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// Copyright Materialize, Inc. and contributors. All rights reserved.
//
// Use of this software is governed by the Business Source License
// included in the LICENSE file.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0.
//! Tokio tasks (and support machinery) for maintaining storage-managed
//! collections.
//!
//! We differentiate between append-only collections and differential
//! collections. The intent is that knowing the type allows being more
//! intentional about what state we keep in memory and how we work when in
//! read-only mode / during zero-downtime upgrades.
//!
//! ## Append-only collections
//!
//! Writers only append blind writes. Those writes never fail. It does not
//! matter at what timestamp they happen (to a degree, but ...).
//!
//! While in read-only mode, the append-only write task can immediately write
//! updates out as batches, but only append them when going out of read-only
//! mode.
//!
//! ## Differential collections
//!
//! These are very similar to the self-correcting persist_sink. We have an
//! in-memory desired state and continually make it so that persist matches
//! desired. As described below (in the task implementation), we could do this
//! in a memory efficient way by keeping open a persist read handle and
//! continually updating/consolidating our desired collection. This way, we
//! would be memory-efficient even in read-only mode.
//!
//! This is an evolution of the current design where, on startup, we bring the
//! persist collection into a known state (mostly by retracting everything) and
//! then assume that this `envd` is the only writer. We panic when that is ever
//! not the case, which we notice when the upper of a collection changes
//! unexpectedly. With this new design we can instead continually update our
//! view of the persist shard and emit updates when needed, when desired
//! changed.
//!
//! NOTE: As it is, we always keep all of desired in memory. Only when told to
//! go out of read-only mode would we start attempting to write.
//!
//! ## Read-only mode
//!
//! When [`CollectionManager`] is in read-only mode it cannot write out to
//! persist. It will, however, maintain the `desired` state of differential
//! collections so that we can immediately start writing out updates when going
//! out of read-only mode.
//!
//! For append-only collections we either panic, in the case of
//! [`CollectionManager::blind_write`], or report back a
//! [`StorageError::ReadOnly`] when trying to append through a
//! [`MonotonicAppender`] returned from
//! [`CollectionManager::monotonic_appender`].
use std::collections::BTreeMap;
use std::ops::ControlFlow;
use std::pin::Pin;
use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::{Arc, Mutex};
use differential_dataflow::consolidation;
use differential_dataflow::lattice::Lattice;
use futures::future::BoxFuture;
use futures::stream::StreamExt;
use futures::{Future, FutureExt};
use mz_ore::now::{EpochMillis, NowFn};
use mz_ore::retry::Retry;
use mz_ore::task::AbortOnDropHandle;
use mz_ore::vec::VecExt;
use mz_persist_client::read::ReadHandle;
use mz_persist_client::write::WriteHandle;
use mz_persist_types::Codec64;
use mz_repr::{Diff, GlobalId, Row, TimestampManipulation};
use mz_storage_client::client::TimestamplessUpdate;
use mz_storage_client::controller::{MonotonicAppender, StorageWriteOp};
use mz_storage_types::controller::InvalidUpper;
use mz_storage_types::parameters::STORAGE_MANAGED_COLLECTIONS_BATCH_DURATION_DEFAULT;
use mz_storage_types::sources::SourceData;
use timely::progress::{Antichain, Timestamp};
use tokio::sync::{mpsc, oneshot, watch};
use tokio::time::{Duration, Instant};
use tracing::{debug, error, info};
use crate::StorageError;
// Default rate at which we advance the uppers of managed collections.
const DEFAULT_TICK_MS: u64 = 1_000;
/// A channel for sending writes to a differential collection.
type DifferentialWriteChannel<T> =
mpsc::UnboundedSender<(StorageWriteOp, oneshot::Sender<Result<(), StorageError<T>>>)>;
/// A channel for sending writes to an append-only collection.
type AppendOnlyWriteChannel<T> = mpsc::UnboundedSender<(
Vec<(Row, Diff)>,
oneshot::Sender<Result<(), StorageError<T>>>,
)>;
type WriteTask = AbortOnDropHandle<()>;
type ShutdownSender = oneshot::Sender<()>;
/// Types of storage-managed/introspection collections:
///
/// Append-only: Only accepts blind writes, writes that can be applied at any
/// timestamp and don’t depend on current collection contents.
