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Safety: never voluntarily delete block in 10min interval after RC reaches zero

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This commit is contained in:
Alex Auvolat 2021-10-28 14:32:55 +02:00
parent cc255d46cd
commit 74a7a550eb
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GPG Key ID: EDABF9711E244EB1
3 changed files with 182 additions and 51 deletions
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2
src/garage/admin.rs
View File

@ -446,7 +446,7 @@ impl AdminRpcHandler {
if opt.detailed {
writeln!(
&mut ret,
" number of blocks: {}",
" number of RC entries (~= number of blocks): {}",
self.garage.block_manager.rc_len()
)
.unwrap();

3
src/garage/cli/structs.rs
View File

@ -8,8 +8,7 @@ pub enum Command {
#[structopt(name = "server")]
Server,
/// Print identifier (public key) of this garage node.
/// Generates a new keypair if necessary.
/// Print identifier (public key) of this Garage node
#[structopt(name = "node-id")]
NodeId(NodeIdOpt),

228
src/model/block.rs
View File

@ -31,10 +31,20 @@ pub const INLINE_THRESHOLD: usize = 3072;
pub const BACKGROUND_WORKERS: u64 = 1;
pub const BACKGROUND_TRANQUILITY: u32 = 3;
const BLOCK_RW_TIMEOUT: Duration = Duration::from_secs(42);
const BLOCK_GC_TIMEOUT: Duration = Duration::from_secs(60);
// Timeout for RPCs that read and write blocks to remote nodes
const BLOCK_RW_TIMEOUT: Duration = Duration::from_secs(30);
// Timeout for RPCs that ask other nodes whether they need a copy
// of a given block before we delete it locally
const NEED_BLOCK_QUERY_TIMEOUT: Duration = Duration::from_secs(5);
const RESYNC_RETRY_TIMEOUT: Duration = Duration::from_secs(10);
// The delay between the time where a resync operation fails
// and the time when it is retried.
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);
/// RPC messages used to share blocks of data between nodes
#[derive(Debug, Serialize, Deserialize)]
@ -180,7 +190,7 @@ impl BlockManager {
/// that are required because of refcount > 0, and will try
/// 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
// 1. Repair blocks from RC table.
let garage = self.garage.load_full().unwrap();
let mut last_hash = None;
for (i, entry) in garage.block_ref_table.data.store.iter().enumerate() {
@ -245,40 +255,51 @@ 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| {
let old_v = old.map(u64_from_be_bytes).unwrap_or(0);
Some(u64::to_be_bytes(old_v + 1).to_vec())
})?;
let old_rc = old_rc.map(u64_from_be_bytes).unwrap_or(0);
if old_rc == 0 {
self.put_to_resync(hash, BLOCK_RW_TIMEOUT)?;
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() {
// 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,
// so in all cases we add the block here to the todo list
// to check later that it arrived correctly, and if not
// we will fecth it from someone.
self.put_to_resync(hash, 2 * BLOCK_RW_TIMEOUT)?;
}
Ok(())
}
/// 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| {
let old_v = old.map(u64_from_be_bytes).unwrap_or(0);
if old_v > 1 {
Some(u64::to_be_bytes(old_v - 1).to_vec())
} else {
None
}
})?;
if new_rc.is_none() {
self.put_to_resync(hash, BLOCK_GC_TIMEOUT)?;
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 {
self.put_to_resync(hash, BLOCK_GC_DELAY + Duration::from_secs(10))?;
}
Ok(())
}
/// Read a block's reference count
pub fn get_block_rc(&self, hash: &Hash) -> Result<u64, Error> {
Ok(self
.rc
.get(hash.as_ref())?
.map(u64_from_be_bytes)
.unwrap_or(0))
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 ----
@ -300,7 +321,7 @@ impl BlockManager {
Ok(f) => f,
Err(e) => {
// Not found but maybe we should have had it ??
self.put_to_resync(hash, Duration::from_millis(0))?;
self.put_to_resync(hash, 2 * BLOCK_RW_TIMEOUT)?;
return Err(Into::into(e));
}
};
@ -314,6 +335,7 @@ impl BlockManager {
.await
.move_block_to_corrupted(hash, self)
.await?;
self.put_to_resync(hash, Duration::from_millis(0))?;
