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use crate::{
heap::GHeap, nd, Arc, BTreeMap, Data, HashMap, HashSet, Mutex, PageStorage, PageStorageInfo,
RwLock, SaveOp, Storage,
};
type HX = u32; // Typical 8M cache will have 1K x 8KB pages, so 10 bits is typical, 32 should be plenty.
type Heap = GHeap<u64, u64, HX>;
/// ```Arc<Mutex<PageInfo>>```
pub type PageInfoPtr = Arc<Mutex<PageInfo>>;
/// Information for a logical page, including historic data.
pub struct PageInfo {
/// Current data for the page( None implies it is stored in underlying file ).
pub current: Option<Data>,
/// Historic data for the page. Has data for page at specified time.
/// A copy is made prior to an update, so get looks forward from access time.
pub history: BTreeMap<u64, Data>,
/// How many times has the page been used.
pub usage: u64,
/// Heap index.
pub hx: HX,
}
impl PageInfo {
fn new() -> PageInfoPtr {
Arc::new(Mutex::new(PageInfo {
current: None,
history: BTreeMap::new(),
usage: 0,
hx: HX::MAX,
}))
}
/// Increase usage.
fn inc_usage(&mut self, lpnum: u64, ah: &mut Heap) {
self.usage += 1;
if self.hx == HX::MAX {
self.hx = ah.insert(lpnum, self.usage);
} else {
ah.modify(self.hx, self.usage);
}
}
/// Get the Data for the page, checking history if not a writer.
/// Reads Data from file if necessary.
/// Result is Data and size of loaded data ( cache delta ).
fn get_data(&mut self, lpnum: u64, a: &AccessPagedData) -> (Data, usize) {
if !a.writer {
if let Some((_k, v)) = self.history.range(a.time..).next() {
return (v.clone(), 0);
}
}
if let Some(p) = &self.current {
return (p.clone(), 0);
}
// Get data from page storage.
let ps = a.spd.ps.read().unwrap();
let data = ps.get_page(lpnum);
self.current = Some(data.clone());
let len = data.len();
(data, len)
}
/// Set the page data, updating the history using the specified time and old data.
/// Result is delta of length (old size, new size)
fn set_data(&mut self, time: u64, old: Data, data: Data, do_history: bool) -> (usize, usize) {
if do_history {
self.history.insert(time, old);
}
let old = if let Some(x) = &self.current {
x.len()
} else {
0
};
let new = data.len();
self.current = if new == 0 { None } else { Some(data) };
(old, new)
}
/// Trim entry for time t that no longer need to be retained, returning whether entry was retained.
/// start is start of range for which no readers exist.
fn trim(&mut self, t: u64, start: u64) -> bool {
let first = self.history_start(t);
if first >= start {
// There is no reader that can read copy for time t, so copy can be removed.
self.history.remove(&t);
false
} else {
true
}
}
/// Returns the earliest time that would return the page for the specified time.
fn history_start(&self, t: u64) -> u64 {
if let Some((k, _)) = self.history.range(..t).next_back() {
*k + 1
} else {
0
}
}
}
/// Central store of data.
#[derive(Default)]
pub struct Stash {
/// Write time - number of writes.
pub time: u64,
/// Page number -> page info.
pub pages: HashMap<u64, PageInfoPtr>,
/// Time -> reader count. Number of readers for given time.
pub rdrs: BTreeMap<u64, usize>,
/// Time -> set of page numbers. Page copies held for given time.
pub vers: BTreeMap<u64, HashSet<u64>>,
/// Total size of current pages.
pub total: i64, // Use i64 to avoid problems with overflow.
/// trim_cache reduces total to mem_limit (or below).
pub mem_limit: usize,
/// Tracks loaded page with smallest usage.
pub min: Heap,
/// Total number of page accesses.
pub read: u64,
/// Total number of misses ( data was not already loaded ).
pub miss: u64,
}
impl Stash {
/// Set the value of the specified page for the current time.
fn set(&mut self, lpnum: u64, old: Data, data: Data) {
let time = self.time;
let u = self.vers.entry(time).or_default();
let do_history = u.insert(lpnum);
let p = self.get_pinfo(lpnum);
let diff = p.lock().unwrap().set_data(time, old, data, do_history);
self.delta(diff, false, false);
}
/// Get the PageInfoPtr for the specified page and note the page as used.