///
/// Pseudo append-only: We treat them largely as append-only collections but
/// periodically (currently on bootstrap) retract old updates from them.
///
/// Differential: at any given time `t` , collection contents mirrors some
/// (small cardinality) state. The cardinality of the collection stays constant
/// if the thing that is mirrored doesn’t change in cardinality. At steady
/// state, updates always come in pairs of retractions/additions.
pub enum CollectionManagerKind {
AppendOnly,
Differential,
}
#[derive(Debug, Clone)]
pub struct CollectionManager<T>
where
T: Timestamp + Lattice + Codec64 + TimestampManipulation,
{
/// When a [`CollectionManager`] is in read-only mode it must not affect any
/// changes to external state.
///
/// This is a watch to making sharing this bit with write tasks easier and
/// to allow write tasks to await changes.
pub read_only_rx: watch::Receiver<bool>,
/// Send-side for read-only bit.
pub read_only_tx: Arc<watch::Sender<bool>>,
/// A watch that is always false. This is a hacky workaround for migrating
/// builtin sources in 0dt.
/// TODO(jkosh44) Remove me when persist schema migrations are in.
hacky_always_false_watch: (watch::Sender<bool>, watch::Receiver<bool>),
// WIP: Name TBD! I thought about `managed_collections`, `ivm_collections`,
// `self_correcting_collections`.
/// These are collections that we write to by adding/removing updates to an
/// internal _desired_ collection. The `CollectionManager` continually makes
/// sure that collection contents (in persist) match the desired state.
differential_collections:
Arc<Mutex<BTreeMap<GlobalId, (DifferentialWriteChannel<T>, WriteTask, ShutdownSender)>>>,
/// Collections that we only append to using blind-writes.
///
/// Every write succeeds at _some_ timestamp, and we never check what the
/// actual contents of the collection (in persist) are.
append_only_collections:
Arc<Mutex<BTreeMap<GlobalId, (AppendOnlyWriteChannel<T>, WriteTask, ShutdownSender)>>>,
/// Amount of time we'll wait before sending a batch of inserts to Persist, for user
/// collections.
user_batch_duration_ms: Arc<AtomicU64>,
now: NowFn,
}
/// The `CollectionManager` provides two complementary functions:
/// - Providing an API to append values to a registered set of collections.
/// For this usecase:
/// - The `CollectionManager` expects to be the only writer.
/// - Appending to a closed collection panics
/// - Automatically advancing the timestamp of managed collections every
/// second. For this usecase:
/// - The `CollectionManager` handles contention by permitting and ignoring errors.
/// - Closed collections will not panic if they continue receiving these requests.
impl<T> CollectionManager<T>
where
T: Timestamp + Lattice + Codec64 + From<EpochMillis> + TimestampManipulation,
{
pub(super) fn new(read_only: bool, now: NowFn) -> CollectionManager<T> {
let batch_duration_ms: u64 = STORAGE_MANAGED_COLLECTIONS_BATCH_DURATION_DEFAULT
.as_millis()
.try_into()
.expect("known to fit");
let (read_only_tx, read_only_rx) = watch::channel(read_only);
let (always_false_tx, always_false_rx) = watch::channel(false);
CollectionManager {
read_only_tx: Arc::new(read_only_tx),
read_only_rx,
hacky_always_false_watch: (always_false_tx, always_false_rx),
differential_collections: Arc::new(Mutex::new(BTreeMap::new())),
append_only_collections: Arc::new(Mutex::new(BTreeMap::new())),
user_batch_duration_ms: Arc::new(AtomicU64::new(batch_duration_ms)),
now,
}
}
/// Allow this [`CollectionManager`] to write to external systems, from now
/// on. That is allow it to actually write to collections from now on.
pub fn allow_writes(&mut self) {
self.read_only_tx
.send(false)
.expect("we are holding on to at least one receiver");
}
/// Updates the duration we'll wait to batch events for user owned collections.
pub fn update_user_batch_duration(&self, duration: Duration) {
tracing::info!(?duration, "updating user batch duration");
let millis: u64 = duration.as_millis().try_into().unwrap_or(u64::MAX);
self.user_batch_duration_ms.store(millis, Ordering::Relaxed);
}
/// Registers a new _differential collection_.
