481 lines
16 KiB
Rust
481 lines
16 KiB
Rust
use tokio::io::{AsyncReadExt, AsyncWriteExt, AsyncSeekExt, SeekFrom};
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use tokio::fs::{File, OpenOptions};
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use std::path::Path;
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use std::marker::PhantomData;
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use crate::error::{Error, DecodeErrorKind};
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use async_trait::async_trait;
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use bincode;
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use bincode::{Decode, Encode};
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use crate::binary_coding::{encode, decode};
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use crate::entry::{Entry, EntryDetailed};
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use crate::entry_header::{EntryHeaderWithDataSize, EntryHeader};
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use crate::store_header::StoreHeader;
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use crate::storage_engine::{Store, FilePosition, Column, Result, ROWS_FILE_NAME, GARBAGE_COLLECTION_INTERMEDIATE_ROWS_FILE_NAME};
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// ===Concrete Cursors===
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pub struct ReadCursor<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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pub struct WriteCursor<'a, T> {
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header: &'a mut 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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// ===Traits===
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#[async_trait]
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// TODO: Make this private
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pub trait PrimitiveCursor<T> {
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fn file(&mut self) -> &mut File;
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fn eof_file_position(&self) -> FilePosition;
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async fn read_bytes(&mut self, bytes: &mut [u8]) -> Result<()> {
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self.file().read_exact(bytes).await?;
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Ok(())
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}
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async fn get_bytes(&mut self, count: usize) -> Result<Vec<u8>> {
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let mut result: Vec<u8> = Vec::with_capacity(count);
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self.read_bytes(&mut result).await?;
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Ok(result)
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}
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async fn seek_to(&mut self, file_position: FilePosition) -> Result<FilePosition> {
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let file_position = self.file().seek(SeekFrom::Start(file_position)).await?;
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Ok(file_position)
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}
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// Start of the file i.e. the Header, not the entries.
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async fn seek_to_start(&mut self) -> Result<FilePosition> {
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let file_position = self.file().seek(SeekFrom::Start(0)).await?;
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Ok(file_position)
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}
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async fn seek_to_end(&mut self) -> Result<FilePosition> {
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let file_position = self.file().seek(SeekFrom::End(0)).await?;
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Ok(file_position)
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}
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async fn seek_to_start_of_data(&mut self) -> Result<FilePosition> {
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self.seek_to(StoreHeader::SIZE as u64).await
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}
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// Seeks from current position by offset and returns new file position
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async fn seek_by(&mut self, offset: i64) -> Result<FilePosition> {
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let file_position = self.file().seek(SeekFrom::Current(offset)).await?;
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Ok(file_position)
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}
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async fn current_file_position(&mut self) -> Result<FilePosition> {
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let next_file_position: FilePosition = self.file().stream_position().await?;
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Ok(next_file_position)
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}
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async fn is_at_eof(&mut self) -> Result<bool> {
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let current_file_position = self.current_file_position().await?;
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let eof_file_position = self.eof_file_position();
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Ok(current_file_position == eof_file_position)
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}
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}
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#[async_trait]
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pub trait CursorWithStoreHeader<T>: PrimitiveCursor<T> {
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fn header(&self) -> &StoreHeader;
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async fn read_entry_header(&mut self) -> Result<EntryHeaderWithDataSize> {
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let number_of_columns: usize = self.header().number_of_columns;
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let mut header_bytes: Vec<u8> = vec![0; EntryHeaderWithDataSize::size(number_of_columns)];
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self.read_bytes(&mut header_bytes).await?;
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let header = EntryHeaderWithDataSize::decode(&mut header_bytes[..], number_of_columns)?;
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Ok(header)
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}
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async fn read_entry_header_at(&mut self, file_position: FilePosition) -> Result<EntryHeaderWithDataSize> {
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self.seek_to(file_position).await?;
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self.read_entry_header().await
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}
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// Returns None when file_position == eof_file_position
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async fn read_entry_at(&mut self, file_position: FilePosition) -> Result<Option<EntryDetailed<T>>>
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where T: Decode
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{
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self.seek_to(file_position).await?;
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self.next().await
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}
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// ===Iteration===
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// The following functions assume that the current file position is at a valid entry or EOF.
