use async_trait::async_trait; use futures::future::{self, FutureExt, TryFutureExt}; use std::cell::{RefCell, UnsafeCell}; use std::collections::BinaryHeap; use std::future::Future; use std::mem::MaybeUninit; use std::pin::Pin; #[repr(u8)] enum WALRingType { #[allow(dead_code)] Null = 0x0, Full, First, Middle, Last, } #[repr(packed)] struct WALRingBlob { crc32: u32, rsize: u32, rtype: WALRingType, // payload follows } pub type WALBytes = Box<[u8]>; pub type WALFileId = u64; pub type WALPos = u64; #[derive(Eq, PartialEq, Copy, Clone, Debug, Hash)] pub struct WALRingId { start: WALPos, end: WALPos, } impl WALRingId { pub fn empty_id() -> Self { WALRingId { start: 0, end: 0 } } pub fn get_start(&self) -> WALPos { self.start } pub fn get_end(&self) -> WALPos { self.end } } impl Ord for WALRingId { fn cmp(&self, other: &WALRingId) -> std::cmp::Ordering { other .start .cmp(&self.start) .then_with(|| other.end.cmp(&self.end)) } } impl PartialOrd for WALRingId { fn partial_cmp(&self, other: &WALRingId) -> Option { Some(self.cmp(other)) } } /// the state for a WAL writer struct WALState { /// the first file id of WAL first_fid: WALFileId, /// the next position for a record, addressed in the entire WAL space next: WALPos, /// number of bits for a file file_nbit: u64, next_complete: WALPos, io_complete: BinaryHeap, } #[async_trait(?Send)] pub trait WALFile { /// Initialize the file space in [offset, offset + length) to zero. async fn allocate(&self, offset: WALPos, length: usize) -> Result<(), ()>; /// Write data with offset. We assume all previous `allocate/truncate` invocations are visible /// if ordered earlier (should be guaranteed by most OS). Additionally, the final write caused /// by each invocation of this function should be _atomic_ (the entire single write should be /// all or nothing). async fn write(&self, offset: WALPos, data: WALBytes) -> Result<(), ()>; /// Read data with offset. Return Ok(None) when it reaches EOF. fn read( &self, offset: WALPos, length: usize, ) -> Result, ()>; /// Truncate a file to a specified length. fn truncate(&self, length: usize) -> Result<(), ()>; } #[async_trait(?Send)] pub trait WALStore { type FileNameIter: Iterator; /// Open a file given the filename, create the file if not exists when `touch` is `true`. async fn open_file( &self, filename: &str, touch: bool, ) -> Result, ()>; /// Unlink a file given the filename. async fn remove_file(&self, filename: String) -> Result<(), ()>; /// Enumerate all WAL filenames. It should include all WAL files that are previously opened /// (created) but not removed. The list could be unordered. fn enumerate_files(&self) -> Result; /// Apply the payload during recovery. An invocation of the callback waits the application for /// redoing the given operation to ensure its state is consistent. We assume the necessary /// changes by the payload has already been persistent when the callback returns. fn apply_payload( &self, payload: WALBytes, ringid: WALRingId, ) -> Result<(), ()>; } /// The middle layer that manages WAL file handles and invokes public trait functions to actually /// manipulate files and their contents. struct WALFilePool { store: F, handles: RefCell>>, last_write: UnsafeCell>>>>>, last_peel: UnsafeCell>>>>>, file_nbit: u64, file_size: u64, block_nbit: u64, } impl WALFilePool { fn new(store: F, file_nbit: u8, block_nbit: u8, cache_size: usize) -> Self { let file_nbit = file_nbit as u64; let block_nbit = block_nbit as u64; WALFilePool { store, handles: RefCell::new(lru::LruCache::new(cache_size)), last_write: UnsafeCell::new(MaybeUninit::new(Box::pin( future::ready(Ok(())), ))), last_peel: UnsafeCell::new(MaybeUninit::new(Box::pin( future::ready(Ok(())), ))), file_nbit, file_size: 1 << (file_nbit as u64), block_nbit, } } fn get_fname(fid: WALFileId) -> String { format!