///
/// The [CollectionManager] will automatically advance the upper of every
/// registered collection every second.
///
/// Update the `desired` state of a differential collection using
/// [Self::differential_write].
pub(super) fn register_differential_collection<R>(
&self,
id: GlobalId,
write_handle: WriteHandle<SourceData, (), T, Diff>,
read_handle_fn: R,
force_writable: bool,
) where
R: FnMut() -> Pin<Box<dyn Future<Output = ReadHandle<SourceData, (), T, Diff>> + Send>>
+ Send
+ 'static,
{
let mut guard = self
.differential_collections
.lock()
.expect("collection_mgmt panicked");
// Check if this collection is already registered.
if let Some((_writer, task, _shutdown_tx)) = guard.get(&id) {
// The collection is already registered and the task is still running so nothing to do.
if !task.is_finished() {
// TODO(parkmycar): Panic here if we never see this error in production.
tracing::error!("Registered a collection twice! {id:?}");
return;
}
}
let read_only_rx = self.get_read_only_rx(id, force_writable);
// Spawns a new task so we can write to this collection.
let writer_and_handle = DifferentialWriteTask::spawn(
id,
write_handle,
read_handle_fn,
read_only_rx,
self.now.clone(),
);
let prev = guard.insert(id, writer_and_handle);
// Double check the previous task was actually finished.
if let Some((_, prev_task, _)) = prev {
assert!(
prev_task.is_finished(),
"should only spawn a new task if the previous is finished"
);
}
}
/// Registers a new _append-only collection_.
///
/// The [CollectionManager] will automatically advance the upper of every
/// registered collection every second.
pub(super) fn register_append_only_collection(
&self,
id: GlobalId,
write_handle: WriteHandle<SourceData, (), T, Diff>,
force_writable: bool,
) {
let mut guard = self
.append_only_collections
.lock()
.expect("collection_mgmt panicked");
// Check if this collection is already registered.
if let Some((_writer, task, _shutdown_tx)) = guard.get(&id) {
// The collection is already registered and the task is still running so nothing to do.
if !task.is_finished() {
// TODO(parkmycar): Panic here if we never see this error in production.
tracing::error!("Registered a collection twice! {id:?}");
return;
}
}
let read_only_rx = self.get_read_only_rx(id, force_writable);
// Spawns a new task so we can write to this collection.
let writer_and_handle = append_only_write_task(
id,
write_handle,
Arc::clone(&self.user_batch_duration_ms),
self.now.clone(),
read_only_rx,
);
let prev = guard.insert(id, writer_and_handle);
// Double check the previous task was actually finished.
if let Some((_, prev_task, _)) = prev {
assert!(
prev_task.is_finished(),
"should only spawn a new task if the previous is finished"
);
}
}
/// Unregisters the given collection.
///
/// Also waits until the `CollectionManager` has completed all outstanding work to ensure that
/// it has stopped referencing the provided `id`.
#[mz_ore::instrument(level = "debug")]
pub(super) fn unregister_collection(&self, id: GlobalId) -> BoxFuture<'static, ()> {
let prev = self
.differential_collections
.lock()
.expect("CollectionManager panicked")
.remove(&id);
// Wait for the task to complete before reporting as unregisted.
if let Some((_prev_writer, prev_task, shutdown_tx)) = prev {
// Notify the task it needs to shutdown.
//
// We can ignore errors here because they indicate the task is already done.
let _ = shutdown_tx.send(());
return Box::pin(prev_task.map(|_| ()));
}
let prev = self
.append_only_collections
.lock()
.expect("CollectionManager panicked")
.remove(&id);
// Wait for the task to complete before reporting as unregisted.
if let Some((_prev_writer, prev_task, shutdown_tx)) = prev {
// Notify the task it needs to shutdown.
//
// We can ignore errors here because they indicate the task is already done.
let _ = shutdown_tx.send(());
return Box::pin(prev_task.map(|_| ()));
}
Box::pin(futures::future::ready(()))
}
/// Appends `updates` to the append-only collection identified by `id`, at
/// _some_ timestamp. Does not wait for the append to complete.
///
/// # Panics
/// - If `id` does not belong to an append-only collections.
/// - If this [`CollectionManager`] is in read-only mode.