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// WARNING: This moves the file_position to start of the data, so you can't just call
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// next_entry_header() a bunch of times. You must move the cursor!
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async fn next_entry_header(&mut self) -> Result<Option<EntryHeaderWithDataSize>> {
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if self.is_at_eof().await? {
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return Ok(None)
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}
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let entry_header = self.read_entry_header().await?;
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Ok(Some(entry_header))
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}
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// This is meant to be used after next_entry_header() is called.
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async fn jump_from_start_of_entry_data_to_next_entry(&mut self, entry_header: &EntryHeaderWithDataSize) -> Result<FilePosition>{
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let file_position = self.seek_by(entry_header.size_of_data() as i64).await?;
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Ok(file_position)
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}
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async fn next(&mut self) -> Result<Option<EntryDetailed<T>>>
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where T: Decode
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{
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let file_position = self.current_file_position().await?;
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let Some(entry_header) = self.next_entry_header().await? else { return Ok(None) };
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let mut data_bytes: Vec<u8> = vec![0; entry_header.size_of_data()];
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self.read_bytes(&mut data_bytes).await?;
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let entry: EntryDetailed<T> =
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EntryDetailed::decode(entry_header, file_position, self.header().number_of_columns, &mut data_bytes)?;
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Ok(Some(entry))
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}
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// Like next, but only reads the column, not the whole entry.
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async fn next_at_column(&mut self, column: Column) -> Result<Option<(EntryHeaderWithDataSize, T)>>
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where T: Decode + Send
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{
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let Some(entry_header) = self.next_entry_header().await? else { return Ok(None) };
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let file_position_at_start_of_data = self.current_file_position().await?;
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// figuring out how much to decode
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let column_offset = entry_header.offset_of_column(column);
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self.seek_by(column_offset as i64).await?;
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// reading and decoding
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let mut bytes: Vec<u8> = vec![0; entry_header.data_sizes[column as usize]];
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self.read_bytes(&mut bytes).await?;
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let (value, _) =
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decode::<T>(&bytes[..])
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.map_err(|e| Error::DecodeError(DecodeErrorKind::EntryIsDeleted, e))?;
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// jumping to next entry
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self.seek_to(file_position_at_start_of_data).await?;
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self.jump_from_start_of_entry_data_to_next_entry(&entry_header).await?;
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Ok(Some((entry_header, value)))
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}
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async fn next_alive(&mut self) -> Result<Option<EntryDetailed<T>>>
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where T: Decode
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{
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while let Some(entry) = self.next().await? {
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if !entry.header.is_deleted {
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return Ok(Some(entry))
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}
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}
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Ok(None)
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}
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// ===Search===
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async fn find_first_eq_bruteforce(&mut self, column: Column, t0: &T) -> Result<Option<EntryDetailed<T>>>
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where T: Decode + PartialEq + Send + Sync
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{
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let mut file_position = self.current_file_position().await?;
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while let Some((_, t)) = self.next_at_column(column).await? {
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if &t == t0 {
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// go back and decode the whole entry
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self.seek_to(file_position).await?;
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return self.next().await
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} else {
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file_position = self.current_file_position().await?;
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}
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}
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Ok(None)
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}
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// ===Debugging===
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async fn read_entries(&mut self) -> Result<()>
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where T: Decode + std::fmt::Debug
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{
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self.seek_to_start_of_data().await?;
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while let Some(entry) = self.next().await? {
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println!("{:?}", entry);
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}
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println!("END of entries.");
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Ok(())
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}
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async fn read_all_bytes(&mut self) -> std::result::Result<Vec<u8>, std::io::Error> {
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let mut bytes: Vec<u8> = vec![];
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self.seek_to_start().await.map_err(|e| e.to_io_or_panic())?;
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self.file().read_to_end(&mut bytes).await?;
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Ok(bytes)
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}
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}
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// ===PrimitiveCursor===
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impl <T>PrimitiveCursor<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>PrimitiveCursor<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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// ===CursorWithStoreHeader===
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impl <T>CursorWithStoreHeader<T> for ReadCursor<T> {
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fn header(&self) -> &StoreHeader {
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&self.header
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}
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}
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impl <T>CursorWithStoreHeader<T> for WriteCursor<'_, T> {
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fn header(&self) -> &StoreHeader {
