Move block RC code to separate `rc.rs`

1 files changed, 15 insertions, 136 deletions

diff --git a/src/block/manager.rs b/src/block/manager.rs
index 9665a306..feb6fb9d 100644
--- a/src/block/manager.rs
+++ b/src/block/manager.rs
@@ -31,6 +31,7 @@ use garage_table::replication::{TableReplication, TableShardedReplication};
 
 use crate::metrics::*;
 use crate::block::*;
+use crate::rc::*;
 
 /// Size under which data will be stored inlined in database instead of as files
 pub const INLINE_THRESHOLD: usize = 3072;
@@ -51,7 +52,7 @@ const RESYNC_RETRY_DELAY: Duration = Duration::from_secs(60);
 // The delay between the moment when the reference counter
 // drops to zero, and the moment where we allow ourselves
 // to delete the block locally.
-const BLOCK_GC_DELAY: Duration = Duration::from_secs(600);
+pub(crate) const BLOCK_GC_DELAY: Duration = Duration::from_secs(600);
 
 /// RPC messages used to share blocks of data between nodes
 #[derive(Debug, Serialize, Deserialize)]
@@ -86,7 +87,7 @@ pub struct BlockManager {
 
 	mutation_lock: Mutex<BlockManagerLocked>,
 
-	rc: sled::Tree,
+	pub rc: BlockRc,
 
 	resync_queue: SledCountedTree,
 	resync_notify: Notify,
@@ -114,6 +115,7 @@ impl BlockManager {
 		let rc = db
 			.open_tree("block_local_rc")
 			.expect("Unable to open block_local_rc tree");
+		let rc = BlockRc::new(rc);
 
 		let resync_queue = db
 			.open_tree("block_local_resync_queue")
@@ -213,7 +215,7 @@ impl BlockManager {
 	/// to fix any mismatch between the two.
 	pub async fn repair_data_store(&self, must_exit: &watch::Receiver<bool>) -> Result<(), Error> {
 		// 1. Repair blocks from RC table.
-		for (i, entry) in self.rc.iter().enumerate() {
+		for (i, entry) in self.rc.rc.iter().enumerate() {
 			let (hash, _) = entry?;
 			let hash = Hash::try_from(&hash[..]).unwrap();
 			self.put_to_resync(&hash, Duration::from_secs(0))?;
@@ -261,7 +263,7 @@ impl BlockManager {
 
 	/// Get number of items in the refcount table
 	pub fn rc_len(&self) -> usize {
-		self.rc.len()
+		self.rc.rc.len()
 	}
 
 	//// ----- Managing the reference counter ----
@@ -269,11 +271,7 @@ impl BlockManager {
 	/// Increment the number of time a block is used, putting it to resynchronization if it is
 	/// required, but not known
 	pub fn block_incref(&self, hash: &Hash) -> Result<(), Error> {
-		let old_rc = self
-			.rc
-			.fetch_and_update(&hash, |old| RcEntry::parse_opt(old).increment().serialize())?;
-		let old_rc = RcEntry::parse_opt(old_rc);
-		if old_rc.is_zero() {
+		if self.rc.block_incref(hash)? {
 			// When the reference counter is incremented, there is
 			// normally a node that is responsible for sending us the
 			// data of the block. However that operation may fail,
@@ -287,35 +285,17 @@ impl BlockManager {
 
 	/// Decrement the number of time a block is used
 	pub fn block_decref(&self, hash: &Hash) -> Result<(), Error> {
-		let new_rc = self
-			.rc
-			.update_and_fetch(&hash, |old| RcEntry::parse_opt(old).decrement().serialize())?;
-		let new_rc = RcEntry::parse_opt(new_rc);
-		if let RcEntry::Deletable { .. } = new_rc {
+		if self.rc.block_decref(hash)? {
+			// When the RC is decremented, it might drop to zero,
+			// indicating that we don't need the block.
+			// There is a delay before we garbage collect it;
+			// make sure that it is handled in the resync loop
+			// after that delay has passed.
 			self.put_to_resync(hash, BLOCK_GC_DELAY + Duration::from_secs(10))?;
 		}
 		Ok(())
 	}
 
-	/// Read a block's reference count
-	fn get_block_rc(&self, hash: &Hash) -> Result<RcEntry, Error> {
-		Ok(RcEntry::parse_opt(self.rc.get(hash.as_ref())?))
-	}
-
-	/// Delete an entry in the RC table if it is deletable and the
-	/// deletion time has passed
-	fn clear_deleted_block_rc(&self, hash: &Hash) -> Result<(), Error> {
-		let now = now_msec();
-		self.rc.update_and_fetch(&hash, |rcval| {
-			let updated = match RcEntry::parse_opt(rcval) {
-				RcEntry::Deletable { at_time } if now > at_time => RcEntry::Absent,
-				v => v,
-			};
-			updated.serialize()
-		})?;
-		Ok(())
-	}
-
 	// ---- Reading and writing blocks locally ----
 
