use std::sync::{Arc, Weak}; use std::time::{Duration, Instant}; use anyhow::{anyhow, bail, Result}; use log::{debug, error, info}; use rand::prelude::*; use serde::{Deserialize, Serialize}; use tokio::sync::{watch, Notify}; use crate::cryptoblob::*; use crate::login::Credentials; use crate::timestamp::*; use crate::storage; const KEEP_STATE_EVERY: usize = 64; // Checkpointing interval constants: a checkpoint is not made earlier // than CHECKPOINT_INTERVAL time after the last one, and is not made // if there are less than CHECKPOINT_MIN_OPS new operations since last one. const CHECKPOINT_INTERVAL: Duration = Duration::from_secs(6 * 3600); const CHECKPOINT_MIN_OPS: usize = 16; // HYPOTHESIS: processes are able to communicate in a synchronous // fashion in times that are small compared to CHECKPOINT_INTERVAL. // More precisely, if a process tried to save an operation within the last // CHECKPOINT_INTERVAL, we are sure to read it from storage if it was // successfully saved (and if we don't read it, it means it has been // definitely discarded due to an error). // Keep at least two checkpoints, here three, to avoid race conditions // between processes doing .checkpoint() and those doing .sync() const CHECKPOINTS_TO_KEEP: usize = 3; const WATCH_SK: &str = "watch"; pub trait BayouState: Default + Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync + 'static { type Op: Clone + Serialize + for<'de> Deserialize<'de> + std::fmt::Debug + Send + Sync + 'static; fn apply(&self, op: &Self::Op) -> Self; } pub struct Bayou { path: String, key: Key, storage: storage::Store, checkpoint: (Timestamp, S), history: Vec<(Timestamp, S::Op, Option)>, last_sync: Option, last_try_checkpoint: Option, watch: Arc, last_sync_watch_ct: storage::RowRef, } impl Bayou { pub async fn new(creds: &Credentials, path: String) -> Result { let storage = creds.storage.build().await?; //let target = k2v_client.row(&path, WATCH_SK); let target = storage::RowRef::new(&path, WATCH_SK); let watch = K2vWatch::new(creds, target.clone()).await?; Ok(Self { path, storage, key: creds.keys.master.clone(), checkpoint: (Timestamp::zero(), S::default()), history: vec![], last_sync: None, last_try_checkpoint: None, watch, last_sync_watch_ct: target, }) } /// Re-reads the state from persistent storage backend pub async fn sync(&mut self) -> Result<()> { let new_last_sync = Some(Instant::now()); let new_last_sync_watch_ct = self.watch.rx.borrow().clone(); // 1. List checkpoints let checkpoints = self.list_checkpoints().await?; debug!("(sync) listed checkpoints: {:?}", checkpoints); // 2. Load last checkpoint if different from currently used one let checkpoint = if let Some((ts, key)) = checkpoints.last() { if *ts == self.checkpoint.0 { (*ts, None) } else { debug!("(sync) loading checkpoint: {}", key); let buf = self.storage.blob_fetch(&storage::BlobRef(key.to_string())).await?.value; debug!("(sync) checkpoint body length: {}", buf.len()); let ck = open_deserialize::(&buf, &self.key)?; (*ts, Some(ck)) } } else { (Timestamp::zero(), None) }; if self.checkpoint.0 > checkpoint.0 { bail!("Loaded checkpoint is more recent than stored one"); } if let Some(ck) = checkpoint.1 { debug!( "(sync) updating checkpoint to loaded state at {:?}", checkpoint.0 ); self.checkpoint = (checkpoint.0, ck); }; // remove from history events before checkpoint self.history = std::mem::take(&mut self.history) .into_iter() .skip_while(|(ts, _, _)| *ts < self.checkpoint.0) .collect(); // 3. List all operations starting from checkpoint let ts_ser = self.checkpoint.0.to_string(); debug!("(sync) looking up operations starting at {}", ts_ser); let ops_map = self.storage.row_fetch(&storage::Selector::Range { shard: &self.path, sort_begin: &ts_ser, sort_end: WATCH_SK }).await?; let mut ops = vec![]; for row_value in ops_map { let row = row_value.row_ref; let sort_key = row.uid.sort; let ts = sort_key.parse::().map_err(|_| anyhow!("Invalid operation timestamp: {}", sort_key))?; let val = row_value.value; if val.len() != 1 { bail!("Invalid operation, has {} values", val.len()); } match &val[0] { storage::Alternative::Value(v) => { let op = open_deserialize::(v, &self.key)?; debug!("(sync) operation {}: {:?