fn get_pinfo(&mut self, lpnum: u64) -> PageInfoPtr {
let p = self
.pages
.entry(lpnum)
.or_insert_with(PageInfo::new)
.clone();
p.lock().unwrap().inc_usage(lpnum, &mut self.min);
self.read += 1;
p
}
/// Register that there is a client reading the database. The result is the current time.
fn begin_read(&mut self) -> u64 {
let time = self.time;
let n = self.rdrs.entry(time).or_insert(0);
*n += 1;
time
}
/// Register that the read at the specified time has ended. Stashed pages may be freed.
fn end_read(&mut self, time: u64) {
let n = self.rdrs.get_mut(&time).unwrap();
*n -= 1;
if *n == 0 {
self.rdrs.remove(&time);
self.trim(time);
}
}
/// Register that an update operation has completed. Time is incremented.
/// Stashed pages may be freed. Returns number of pages updated.
fn end_write(&mut self) -> usize {
let result = if let Some(u) = self.vers.get(&self.time) {
u.len()
} else {
0
};
let t = self.time;
self.time = t + 1;
self.trim(t);
result
}
/// Trim historic data that is no longer required.
fn trim(&mut self, time: u64) {
let (s, r) = (self.start(time), self.retain(time));
if s != r {
let mut empty = Vec::<u64>::new();
for (t, pl) in self.vers.range_mut(s..r) {
pl.retain(|pnum| {
let p = self.pages.get(pnum).unwrap();
p.lock().unwrap().trim(*t, s)
});
if pl.is_empty() {
empty.push(*t);
}
}
for t in empty {
self.vers.remove(&t);
}
}
}
/// Calculate the start of the range of times for which there are no readers.
fn start(&self, time: u64) -> u64 {
if let Some((t, _n)) = self.rdrs.range(..time).next_back() {
1 + *t
} else {
0
}
}
/// Calculate the end of the range of times for which there are no readers.
fn retain(&self, time: u64) -> u64 {
if let Some((t, _n)) = self.rdrs.range(time..).next() {
*t
} else {
self.time
}
}
/// Adjust total.
fn delta(&mut self, d: (usize, usize), miss: bool, trim: bool) {
if miss {
self.miss += 1;
}
self.total += d.1 as i64 - d.0 as i64;
if trim {
self.trim_cache();
}
}
/// Trim cached data to configured limit.
fn trim_cache(&mut self) {
while self.total > self.mem_limit as i64 && self.min.len() > 0 {
let lpnum = self.min.pop();
let mut p = self.pages.get(&lpnum).unwrap().lock().unwrap();
p.hx = HX::MAX;
if let Some(data) = &p.current {
self.total -= data.len() as i64;
p.current = None;
}
}
}
/// Return the number of pages currently cached.
pub fn cached(&self) -> usize {
self.min.len() as usize
}
}
/// Allows logical database pages to be shared to allow concurrent readers.
pub struct SharedPagedData {
/// Permanent storage of pages.
pub ps: RwLock<Box<dyn PageStorage>>,
/// Stash of pages.
pub stash: Mutex<Stash>,
/// Info on page sizes.
pub psi: Box<dyn PageStorageInfo>,
}
impl SharedPagedData {
#[cfg(feature = "compact")]
/// Construct default SharedPageData ( default depends on compact feature ).
pub fn new(stg: Box<dyn Storage>) -> Arc<Self> {
const EP_SIZE: usize = 1024; // Size of an extension page.
const EP_MAX: usize = 16; // Maximum number of extension pages.
const SP_SIZE: usize = (EP_MAX + 1) * 8; // =136. Starter page size.
Self::new_from_ps(Box::new(crate::compact::CompactFile::new(
stg, SP_SIZE, EP_SIZE,
)))
}
#[cfg(not(feature = "compact"))]
/// Construct default SharedPageData ( default depends on compact feature ).
pub fn new(stg: Box<dyn Storage>) -> Arc<Self> {
let limits = crate::Limits::default();
Self::new_from_ps(crate::blockpagestg::BlockPageStg::new(stg, &limits))
}
/// Construct SharedPageData based on specified PageStorage ( e.g. BlockPageStg )
pub fn new_from_ps(ps: Box<dyn PageStorage>) -> Arc<Self> {
// Set a default stash memory limit of 10 MB.