/// - If the collection closed.
pub(super) fn blind_write(&self, id: GlobalId, updates: Vec<(Row, Diff)>) {
if *self.read_only_rx.borrow() {
panic!("attempting blind write to {} while in read-only mode", id);
}
if !updates.is_empty() {
// Get the update channel in a block to make sure the Mutex lock is scoped.
let update_tx = {
let guard = self
.append_only_collections
.lock()
.expect("CollectionManager panicked");
let (update_tx, _, _) = guard.get(&id).expect("missing append-only collection");
update_tx.clone()
};
let (tx, _rx) = oneshot::channel();
update_tx.send((updates, tx)).expect("rx hung up");
}
}
/// Updates the desired collection state of the differential collection identified by
/// `id`. The underlying persist shard will reflect this change at
/// _some_point. Does not wait for the change to complete.
///
/// # Panics
/// - If `id` does not belong to a differential collection.
/// - If the collection closed.
pub(super) fn differential_write(&self, id: GlobalId, op: StorageWriteOp) {
if !op.is_empty_append() {
// Get the update channel in a block to make sure the Mutex lock is scoped.
let update_tx = {
let guard = self
.differential_collections
.lock()
.expect("CollectionManager panicked");
let (update_tx, _, _) = guard.get(&id).expect("missing differential collection");
update_tx.clone()
};
let (tx, _rx) = oneshot::channel();
update_tx.send((op, tx)).expect("rx hung up");
}
}
/// Appends the given `updates` to the differential collection identified by `id`.
///
/// # Panics
/// - If `id` does not belong to a differential collection.
/// - If the collection closed.
pub(super) fn differential_append(&self, id: GlobalId, updates: Vec<(Row, Diff)>) {
self.differential_write(id, StorageWriteOp::Append { updates })
}
/// Returns a [`MonotonicAppender`] that can be used to monotonically append updates to the
/// collection correlated with `id`.
pub(super) fn monotonic_appender(
&self,
id: GlobalId,
) -> Result<MonotonicAppender<T>, StorageError<T>> {
let guard = self
.append_only_collections
.lock()
.expect("CollectionManager panicked");
let tx = guard
.get(&id)
.map(|(tx, _, _)| tx.clone())
.ok_or(StorageError::IdentifierMissing(id))?;
Ok(MonotonicAppender::new(tx))
}
fn get_read_only_rx(&self, id: GlobalId, force_writable: bool) -> watch::Receiver<bool> {
if force_writable {
assert!(id.is_system(), "unexpected non-system global id: {id:?}");
self.hacky_always_false_watch.1.clone()
} else {
self.read_only_rx.clone()
}
}
}
/// A task that will make it so that the state in persist matches the desired
/// state and continuously bump the upper for the specified collection.
///
/// NOTE: This implementation is a bit clunky, and could be optimized by not keeping
/// all of desired in memory (see commend below). It is meant to showcase the
/// general approach.
struct DifferentialWriteTask<T, R>
where
T: Timestamp + Lattice + Codec64 + From<EpochMillis> + TimestampManipulation,
R: FnMut() -> Pin<Box<dyn Future<Output = ReadHandle<SourceData, (), T, Diff>> + Send>>
+ Send
+ 'static,
{
/// The collection that we are writing to.
id: GlobalId,
write_handle: WriteHandle<SourceData, (), T, Diff>,
/// For getting a [`ReadHandle`] to sync our state to persist contents.
read_handle_fn: R,
read_only_watch: watch::Receiver<bool>,
// Keep track of the read-only bit in our own state. Also so that we can
// assert that we don't flip back from read-write to read-only.
read_only: bool,
now: NowFn,
/// In the absence of updates, we regularly bump the upper to "now", on this
/// interval. This makes it so the collection remains readable at recent
/// timestamps.
upper_tick_interval: tokio::time::Interval,
/// Receiver for write commands. These change our desired state.
cmd_rx: mpsc::UnboundedReceiver<(StorageWriteOp, oneshot::Sender<Result<(), StorageError<T>>>)>,
/// We have to shut down when receiving from this.
shutdown_rx: oneshot::Receiver<()>,
/// The contents of the collection as it should be according to whoever is
/// driving us around.
// This is memory inefficient: we always keep a full copy of
// desired, so that we can re-derive a to_write if/when someone else
// writes to persist and we notice because of an upper conflict.