("{:08x}.log", fid) } fn get_file( &self, fid: u64, touch: bool, ) -> impl Future> { async move { if let Some(h) = self.handles.borrow_mut().get(&fid) { return Ok(unsafe { &*(&**h as *const dyn WALFile) }); } let h = { let mut handles = self.handles.borrow_mut(); handles.put( fid, self.store.open_file(&Self::get_fname(fid), touch).await?, ); &**handles.get(&fid).unwrap() as *const dyn WALFile }; Ok(unsafe { &*(h) }) } } fn get_fid(&mut self, fname: &str) -> WALFileId { scan_fmt!(fname, "{x}.log", [hex WALFileId]).unwrap() } fn write<'a>( &'a mut self, writes: Vec<(WALPos, WALBytes)>, ) -> Vec> + 'a>>> { let file_size = self.file_size; let file_nbit = self.file_nbit; let meta: Vec<(u64, u64)> = writes .iter() .map(|(off, w)| ((*off) >> file_nbit, w.len() as u64)) .collect(); let mut files: Vec + 'a>>> = Vec::new(); for &(fid, _) in meta.iter() { files.push(Box::pin(self.get_file(fid, true)) as Pin + 'a>>) } let mut fid = writes[0].0 >> file_nbit; let mut alloc_start = writes[0].0 & (self.file_size - 1); let mut alloc_end = alloc_start + writes[0].1.len() as u64; let last_write = unsafe { std::mem::replace( &mut *self.last_write.get(), std::mem::MaybeUninit::uninit(), ) .assume_init() }; // pre-allocate the file space let alloc = async move { last_write.await?; let mut last_h: Option< Pin> + 'a>>, > = None; for ((next_fid, wl), h) in meta.into_iter().zip(files.into_iter()) { if let Some(lh) = last_h.take() { if next_fid != fid { lh.await? .allocate( alloc_start, (alloc_end - alloc_start) as usize, ) .await?; last_h = Some(h); alloc_start = 0; alloc_end = alloc_start + wl; fid = next_fid; } else { last_h = Some(lh); alloc_end += wl; } } else { last_h = Some(h); } } if let Some(lh) = last_h { lh.await? .allocate(alloc_start, (alloc_end - alloc_start) as usize) .await? } Ok(()) }; let mut res = Vec::new(); let mut prev = Box::pin(alloc) as Pin + 'a>>; for (off, w) in writes.into_iter() { let f = self.get_file(off >> file_nbit, true); let w = (async move { prev.await?; f.await?.write(off & (file_size - 1), w).await }) .shared(); prev = Box::pin(w.clone()); res.push(Box::pin(w) as Pin + 'a>>) } unsafe { (*self.last_write.get()) = MaybeUninit::new(std::mem::transmute::< Pin + 'a>>, Pin + 'static>>, >(prev)) } res } fn remove_files<'a>(&'a mut self, fid_s: u64, fid_e: u64) -> impl Future> + 'a { let last_peel = unsafe { std::mem::replace( &mut *self.last_peel.get(), std::mem::MaybeUninit::uninit(), ) .assume_init() }; let mut removes = Vec::new(); for fid in fid_s..fid_e { removes.push(self.store.remove_file(Self::get_fname(fid)) as Pin + 'a>>) } let p = async move { last_peel.await?; for r in removes.into_iter() { r.await? } Ok(()) }.shared(); unsafe { (*self.last_peel.get()) = MaybeUninit::new( std::mem::transmute( Box::pin(p.clone()) as Pin + 'a>>)) } p } fn reset(&mut self) { self.handles.borrow_mut().clear() } } pub struct WALWriter { state: WALState, file_pool: WALFilePool, block_buffer: WALBytes, block_size: u32, msize: usize, } impl WALWriter { fn new(state: WALState, file_pool: WALFilePool) -> Self { let mut b = Vec::new(); let block_size = 1 << file_pool.block_nbit as u32; let msize = std::mem::size_of::(); b.resize(block_size as usize, 0); WALWriter { state, file_pool, block_buffer: b.into_boxed_slice(), block_size, msize, } } /// Submit