return Err(Error::CorruptData(*hash));
}
@ -328,7 +350,7 @@ impl BlockManager {
.await
.check_block_status(hash, self)
.await?;
Ok(needed && !exists)
Ok(needed.is_nonzero() && !exists)
}
/// Utility: gives the path of the directory in which a block should be found
@ -349,7 +371,7 @@ impl BlockManager {
// ---- Resync loop ----
pub fn spawn_background_worker(self: Arc<Self>) {
// Launch 2 simultaneous workers for background resync loop preprocessing
// Launch n simultaneous workers for background resync loop preprocessing
for i in 0..BACKGROUND_WORKERS {
let bm2 = self.clone();
let background = self.system.background.clone();
@ -407,7 +429,7 @@ impl BlockManager {
let res = self.resync_block(&hash).await;
if let Err(e) = &res {
warn!("Error when resyncing {:?}: {}", hash, e);
self.put_to_resync(&hash, RESYNC_RETRY_TIMEOUT)?;
self.put_to_resync(&hash, RESYNC_RETRY_DELAY)?;
}
Ok(true)
} else {
@ -437,15 +459,18 @@ impl BlockManager {
.check_block_status(hash, self)
.await?;
if exists != needed {
info!(
"Resync block {:?}: exists {}, needed {}",
hash, exists, needed
if exists != needed.is_needed() || exists != needed.is_nonzero() {
debug!(
"Resync block {:?}: exists {}, nonzero rc {}, deletable {}",
hash,
exists,
needed.is_nonzero(),
needed.is_deletable(),
);
}
if exists && !needed {
trace!("Offloading block {:?}", hash);
if exists && needed.is_deletable() {
info!("Resync block {:?}: offloading and deleting", hash);
let mut who = self.replication.write_nodes(hash);
if who.len() < self.replication.write_quorum() {
@ -488,7 +513,7 @@ impl BlockManager {
need_nodes.len()
);
let put_block_message = self.read_block(hash).await.err_context("PutBlock RPC")?;
let put_block_message = self.read_block(hash).await?;
self.system
.rpc
.try_call_many(
@ -499,10 +524,11 @@ impl BlockManager {
.with_quorum(need_nodes.len())
.with_timeout(BLOCK_RW_TIMEOUT),
)
.await?;
.await
.err_context("PutBlock RPC")?;
}
info!(
"Deleting block {:?}, offload finished ({} / {})",
"Deleting unneeded block {:?}, offload finished ({} / {})",
hash,
need_nodes.len(),
who.len()
@ -513,12 +539,16 @@ impl BlockManager {
.await
.delete_if_unneeded(hash, self)
.await?;
self.clear_deleted_block_rc(hash)?;
}
if needed && !exists {
// TODO find a way to not do this if they are sending it to us
// Let's suppose this isn't an issue for now with the BLOCK_RW_TIMEOUT delay
// between the RC being incremented and this part being called.
if needed.is_nonzero() && !exists {
info!(
"Resync block {:?}: fetching absent but needed block (refcount > 0)",
hash
);
let block_data = self.rpc_get_block(hash).await?;
self.write_block(hash, &block_data[..]).await?;
}
@ -526,6 +556,8 @@ impl BlockManager {
Ok(())
}
// ---- Utility: iteration on files in the data directory ----
async fn for_each_file<F, Fut, State>(
&self,
state: State,
@ -608,7 +640,7 @@ impl EndpointHandler<BlockRpc> for BlockManager {
struct BlockStatus {
exists: bool,
needed: bool,
needed: RcEntry,
}
impl BlockManagerLocked {
@ -620,7 +652,7 @@ impl BlockManagerLocked {
let path = mgr.block_path(hash);
let exists = fs::metadata(&path).await.is_ok();
let needed = mgr.get_block_rc(hash)? > 0;
let needed = mgr.get_block_rc(hash)?;
Ok(BlockStatus { exists, needed })
}
@ -659,14 +691,13 @@ impl BlockManagerLocked {
let mut path2 = path.clone();
path2.set_extension("corrupted");
fs::rename(path, path2).await?;
mgr.put_to_resync(hash, Duration::from_millis(0))?;
Ok(())
}
async fn delete_if_unneeded(&self, hash: &Hash, mgr: &BlockManager) -> Result<(), Error> {
let BlockStatus { exists, needed } = self.check_block_status(hash, mgr).await?;
if exists && !needed {
if exists && needed.is_deletable() {
let path = mgr.block_path(hash);
fs::remove_file(path).await?;
}
@ -680,3 +711,104 @@ fn u64_from_be_bytes<T: AsRef<[u8]>>(bytes: T) -> u64 {
x8.copy_from_slice(bytes.as_ref());
u64::from_be_bytes(x8)
}
/// 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()
}
}