}", sort_key, op); ops.push((ts, op)); } storage::Alternative::Tombstone => { continue; } } } ops.sort_by_key(|(ts, _)| *ts); debug!("(sync) {} operations", ops.len()); if ops.len() < self.history.len() { bail!("Some operations have disappeared from storage!"); } // 4. Check that first operation has same timestamp as checkpoint (if not zero) if self.checkpoint.0 != Timestamp::zero() && ops[0].0 != self.checkpoint.0 { bail!( "First operation in listing doesn't have timestamp that corresponds to checkpoint" ); } // 5. Apply all operations in order // Hypothesis: before the loaded checkpoint, operations haven't changed // between what's on storage and what we used to calculate the state in RAM here. let i0 = self .history .iter() .zip(ops.iter()) .take_while(|((ts1, _, _), (ts2, _))| ts1 == ts2) .count(); if ops.len() > i0 { // Remove operations from first position where histories differ self.history.truncate(i0); // Look up last calculated state which we have saved and start from there. let mut last_state = (0, &self.checkpoint.1); for (i, (_, _, state_opt)) in self.history.iter().enumerate().rev() { if let Some(state) = state_opt { last_state = (i + 1, state); break; } } // Calculate state at the end of this common part of the history let mut state = last_state.1.clone(); for (_, op, _) in self.history[last_state.0..].iter() { state = state.apply(op); } // Now, apply all operations retrieved from storage after the common part for (ts, op) in ops.drain(i0..) { state = state.apply(&op); if (self.history.len() + 1) % KEEP_STATE_EVERY == 0 { self.history.push((ts, op, Some(state.clone()))); } else { self.history.push((ts, op, None)); } } // Always save final state as result of last operation self.history.last_mut().unwrap().2 = Some(state); } // Save info that sync has been done self.last_sync = new_last_sync; self.last_sync_watch_ct = new_last_sync_watch_ct; Ok(()) } /// Does a sync() if either of the two conditions is met: /// - last sync was more than CHECKPOINT_INTERVAL/5 ago /// - a change was detected pub async fn opportunistic_sync(&mut self) -> Result<()> { let too_old = match self.last_sync { Some(t) => Instant::now() > t + (CHECKPOINT_INTERVAL / 5), _ => true, }; let changed = self.last_sync_watch_ct != *self.watch.rx.borrow(); if too_old || changed { self.sync().await?; } Ok(()) } /// Applies a new operation on the state. Once this function returns, /// the operation has been safely persisted to storage backend. /// Make sure to call `.opportunistic_sync()` before doing this, /// and even before calculating the `op` argument given here. pub async fn push(&mut self, op: S::Op) -> Result<()> { debug!("(push) add operation: {:?}", op); let ts = Timestamp::after( self.history .last() .map(|(ts, _, _)| ts) .unwrap_or(&self.checkpoint.0), ); let row_val = storage::RowVal::new( storage::RowRef::new(&self.path, &ts.to_string()), seal_serialize(&op, &self.key)?, ); self.storage.row_insert(vec![row_val]).await?; self.watch.notify.notify_one(); let new_state = self.state().apply(&op); self.history.push((ts, op, Some(new_state))); // Clear previously saved state in history if not required let hlen = self.history.len(); if hlen >= 2 && (hlen - 1) % KEEP_STATE_EVERY != 0 { self.history[hlen - 2].2 = None; } self.checkpoint().await?; Ok(()) } /// Save a new checkpoint if previous checkpoint is too old pub async fn checkpoint(&mut self) -> Result<()> { match self.last_try_checkpoint { Some(ts) if Instant::now() - ts < CHECKPOINT_INTERVAL / 5 => Ok(()), _ => { let res = self.checkpoint_internal().await; if res.is_ok() { self.last_try_checkpoint = Some(Instant::now()); } res } } } async fn checkpoint_internal(&mut self) -> Result<()> { self.sync().await?; // Check what would be the possible time for a checkpoint in the history we have let now = now_msec() as i128; let i_cp = match self .history .iter() .enumerate() .rev() .skip_while(|(_, (ts, _, _))| { (now - ts.msec as i128) < CHECKPOINT_INTERVAL.as_millis() as i128 }) .map(|(i, _)| i) .next() { Some(i) => i, None => { debug!("(cp) Oldest operation is too recent to trigger checkpoint"); return Ok(()); } }; if i_cp < CHECKPOINT_MIN_OPS { debug!("(cp) Not enough old operations to trigger checkpoint"); return Ok(()); } let ts_cp = self.history[i_cp].0; debug!