a sequence of records to WAL; WALStore/WALFile callbacks are invoked before the /// function returns. The caller then has the knowledge of WAL writes so it should defer /// actual data writes after WAL writes. pub fn grow<'a, T: AsRef<[WALBytes]>>( &'a mut self, records: T, ) -> Vec> + 'a> { let mut res = Vec::new(); let mut writes = Vec::new(); let msize = self.msize as u32; // the global offest of the begining of the block // the start of the unwritten data let mut bbuff_start = self.state.next as u32 & (self.block_size - 1); // the end of the unwritten data let mut bbuff_cur = bbuff_start; for _rec in records.as_ref() { let mut rec = &_rec[..]; let mut rsize = rec.len() as u32; let mut ring_start = None; while rsize > 0 { let remain = self.block_size - bbuff_cur; if remain > msize { let d = remain - msize; let rs0 = self.state.next + (bbuff_cur - bbuff_start) as u64; let blob = unsafe { std::mem::transmute::<*mut u8, &mut WALRingBlob>( (&mut self.block_buffer[bbuff_cur as usize..]) .as_mut_ptr(), ) }; bbuff_cur += msize; if d >= rsize { // the remaining rec fits in the block let payload = rec; blob.crc32 = crc::crc32::checksum_ieee(payload); blob.rsize = rsize; let (rs, rt) = if let Some(rs) = ring_start.take() { (rs, WALRingType::Last) } else { (rs0, WALRingType::Full) }; blob.rtype = rt; &mut self.block_buffer[bbuff_cur as usize.. bbuff_cur as usize + payload.len()] .copy_from_slice(payload); bbuff_cur += rsize; rsize = 0; let end = self.state.next + (bbuff_cur - bbuff_start) as u64; res.push((WALRingId { start: rs, end }, Vec::new())); } else { // the remaining block can only accommodate partial rec let payload = &rec[..d as usize]; blob.crc32 = crc::crc32::checksum_ieee(payload); blob.rsize = d; blob.rtype = if ring_start.is_some() { WALRingType::Middle } else { ring_start = Some(rs0); WALRingType::First }; &mut self.block_buffer[bbuff_cur as usize.. bbuff_cur as usize + payload.len()] .copy_from_slice(payload); bbuff_cur += d; rsize -= d; rec = &rec[d as usize..]; } } else { // add padding space by moving the point to the end of the block bbuff_cur = self.block_size; } if bbuff_cur == self.block_size { writes.push(( self.state.next, self.block_buffer[bbuff_start as usize..] .to_vec() .into_boxed_slice(), )); self.state.next += (self.block_size - bbuff_start) as u64; bbuff_start = 0; bbuff_cur = 0; } } } if bbuff_cur > bbuff_start { writes.push(( self.state.next, self.block_buffer[bbuff_start as usize..bbuff_cur as usize] .to_vec() .into_boxed_slice(), )); self.state.next += (bbuff_cur - bbuff_start) as u64; } // mark the block info for each record let mut i = 0; 'outer: for (j, (off, w)) in writes.iter().enumerate() { let blk_s = *off; let blk_e = blk_s + w.len() as u64; while res[i].0.end <= blk_s { i += 1; if i >= res.len() { break 'outer; } } while res[i].0.start < blk_e { res[i].1.push(j); if res[i].0.end >= blk_e { break; } i += 1; if i >= res.len() { break 'outer; } } } let writes: Vec> = self .file_pool .write(writes) .into_iter() .map(move |f| async move { f.await }.shared()) .collect(); let res = res .into_iter() .map(|(ringid, blks)| { future::try_join_all( blks.into_iter().map(|idx| writes[idx].clone()), ) .or_else(|_| future::ready(Err(()))) .and_then(move |_| future::ready(Ok(ringid))) }) .collect(); res } /// Inform the WALWriter that data writes (specified by a slice of (offset, length) tuples) are /// complete so that it could automatically remove obsolete WAL files. pub fn peel<'a, T: AsRef<[WALRingId]>>( &'a mut self, records: T, ) -> impl Future> + 