// This is optimized for the case where we rarely have more than one
// writer.
//
// We can optimize for a multi-writer case by keeping an open
// ReadHandle and continually reading updates from persist, updating
// a desired in place. Similar to the self-correcting persist_sink.
desired: Vec<(Row, i64)>,
/// Updates that we have to write when next writing to persist. This is
/// determined by looking at what is desired and what is in persist.
to_write: Vec<(Row, i64)>,
/// Current upper of the persist shard. We keep track of this so that we
/// realize when someone else writes to the shard, in which case we have to
/// update our state of the world, that is update our `to_write` based on
/// `desired` and the contents of the persist shard.
current_upper: T,
}
impl<T, R> DifferentialWriteTask<T, R>
where
T: Timestamp + Lattice + Codec64 + From<EpochMillis> + TimestampManipulation,
R: FnMut() -> Pin<Box<dyn Future<Output = ReadHandle<SourceData, (), T, Diff>> + Send>>
+ Send
+ 'static,
{
/// Spawns a [`DifferentialWriteTask`] in an [`mz_ore::task`] and returns
/// handles for interacting with it.
fn spawn(
id: GlobalId,
write_handle: WriteHandle<SourceData, (), T, Diff>,
read_handle_fn: R,
read_only_watch: watch::Receiver<bool>,
now: NowFn,
) -> (DifferentialWriteChannel<T>, WriteTask, ShutdownSender) {
let (tx, rx) = mpsc::unbounded_channel();
let (shutdown_tx, shutdown_rx) = oneshot::channel();
let upper_tick_interval = tokio::time::interval(Duration::from_millis(DEFAULT_TICK_MS));
let current_upper = T::minimum();
let read_only = *read_only_watch.borrow();
let task = Self {
id,
write_handle,
read_handle_fn,
read_only_watch,
read_only,
now,
upper_tick_interval,
cmd_rx: rx,
shutdown_rx,
desired: Vec::new(),
to_write: Vec::new(),
current_upper,
};
let handle = mz_ore::task::spawn(
|| format!("CollectionManager-differential_write_task-{id}"),
async move {
let res = task.run().await;
match res {
ControlFlow::Break(reason) => {
info!("write_task-{} ending: {}", id, reason);
}
c => {
unreachable!(
"cannot break out of the loop with a Continue, but got: {:?}",
c
);
}
}
},
);
(tx, handle.abort_on_drop(), shutdown_tx)
}
async fn run(mut self) -> ControlFlow<String> {
const BATCH_SIZE: usize = 4096;
let mut updates = Vec::with_capacity(BATCH_SIZE);
loop {
tokio::select! {
// Prefer sending actual updates over just bumping the upper,
// because sending updates also bump the upper.
biased;
// Listen for a shutdown signal so we can gracefully cleanup.
_ = &mut self.shutdown_rx => {
self.handle_shutdown();
return ControlFlow::Break("graceful shutdown".to_string());
}
// Pull a chunk of queued updates off the channel.
count = self.cmd_rx.recv_many(&mut updates, BATCH_SIZE) => {
if count > 0 {
let _ = self.handle_updates(&mut updates).await?;
} else {
// Sender has been dropped, which means the collection
// should have been unregistered, break out of the run
// loop if we weren't already aborted.
return ControlFlow::Break("sender has been dropped".to_string());
}
}
_it_changed = self.read_only_watch.changed() => {
assert!(!*self.read_only_watch.borrow(), "can only switch from read-only to read-write");
self.read_only = false;
// We can now write, attempt to do that right away, even if
// our `to_write` is empty. This way, we might learn that
// there is something in persist that we have to retract.
let _ = self.write_to_persist(vec![]).await?;
}
// If we haven't received any updates, then we'll move the upper forward.
_ = self.upper_tick_interval.tick() => {
if self.read_only {
// Not bumping uppers while in read-only mode.
continue;
}
let _ = self.tick_upper().await?;
},
}
}
}
async fn tick_upper(&mut self) -> ControlFlow<String> {
let now = T::from((self.now)());
if now <= self.current_upper {
// Upper is already further along than current wall-clock time, no
// need to bump it.
return ControlFlow::Continue(());
}
assert!(!self.read_only);
let res = self
.write_handle
.compare_and_append_batch(
&mut [],
Antichain::from_elem(self.current_upper.clone()),
Antichain::from_elem(now.clone()),
)
.await
.expect("valid usage");
match res {
// All good!