( "(cp) we could checkpoint at time {} (index {} in history)", ts_cp.to_string(), i_cp ); // Check existing checkpoints: if last one is too recent, don't checkpoint again. let existing_checkpoints = self.list_checkpoints().await?; debug!("(cp) listed checkpoints: {:?}", existing_checkpoints); if let Some(last_cp) = existing_checkpoints.last() { if (ts_cp.msec as i128 - last_cp.0.msec as i128) < CHECKPOINT_INTERVAL.as_millis() as i128 { debug!( "(cp) last checkpoint is too recent: {}, not checkpointing", last_cp.0.to_string() ); return Ok(()); } } debug!("(cp) saving checkpoint at {}", ts_cp.to_string()); // Calculate state at time of checkpoint let mut last_known_state = (0, &self.checkpoint.1); for (i, (_, _, st)) in self.history[..i_cp].iter().enumerate() { if let Some(s) = st { last_known_state = (i + 1, s); } } let mut state_cp = last_known_state.1.clone(); for (_, op, _) in self.history[last_known_state.0..i_cp].iter() { state_cp = state_cp.apply(op); } // Serialize and save checkpoint let cryptoblob = seal_serialize(&state_cp, &self.key)?; debug!("(cp) checkpoint body length: {}", cryptoblob.len()); let blob_val = storage::BlobVal::new( storage::BlobRef(format!("{}/checkpoint/{}", self.path, ts_cp.to_string())), cryptoblob.into(), ); self.storage.blob_insert(blob_val).await?; // Drop old checkpoints (but keep at least CHECKPOINTS_TO_KEEP of them) let ecp_len = existing_checkpoints.len(); if ecp_len + 1 > CHECKPOINTS_TO_KEEP { let last_to_keep = ecp_len + 1 - CHECKPOINTS_TO_KEEP; // Delete blobs for (_ts, key) in existing_checkpoints[..last_to_keep].iter() { debug!("(cp) drop old checkpoint {}", key); self.storage.blob_rm(&storage::BlobRef(key.to_string())).await?; } // Delete corresponding range of operations let ts_ser = existing_checkpoints[last_to_keep].0.to_string(); self.storage.row_rm(&storage::Selector::Range { shard: &self.path, sort_begin: "", sort_end: &ts_ser }).await? } Ok(()) } pub fn state(&self) -> &S { if let Some(last) = self.history.last() { last.2.as_ref().unwrap() } else { &self.checkpoint.1 } } // ---- INTERNAL ---- async fn list_checkpoints(&self) -> Result> { let prefix = format!("{}/checkpoint/", self.path); let checkpoints_res = self.storage.blob_list(&prefix).await?; let mut checkpoints = vec![]; for object in checkpoints_res { let key = object.0; if let Some(ckid) = key.strip_prefix(&prefix) { if let Ok(ts) = ckid.parse::() { checkpoints.push((ts, key.into())); } } } checkpoints.sort_by_key(|(ts, _)| *ts); Ok(checkpoints) } } // ---- Bayou watch in K2V ---- struct K2vWatch { target: storage::RowRef, rx: watch::Receiver, notify: Notify, } impl K2vWatch { /// Creates a new watch and launches subordinate threads. /// These threads hold Weak pointers to the struct; /// they exit when the Arc is dropped. async fn new(creds: &Credentials, target: storage::RowRef) -> Result> { let storage = creds.storage.build().await?; let (tx, rx) = watch::channel::(target.clone()); let notify = Notify::new(); let watch = Arc::new(K2vWatch { target, rx, notify }); tokio::spawn(Self::background_task( Arc::downgrade(&watch), storage, tx, )); Ok(watch) } async fn background_task( self_weak: Weak, storage: storage::Store, tx: watch::Sender, ) { let mut row = match Weak::upgrade(&self_weak) { Some(this) => this.target.clone(), None => { error!("can't start loop"); return }, }; while let Some(this) = Weak::upgrade(&self_weak) { debug!( "bayou k2v watch bg loop iter ({}, {})", this.target.uid.shard, this.target.uid.sort ); tokio::select!( _ = tokio::time::sleep(Duration::from_secs(60)) => continue, update = storage.row_poll(&row) => { match update { Err(e) => { error!("Error in bayou k2v wait value changed: {}", e); tokio::time::sleep(Duration::from_secs(30)).await; } Ok(new_value) => { row = new_value.row_ref; if tx.send(row.clone()).is_err() { break; } } } } _ = this.notify.notified() => { let rand = u128::to_be_bytes(thread_rng().gen()).to_vec(); let row_val = storage::RowVal::new(row.clone(), rand); if let Err(e) = storage.row_insert(vec![row_val]).await { error!("Error in bayou k2v watch updater loop: {}", e); tokio::time::sleep(Duration::from_secs(30)).await; } } ); } info!("bayou k2v watch bg loop exiting"); } }