'a { let msize = self.msize as u64; let block_size = self.block_size as u64; let state = &mut self.state; for rec in records.as_ref() { state.io_complete.push(*rec); } let orig_fid = state.first_fid; while let Some(s) = state.io_complete.peek().and_then(|&e| Some(e.start)) { if s != state.next_complete { break; } let mut m = state.io_complete.pop().unwrap(); let block_remain = block_size - (m.end & (block_size - 1)); if block_remain <= msize as u64 { m.end += block_remain } state.next_complete = m.end } let next_fid = state.next_complete >> state.file_nbit; state.first_fid = next_fid; self.file_pool.remove_files(orig_fid, next_fid) } } pub struct WALLoader { file_nbit: u8, block_nbit: u8, cache_size: usize, msize: usize, filename_fmt: regex::Regex, } impl WALLoader { pub fn new(file_nbit: u8, block_nbit: u8, cache_size: usize) -> Self { let msize = std::mem::size_of::(); assert!(file_nbit > block_nbit); assert!(msize < 1 << block_nbit); let filename_fmt = regex::Regex::new(r"[0-9a-f]+\.log").unwrap(); WALLoader { file_nbit, block_nbit, cache_size, msize, filename_fmt, } } /// Recover by reading the WAL log files. pub fn recover(self, store: F) -> Result, ()> { let mut file_pool = WALFilePool::new( store, self.file_nbit, self.block_nbit, self.cache_size, ); let block_size = 1 << file_pool.block_nbit; let msize = self.msize as u32; let mut logfiles: Vec = file_pool .store .enumerate_files()? .filter(|f| self.filename_fmt.is_match(f)) .collect(); // TODO: check for missing logfiles logfiles.sort(); let mut chunks = None; for fname in logfiles.into_iter() { let fid = file_pool.get_fid(&fname); let f = futures::executor::block_on(file_pool.get_file(fid, false))?; let mut off = 0; while let Some(header_raw) = f.read(off, msize as usize)? { let ringid_start = (fid << file_pool.file_nbit) + off; off += msize as u64; let header = unsafe { std::mem::transmute::<*const u8, &WALRingBlob>( header_raw.as_ptr(), ) }; let rsize = header.rsize; match header.rtype { WALRingType::Full => { assert!(chunks.is_none()); let payload = f.read(off, rsize as usize)?.ok_or(())?; off += rsize as u64; file_pool.store.apply_payload( payload, WALRingId { start: ringid_start, end: (fid << file_pool.file_nbit) + off, }, )?; } WALRingType::First => { assert!(chunks.is_none()); chunks = Some(( vec![f.read(off, rsize as usize)?.ok_or(())?], ringid_start, )); off += rsize as u64; } WALRingType::Middle => { if let Some((chunks, _)) = &mut chunks { chunks .push(f.read(off, rsize as usize)?.ok_or(())?); } // otherwise ignore the leftover off += rsize as u64; } WALRingType::Last => { if let Some((mut chunks, ringid_start)) = chunks.take() { chunks .push(f.read(off, rsize as usize)?.ok_or(())?); off += rsize as u64; let mut payload = Vec::new(); payload.resize( chunks.iter().fold(0, |acc, v| acc + v.len()), 0, ); let mut ps = &mut payload[..]; for c in chunks { ps[..c.len()].copy_from_slice(&*c); ps = &mut ps[c.len()..]; } file_pool.store.apply_payload( payload.into_boxed_slice(), WALRingId { start: ringid_start, end: (fid << file_pool.file_nbit) + off, }, )?; } // otherwise ignore the leftover else { off += rsize as u64; } } WALRingType::Null => break, } let block_remain = block_size - (off & (block_size - 1)); if block_remain <= msize as u64 { off += block_remain; } } f.truncate(0)?; futures::executor::block_on(file_pool.store.remove_file(fname))?; } file_pool.reset(); Ok(WALWriter::new( WALState { first_fid: 0, next: 0, file_nbit: file_pool.file_nbit, next_complete: 0, io_complete: BinaryHeap::new(), }, file_pool, )) } }