 	/// Write a block to disk
@@ -659,7 +639,7 @@ impl BlockManager {
 				.delete_if_unneeded(hash, self)
 				.await?;
 
-			self.clear_deleted_block_rc(hash)?;
+			self.rc.clear_deleted_block_rc(hash)?;
 		}
 
 		if needed.is_nonzero() && !exists {
@@ -773,7 +753,7 @@ impl BlockManagerLocked {
 		mgr: &BlockManager,
 	) -> Result<BlockStatus, Error> {
 		let exists = mgr.is_block_compressed(hash).await.is_ok();
-		let needed = mgr.get_block_rc(hash)?;
+		let needed = mgr.rc.get_block_rc(hash)?;
 
 		Ok(BlockStatus { exists, needed })
 	}
@@ -869,107 +849,6 @@ impl BlockManagerLocked {
 	}
 }
 
-/// Describes the state of the reference counter for a block
-#[derive(Clone, Copy, Debug)]
-enum RcEntry {
-	/// Present: the block has `count` references, with `count` > 0.
-	///
-	/// This is stored as u64::to_be_bytes(count)
-	Present { count: u64 },
-
-	/// Deletable: the block has zero references, and can be deleted
-	/// once time (returned by now_msec) is larger than at_time
-	/// (in millis since Unix epoch)
-	///
-	/// This is stored as [0u8; 8] followed by u64::to_be_bytes(at_time),
-	/// (this allows for the data format to be backwards compatible with
-	/// previous Garage versions that didn't have this intermediate state)
-	Deletable { at_time: u64 },
-
-	/// Absent: the block has zero references, and can be deleted
-	/// immediately
-	Absent,
-}
-
-impl RcEntry {
-	fn parse(bytes: &[u8]) -> Self {
-		if bytes.len() == 8 {
-			RcEntry::Present {
-				count: u64::from_be_bytes(bytes.try_into().unwrap()),
-			}
-		} else if bytes.len() == 16 {
-			RcEntry::Deletable {
-				at_time: u64::from_be_bytes(bytes[8..16].try_into().unwrap()),
-			}
-		} else {
-			panic!("Invalid RC entry: {:?}, database is corrupted. This is an error Garage is currently unable to recover from. Sorry, and also please report a bug.",
-				bytes
-			)
-		}
-	}
-
-	fn parse_opt<V: AsRef<[u8]>>(bytes: Option<V>) -> Self {
-		bytes
-			.map(|b| Self::parse(b.as_ref()))
-			.unwrap_or(Self::Absent)
-	}
-
-	fn serialize(self) -> Option<Vec<u8>> {
-		match self {
-			RcEntry::Present { count } => Some(u64::to_be_bytes(count).to_vec()),
-			RcEntry::Deletable { at_time } => {
-				Some([u64::to_be_bytes(0), u64::to_be_bytes(at_time)].concat())
-			}
-			RcEntry::Absent => None,
-		}
-	}
-
-	fn increment(self) -> Self {
-		let old_count = match self {
-			RcEntry::Present { count } => count,
-			_ => 0,
-		};
-		RcEntry::Present {
-			count: old_count + 1,
-		}
-	}
-
-	fn decrement(self) -> Self {
-		match self {
-			RcEntry::Present { count } => {
-				if count > 1 {
-					RcEntry::Present { count: count - 1 }
-				} else {
-					RcEntry::Deletable {
-						at_time: now_msec() + BLOCK_GC_DELAY.as_millis() as u64,
-					}
-				}
-			}
-			del => del,
-		}
-	}
-
-	fn is_zero(&self) -> bool {
-		matches!(self, RcEntry::Deletable { .. } | RcEntry::Absent)
-	}
-
-	fn is_nonzero(&self) -> bool {
-		!self.is_zero()
-	}
-
-	fn is_deletable(&self) -> bool {
-		match self {
-			RcEntry::Present { .. } => false,
-			RcEntry::Deletable { at_time } => now_msec() > *at_time,
-			RcEntry::Absent => true,
-		}
-	}
-
-	fn is_needed(&self) -> bool {
-		!self.is_deletable()
-	}
-}
-
 /// Counts the number of errors when resyncing a block,
 /// and the time of the last try.
 /// Used to implement exponential backoff.