use std::collections::HashMap; use std::convert::TryInto; use std::sync::Arc; use std::time::Duration; use async_trait::async_trait; use serde::{Deserialize, Serialize}; use serde_bytes::ByteBuf; use futures::future::join_all; use tokio::sync::watch; use garage_db::counted_tree_hack::CountedTree; use garage_util::background::*; use garage_util::data::*; use garage_util::error::*; use garage_util::time::*; use garage_rpc::system::System; use garage_rpc::*; use crate::data::*; use crate::replication::*; use crate::schema::*; const TABLE_GC_BATCH_SIZE: usize = 1024; // GC delay for table entries: 1 day (24 hours) // (the delay before the entry is added in the GC todo list // and the moment the garbage collection actually happens) const TABLE_GC_DELAY: Duration = Duration::from_secs(24 * 3600); pub(crate) struct TableGc { system: Arc, data: Arc>, endpoint: Arc>, } #[derive(Serialize, Deserialize)] enum GcRpc { Update(Vec), DeleteIfEqualHash(Vec<(ByteBuf, Hash)>), Ok, } impl Rpc for GcRpc { type Response = Result; } impl TableGc { pub(crate) fn new(system: Arc, data: Arc>) -> Arc { let endpoint = system .netapp .endpoint(format!("garage_table/gc.rs/Rpc:{}", F::TABLE_NAME)); let gc = Arc::new(Self { system, data, endpoint, }); gc.endpoint.set_handler(gc.clone()); gc } pub(crate) fn spawn_workers(self: &Arc, bg: &BackgroundRunner) { bg.spawn_worker(GcWorker::new(self.clone())); } async fn gc_loop_iter(&self) -> Result, Error> { let now = now_msec(); // List entries in the GC todo list // These entries are put there when a tombstone is inserted in the table // (see update_entry in data.rs) let mut candidates = vec![]; for entry_kv in self.data.gc_todo.iter()? { let (k, vhash) = entry_kv?; let todo_entry = GcTodoEntry::parse(&k, &vhash); if todo_entry.deletion_time() > now { if candidates.is_empty() { // If the earliest entry in the todo list shouldn't yet be processed, // return a duration to wait in the loop return Ok(Some(Duration::from_millis( todo_entry.deletion_time() - now, ))); } else { // Otherwise we have some entries to process, do a normal iteration. break; } } candidates.push(todo_entry); if candidates.len() >= 2 * TABLE_GC_BATCH_SIZE { break; } } let mut entries = vec![]; let mut excluded = vec![]; for mut todo_entry in candidates { // Check if the tombstone is still the current value of the entry. // If not, we don't actually want to GC it, and we will remove it // from the gc_todo table later (below). let vhash = todo_entry.value_hash; todo_entry.value = self .data .store .get(&todo_entry.key[..])? .filter(|v| blake2sum(&v[..]) == vhash) .map(|v| v.to_vec()); if todo_entry.value.is_some() { entries.push(todo_entry); if entries.len() >= TABLE_GC_BATCH_SIZE { break; } } else { excluded.push(todo_entry); } } // Remove from gc_todo entries for tombstones where we have // detected that the current value has changed and // is no longer a tombstone. for entry in excluded { entry.remove_if_equal(&self.data.gc_todo)?; } // Remaining in `entries` is the list of entries we want to GC, // and for which they are still currently tombstones in the table. if entries.is_empty() { // Nothing to do in this iteration (no entries present) // Wait for a default delay of 60 seconds return Ok(Some(Duration::from_secs(60))); } debug!("({}) GC: doing {} items", F::TABLE_NAME, entries.len()); // Split entries to GC by the set of nodes on which they are stored. // Here we call them partitions but they are not exactly // the same as partitions as defined in the ring: those partitions // are defined by the first 8 bits of the hash, but two of these // partitions can be stored on the same set of nodes. // Here we detect when entries are stored on the same set of nodes: // even if they are not in the same 8-bit partition, we can still // handle them together. let mut partitions = HashMap::new(); for entry in entries { let pkh = Hash::try_from(&entry.key[..32]).unwrap(); let mut nodes = self.data.replication.storage_nodes(&pkh); nodes.retain(|x| *x != self.system.id); nodes.sort(); if !partitions.contains_key(&nodes) { partitions.insert(nodes.clone(), vec![]); } partitions.get_mut(&nodes).unwrap().push(entry); } // For each set of nodes that contains some items, // ensure they are aware of the tombstone status, and once they // are, instruct them to delete the entries. let resps = join_all( partitions .into_iter() .map(|(nodes, items)| self.try_send_and_delete(nodes, items)), ) .await; // Collect errors and return a single error value even if several // errors occurred. let mut errs = vec![]; for resp in resps { if let Err(e) = resp { errs.push(e); } } if errs.is_empty() { Ok(None) } else { Err(Error::Message( errs.into_iter() .map(|x| format!