let stash = Stash {
mem_limit: 10 * 1024 * 1024,
..Default::default()
};
let psi = ps.info();
Arc::new(Self {
stash: Mutex::new(stash),
ps: RwLock::new(ps),
psi,
})
}
/// Wait until current commits have been written.
pub fn wait_complete(&self) {
self.ps.read().unwrap().wait_complete();
}
}
/// Access to shared paged data.
pub struct AccessPagedData {
writer: bool,
time: u64,
/// Shared Page Data.
pub spd: Arc<SharedPagedData>,
}
impl AccessPagedData {
/// Construct access to a virtual read-only copy of the database logical pages.
pub fn new_reader(spd: Arc<SharedPagedData>) -> Self {
let time = spd.stash.lock().unwrap().begin_read();
AccessPagedData {
writer: false,
time,
spd,
}
}
/// Construct access to the database logical pages.
pub fn new_writer(spd: Arc<SharedPagedData>) -> Self {
#[cfg(feature = "log")]
{
let psi = &spd.psi;
println!(
"max page size={} half={}",
psi.max_size_page(),
psi.half_size_page()
);
}
AccessPagedData {
writer: true,
time: 0,
spd,
}
}
/// Get locked guard of stash.
pub fn stash(&self) -> std::sync::MutexGuard<'_, Stash> {
self.spd.stash.lock().unwrap()
}
/// Get the Data for the specified page.
pub fn get_data(&self, lpnum: u64) -> Data {
// Get page info.
let pinfo = self.stash().get_pinfo(lpnum);
// Read the page data.
let (data, loaded) = pinfo.lock().unwrap().get_data(lpnum, self);
if loaded > 0 {
self.stash().delta((0, loaded), true, true);
}
data
}
/// Set the data of the specified page.
pub fn set_data(&self, lpnum: u64, data: Data) {
debug_assert!(self.writer);
// Get copy of current data.
let pinfo = self.stash().get_pinfo(lpnum);
// Read the page data.
let (old, loaded) = pinfo.lock().unwrap().get_data(lpnum, self);
// Update the stash ( ensures any readers will not attempt to read the file ).
{
let s = &mut *self.stash();
if loaded > 0 {
s.delta((0, loaded), true, false);
}
s.set(lpnum, old, data.clone());
s.trim_cache();
}
// Write data to underlying file.
if data.len() > 0 {
self.spd.ps.write().unwrap().set_page(lpnum, data);
} else {
self.spd.ps.write().unwrap().drop_page(lpnum);
}
}
/// Allocate a logical page.
pub fn alloc_page(&self) -> u64 {
debug_assert!(self.writer);
self.spd.ps.write().unwrap().new_page()
}
/// Free a logical page.
pub fn free_page(&self, lpnum: u64) {
self.set_data(lpnum, nd());
}
/// Is the underlying file new (so needs to be initialised ).
pub fn is_new(&self) -> bool {
self.writer && self.spd.ps.read().unwrap().is_new()
}
/// Check whether compressing a page is worthwhile.
pub fn compress(&self, size: usize, saving: usize) -> bool {
debug_assert!(self.writer);
self.spd.psi.compress(size, saving)
}
/// Commit changes to underlying file ( or rollback logical page allocations ).
pub fn save(&self, op: SaveOp) -> usize {
debug_assert!(self.writer);
match op {
SaveOp::Save => {
self.spd.ps.write().unwrap().save();
self.stash().end_write()
}
SaveOp::RollBack => {
// Note: rollback happens before any pages are updated.
// However logical page allocations need to be rolled back.
self.spd.ps.write().unwrap().rollback();
0
}
}
}
/// Renumber a page.
#[cfg(feature = "renumber")]
pub fn renumber_page(&self, lpnum: u64) -> u64 {
assert!(self.writer);
let data = self.get_data(lpnum);
self.stash().set(lpnum, data.clone(), nd());
let lpnum2 = self.spd.ps.write().unwrap().renumber(lpnum);
debug_assert!(self
.stash()
.get_pinfo(lpnum2)
.lock()
.unwrap()
.current
.is_none());
let old2 = self.get_data(lpnum2);
self.stash().set(lpnum2, old2, data);
lpnum2
}
}
impl Drop for AccessPagedData {
fn drop(&mut self) {
if !self.writer {
self.stash().end_read(self.time);
}
}
}