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use std::collections::BinaryHeap;
#[repr(u8)]
enum WALRingType {
Null = 0x0,
Full,
First,
Middle,
Last
}
struct WALRingBlob {
crc32: u32,
rsize: u32,
rtype: WALRingType,
// payload follows
}
type WALFileId = u32;
type WALPos = u64;
#[derive(Eq, PartialEq, Copy, Clone)]
pub struct WALRingId {
start: WALPos,
end: WALPos
}
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<std::cmp::Ordering> {
Some(self.cmp(other))
}
}
pub struct WALState {
pub first_fid: u64,
pub last: WALPos,
pub block_nbit: u8,
pub file_nbit: u8,
}
pub trait WALFile {
fn allocate(&self, offset: u64, length: usize);
fn write(&self, offset: u64, data: Box<[u8]>);
fn read(&self, offset: u64, length: usize) -> Box<[u8]>;
}
pub trait WALStore {
fn open_file(&self, filename: &str, touch: bool) -> Option<Box<dyn WALFile>>;
fn remove_file(&self, filename: &str) -> bool;
fn scan_files(&self) -> Box<[&str]>;
}
struct WALFilePool<F: WALStore> {
store: F,
handles: lru::LruCache<u64, Box<dyn WALFile>>,
file_size: u64
}
impl<F: WALStore> WALFilePool<F> {
fn new(store: F, file_size: u64, cache_size: usize) -> Self {
WALFilePool {
store,
handles: lru::LruCache::new(cache_size),
file_size,
}
}
fn write(&mut self, offset: u64, data: Box<[u8]>) {
}
fn remove_file(&self, fid: u64) -> bool {
true
}
}
pub struct WALWriter<F: WALStore> {
state: WALState,
file_pool: WALFilePool<F>,
block_buffer: Box<[u8]>,
block_size: u32,
next_complete: WALPos,
io_complete: BinaryHeap<WALRingId>
}
impl<F: WALStore> WALWriter<F> {
pub fn new(state: WALState, wal_store: F, cache_size: usize) -> Self {
let mut b = Vec::new();
let block_size = 1 << (state.block_nbit as u32);
let file_size = 1 << (state.file_nbit as u64);
b.resize(block_size as usize, 0);
WALWriter{
state,
file_pool: WALFilePool::new(wal_store, file_size, cache_size),
block_buffer: b.into_boxed_slice(),
block_size,
next_complete: 0,
io_complete: BinaryHeap::new(),
}
}
/// 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(&mut self, records: &[Box<[u8]>]) -> Box<[WALRingId]> {
let mut res = Vec::new();
let mut writes = Vec::new();
let msize = std::mem::size_of::<WALRingBlob>() as u32;
// the global offest of the begining of the block
// the start of the unwritten data
let mut bbuff_start = self.state.last as u32 & (self.block_size - 1);
// the end of the unwritten data
let mut bbuff_cur = bbuff_start;
for _rec in records {
let mut rec = &_rec[..];
let mut rsize = rec.len() as u32;
let mut started = false;
while rsize > 0 {
let remain = self.block_size - bbuff_cur;
if remain > msize {
let d = remain - msize;
let blob = unsafe {std::mem::transmute::<*mut u8, &mut WALRingBlob>(
&mut self.block_buffer[bbuff_cur as usize] as *mut u8)};
let ring_start = self.state.last + (bbuff_cur - bbuff_start) as u64;
if d >= rsize {
// the remaining rec fits in the block
let payload = rec;
blob.crc32 = crc::crc32::checksum_ieee(payload);
blob.rsize = rsize;
blob.rtype = if started {WALRingType::Last} else {WALRingType::Full};
rsize = 0;
&mut self.block_buffer[bbuff_cur as usize..].copy_from_slice(payload);
bbuff_cur += rsize;
} 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 started {WALRingType::Middle} else {
started = true;
WALRingType::First
};
rsize -= d;
&mut self.block_buffer[bbuff_cur as usize..].copy_from_slice(payload);
bbuff_cur += d;
rec = &rec[d as usize..];
}
let ring_end = self.state.last + (bbuff_cur - bbuff_start) as u64;
res.push(WALRingId{start: ring_start, end: ring_end});
} 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.last,
self.block_buffer[bbuff_start as usize..]
.to_vec().into_boxed_slice()));
self.state.last += (self.block_size - bbuff_start) as u64;
bbuff_start = 0;
bbuff_cur = 0;
}
}
}
if bbuff_cur > bbuff_start {
writes.push((self.state.last,
self.block_buffer[bbuff_start as usize..bbuff_cur as usize]
.to_vec().into_boxed_slice()));
self.state.last += (bbuff_cur - bbuff_start) as u64;
}
for (off, w) in writes.into_iter() {
self.file_pool.write(off, w);
}
res.into_boxed_slice()
}
/// 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(&mut self, records: &[WALRingId]) {
for rec in records {
self.io_complete.push(*rec)
}
let orig_fid = self.state.first_fid;
while let Some(s) = self.io_complete.peek().and_then(|&e| Some(e.start)) {
if s != self.next_complete {
break
}
let m = self.io_complete.pop().unwrap();
self.next_complete = m.end
}
let next_fid = self.next_complete >> self.state.file_nbit;
for fid in orig_fid..next_fid {
self.file_pool.remove_file(fid);
}
}
}
struct WALReader {
}
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