTOR FINISHED====");
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}
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Ok(())
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}
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pub async fn initiate_garbage_collection(&mut self) -> Result<usize>
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where T: Send + Sync + Decode + Encode + Clone + Ord
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{
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let mut cursor_to_intermediate = self.spawn_cursor_to_intermediate_file().await?;
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// Since garbage collection changes FilePositions of live entries, we need to update the
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// indexes too.
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let mut in_memory_indexes: Vec<Option<BTreeMap<T, HashSet<FilePosition>>>> = Vec::with_capacity(self.header.number_of_columns);
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for column in 0..self.header.number_of_columns {
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if self.header.is_column_indexed(column as Column) {
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let in_memory_index = BTreeMap::new();
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in_memory_indexes.push(Some(in_memory_index))
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} else {
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in_memory_indexes.push(None)
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}
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}
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// We'll dump all alive entries into a new file.
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let mut entries_deleted = 0;
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self.seek_to_start_of_data().await?;
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{
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while let Some(live_entry) = self.next_alive().await? {
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entries_deleted += 1;
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let file_position = cursor_to_intermediate.append_entry_no_indexing(&live_entry.forget()).await?;
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// Update index. (Wouldn't it be nice if we had `for let ...`?)
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for (maybe_in_memory_index, value) in in_memory_indexes.iter_mut().zip(&live_entry.data) {
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if let Some(in_memory_index) = maybe_in_memory_index {
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in_memory_index.entry(value.clone()).or_insert_with(HashSet::new).insert(file_position);
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}
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}
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}
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}
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// ===swap===
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// swapping indexes
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// Update indexes on disk.
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for (column, maybe_in_memory_index) in in_memory_indexes.into_iter().enumerate() {
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if let Some(in_memory_index) = maybe_in_memory_index {
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let index = self.mut_index_at(column as Column);
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index.reset(in_memory_index).await?;
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}
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}
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// swapping headers
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self.header.deleted_count = 0;
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self.header.total_count = cursor_to_intermediate.header.total_count;
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self.file = cursor_to_intermediate.file;
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self.eof_file_position = cursor_to_intermediate.eof_file_position;
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// swap files on disk
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// current file
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let path_to_table = Path::new(&self.header.table_folder);
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let path_to_rows = path_to_table.join(ROWS_FILE_NAME);
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let path_to_intermediate_rows = path_to_table.join(GARBAGE_COLLECTION_INTERMEDIATE_ROWS_FILE_NAME);
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fs::remove_file(path_to_rows.clone()).await?;
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fs::rename(path_to_intermediate_rows, path_to_rows).await?;
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Ok(entries_deleted)
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}
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async fn spawn_cursor_to_intermediate_file(&self) -> Result<AppendOnlyCursor<T>>
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where T: Send
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{
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let table_folder = self.header.table_folder.clone();
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let path_to_table = Path::new(&table_folder);
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let path_to_rows = path_to_table.join(GARBAGE_COLLECTION_INTERMEDIATE_ROWS_FILE_NAME);
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let intermediate_file: File = Store::<T>::create_empty_rows_file(path_to_rows, &self.header).await?;
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let intermediate_header: StoreHeader = StoreHeader {
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table_folder,
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number_of_columns: self.header.number_of_columns,
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deleted_count: 0,
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total_count: 0,
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primary_column: self.header.primary_column,
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indexed_columns: self.header.indexed_columns.clone(),
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};
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// Creates a new (append) cursor to the intermediate file in which we'll dump the live entries.
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let mut cursor_to_intermediate = AppendOnlyCursor {
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header: intermediate_header,
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file: intermediate_file,
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data_type: PhantomData::<T>,
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eof_file_position: 0,
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};
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let eof_file_position: FilePosition = cursor_to_intermediate.seek_to_end().await?;
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cursor_to_intermediate.eof_file_position = eof_file_position;
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Ok(cursor_to_intermediate)
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}
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}
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