("{}", x)) .collect::>() .join(", "), )) .err_context("in try_send_and_delete in table GC:") } } async fn try_send_and_delete( &self, nodes: Vec, mut items: Vec, ) -> Result<(), Error> { let n_items = items.len(); // Strategy: we first send all of the values to the remote nodes, // to ensure that they are aware of the tombstone state, // and that the previous state was correctly overwritten // (if they have a newer state that overrides the tombstone, that's fine). // Second, once everyone is at least at the tombstone state, // we instruct everyone to delete the tombstone IF that is still their current state. // If they are now at a different state, it means that that state overrides the // tombstone in the CRDT lattice, and it will be propagated back to us at some point // (either just a regular update that hasn't reached us yet, or later when the // table is synced). // Here, we store in updates all of the tombstones to send for step 1, // and in deletes the list of keys and hashes of value for step 2. let mut updates = vec![]; let mut deletes = vec![]; for item in items.iter_mut() { updates.push(ByteBuf::from(item.value.take().unwrap())); deletes.push((ByteBuf::from(item.key.clone()), item.value_hash)); } // Step 1: ensure everyone is at least at tombstone in CRDT lattice // Here the quorum is nodes.len(): we cannot tolerate even a single failure, // otherwise old values before the tombstone might come back in the data. // GC'ing is not a critical function of the system, so it's not a big // deal if we can't do it right now. self.system .rpc_helper() .try_call_many( &self.endpoint, &nodes, GcRpc::Update(updates), RequestStrategy::with_priority(PRIO_BACKGROUND).with_quorum(nodes.len()), ) .await .err_context("GC: send tombstones")?; info!( "({}) GC: {} items successfully pushed, will try to delete.", F::TABLE_NAME, n_items ); // Step 2: delete tombstones everywhere. // Here we also fail if even a single node returns a failure: // it means that the garbage collection wasn't completed and has // to be retried later. self.system .rpc_helper() .try_call_many( &self.endpoint, &nodes, GcRpc::DeleteIfEqualHash(deletes), RequestStrategy::with_priority(PRIO_BACKGROUND).with_quorum(nodes.len()), ) .await .err_context("GC: remote delete tombstones")?; // GC has been successfull for all of these entries. // We now remove them all from our local table and from the GC todo list. for item in items { self.data .delete_if_equal_hash(&item.key[..], item.value_hash) .err_context("GC: local delete tombstones")?; item.remove_if_equal(&self.data.gc_todo) .err_context("GC: remove from todo list after successfull GC")?; } Ok(()) } } #[async_trait] impl EndpointHandler for TableGc { async fn handle(self: &Arc, message: &GcRpc, _from: NodeID) -> Result { match message { GcRpc::Update(items) => { self.data.update_many(items)?; Ok(GcRpc::Ok) } GcRpc::DeleteIfEqualHash(items) => { for (key, vhash) in items.iter() { self.data.delete_if_equal_hash(&key[..], *vhash)?; } Ok(GcRpc::Ok) } m => Err(Error::unexpected_rpc_message(m)), } } } struct GcWorker { gc: Arc>, wait_delay: Duration, } impl GcWorker { fn new(gc: Arc>) -> Self { Self { gc, wait_delay: Duration::from_secs(0), } } } #[async_trait] impl Worker for GcWorker { fn name(&self) -> String { format!("{} GC", F::TABLE_NAME) } fn status(&self) -> WorkerStatus { WorkerStatus { queue_length: Some(self.gc.data.gc_todo_len().unwrap_or(0) as u64), ..Default::default() } } async fn work(&mut self, _must_exit: &mut watch::Receiver) -> Result { match self.gc.gc_loop_iter().await? { None => Ok(WorkerState::Busy), Some(delay) => { self.wait_delay = delay; Ok(WorkerState::Idle) } } } async fn wait_for_work(&mut self) -> WorkerState { tokio::time::sleep(self.wait_delay).await; WorkerState::Busy } } /// An entry stored in the gc_todo db tree associated with the table /// Contains helper function for parsing, saving, and removing /// such entry in the db /// /// Format of an entry: /// - key = 8 bytes: timestamp of tombstone /// (used to implement GC delay) /// n bytes: key in the main data table /// - value = hash of the table entry to delete (the tombstone) /// for verification purpose, because we don't want to delete /// things that aren't tombstones pub(crate) struct GcTodoEntry { tombstone_timestamp: u64, key: Vec, value_hash: Hash, value: Option>, } impl GcTodoEntry { /// Creates a new GcTodoEntry (not saved in the db) from its components: /// the key of an entry in the table, and the hash of the associated /// serialized value pub(crate) fn new(key: Vec, value_hash: Hash) -> Self { Self { tombstone_timestamp: now_msec(), key, value_hash, value: None, } } /// Parses a GcTodoEntry from a (k, v) pair stored in the gc_todo tree pub(crate) fn parse(db_k: &[u8], db_v: &[u8]) -> Self { Self { tombstone_timestamp: u64::from_be_bytes(db_k[0..8].try_into().unwrap()), key: db_k[8..].to_vec(), value_hash: Hash::try_from(db_v).unwrap(), value: None, } } /// Saves the GcTodoEntry in the gc_todo tree pub(crate) fn save(&self, gc_todo_tree: &CountedTree) -> Result<(), Error> { gc_todo_tree.insert(self.todo_table_key(), self.value_hash.as_slice())?; Ok(()) } /// Removes the GcTodoEntry from the gc_todo tree if the /// hash of the serialized value is the same here as in the tree. /// This is usefull to remove a todo entry only under the condition /// that it has not changed since the time it was read, i.e. /// what we have to do is still the same pub(crate) fn remove_if_equal(&self, gc_todo_tree: &CountedTree) -> Result<(), Error> { gc_todo_tree.compare_and_swap::<_, _, &[u8]>( &self.todo_table_key(), Some(self.value_hash), None, )?; Ok(()) } fn todo_table_key(&self) -> Vec { [ &u64::to_be_bytes(self.tombstone_timestamp)[..], &self.key[..], ] .concat() } fn deletion_time(&self) -> u64 { self.tombstone_timestamp + TABLE_GC_DELAY.as_millis() as u64 } }