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&self.header
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}
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}
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impl <T> ReadCursor<T> {
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pub async fn new(store: &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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.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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data_type: store.data_type,
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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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pub async fn less_than_eq(&mut self, file_position0: FilePosition, file_position1: FilePosition) -> Result<bool> {
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todo!()
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}
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}
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impl <'cursor, T> WriteCursor<'cursor, T> {
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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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data_type: store.data_type,
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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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pub async fn connect<'header: 'cursor>(path_to_rows: &str, header: &'header mut StoreHeader) -> Result<Self>
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where T: Send
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{
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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,
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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.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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// ===Primitive Operations===
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async fn write_bytes(&mut self, bytes: &[u8]) -> Result<usize> {
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Ok(self.file.write(bytes).await?)
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}
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// ===Store Header Manipulation===
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async fn increment_total_count(&mut self) -> Result<()>
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where T: Send
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{
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self.seek_to_start().await?;
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self.seek_to(StoreHeader::TOTAL_COUNT_OFFSET as u64).await?;
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let new_count = self.header.increment_total_count();
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self.write_bytes(&encode::<usize>(&new_count)?).await?;
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Ok(())
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}
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async fn increment_deleted_count(&mut self) -> Result<()>
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where T: Send
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{
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self.seek_to_start().await?;
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self.seek_to(StoreHeader::DELETED_COUNT_OFFSET as u64).await?;
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let new_count = self.header.increment_deleted_count();
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self.write_bytes(&encode::<usize>(&new_count)?).await?;
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Ok(())
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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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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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// ===Append Entry===
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// Moves cursor to the end.
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// Returns file position to the start of the new entry.
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pub async fn append_entry(&mut self, entry: &Entry<T>) -> Result<FilePosition>
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where T: Encode + Send
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{
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self.increment_total_count().await?;
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let encoded_entry: Vec<u8> = entry.encode()?;
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let file_position = self.seek_to_end().await?;
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self.write_bytes(&encoded_entry).await?;
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let eof_file_position: FilePosition = self.current_file_position().await?;
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self.eof_file_position = eof_file_position;
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Ok(file_position)
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}
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// ===Deletion===
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pub async fn mark_deleted_at(&mut self, file_position: FilePosition) -> Result<()>
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where T: Send
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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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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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self.attempt_garbage_collection_if_necessary().await?;
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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) -> Result<Option<EntryDetailed<T>>>
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where T: Decode + PartialEq + Send + Sync
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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).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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async fn attempt_garbage_collection_if_necessary(&mut self) -> Result<()> {
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// TODO: What should be the policy? Counting size of garbage? Counting how many entries are
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// garbage?
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if self.header.deleted_count > 100 {
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todo!()
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} else {
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Ok(())
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}
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}
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async fn initiate_garbage_collection(&mut self) -> Result<usize>
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where T: Send
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{
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let table_folder = self.header.table_folder.to_string();
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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 mut 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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};
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// Creates a new cursor to the intermediate file in which we'll dump the live entries.
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// let mut cursor_to_intermediate = Self {
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// header: &mut 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 mut cursor_to_intermediate: Self = todo!();
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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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// TODO: intermediate_header does not live long enough, so after garbage collection is
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// done, we need to use it in the swap.
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cursor_to_intermediate.header = todo!();
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// In it there will be only the alive rows.
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// Afterwards we swap the files, and delete the garbage.
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todo!()
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}
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}
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