Ok(()) => {
tracing::debug!(%self.id, "bumped upper of differential collection");
self.current_upper = now;
}
Err(err) => {
// Someone else wrote to the collection or bumped the upper. We
// need to sync to latest persist state and potentially patch up
// our `to_write`, based on what we learn and `desired`.
let actual_upper = if let Some(ts) = err.current.as_option() {
ts.clone()
} else {
return ControlFlow::Break("upper is the empty antichain".to_string());
};
tracing::info!(%self.id, ?actual_upper, expected_upper = ?self.current_upper, "upper mismatch while bumping upper, syncing to persist state");
self.current_upper = actual_upper;
self.sync_to_persist().await;
}
}
ControlFlow::Continue(())
}
fn handle_shutdown(&mut self) {
let mut senders = Vec::new();
// Prevent new messages from being sent.
self.cmd_rx.close();
// Get as many waiting senders as possible.
while let Ok((_batch, sender)) = self.cmd_rx.try_recv() {
senders.push(sender);
}
// Notify them that this collection is closed.
//
// Note: if a task is shutting down, that indicates the source has been
// dropped, at which point the identifier is invalid. Returning this
// error provides a better user experience.
notify_listeners(senders, || Err(StorageError::IdentifierInvalid(self.id)));
}
async fn handle_updates(
&mut self,
batch: &mut Vec<(StorageWriteOp, oneshot::Sender<Result<(), StorageError<T>>>)>,
) -> ControlFlow<String> {
// Put in place _some_ rate limiting.
let batch_duration_ms = STORAGE_MANAGED_COLLECTIONS_BATCH_DURATION_DEFAULT;
let use_batch_now = Instant::now();
let min_time_to_complete = use_batch_now + batch_duration_ms;
tracing::debug!(
?use_batch_now,
?batch_duration_ms,
?min_time_to_complete,
"batch duration",
);
let mut responders = Vec::with_capacity(batch.len());
for (op, tx) in batch.drain(..) {
self.apply_write_op(op);
responders.push(tx);
}
// TODO: Maybe don't do it every time?
consolidation::consolidate(&mut self.desired);
consolidation::consolidate(&mut self.to_write);
// Reset the interval which is used to periodically bump the uppers
// because the uppers will get bumped with the following update.
// This makes it such that we will write at most once every
// `interval`.
//
// For example, let's say our `DEFAULT_TICK` interval is 10, so at
// `t + 10`, `t + 20`, ... we'll bump the uppers. If we receive an
// update at `t + 3` we want to shift this window so we bump the
// uppers at `t + 13`, `t + 23`, ... which resetting the interval
// accomplishes.
self.upper_tick_interval.reset();
self.write_to_persist(responders).await?;
// Wait until our artificial latency has completed.
//
// Note: if writing to persist took longer than `DEFAULT_TICK` this
// await will resolve immediately.
tokio::time::sleep_until(min_time_to_complete).await;
ControlFlow::Continue(())
}
/// Apply the given write operation to the `desired`/`to_write` state.
fn apply_write_op(&mut self, op: StorageWriteOp) {
match op {
StorageWriteOp::Append { updates } => {
self.desired.extend_from_slice(&updates);
self.to_write.extend(updates);
}
StorageWriteOp::Delete { filter } => {
let to_delete = self.desired.drain_filter_swapping(|(row, _)| filter(row));
let retractions = to_delete.map(|(row, diff)| (row, -diff));
self.to_write.extend(retractions);
}
}
}
/// Attempt to write what is currently in [Self::to_write] to persist,
/// retrying and re-syncing to persist when necessary, that is when the
/// upper was not what we expected.
async fn write_to_persist(
&mut self,
responders: Vec<oneshot::Sender<Result<(), StorageError<T>>>>,
) -> ControlFlow<String> {
if self.read_only {
tracing::debug!(%self.id, "not writing to differential collection: read-only");
// Not attempting to write while in read-only mode.
return ControlFlow::Continue(());
}
// We'll try really hard to succeed, but eventually stop.
//
// Note: it's very rare we should ever need to retry, and if we need to
// retry it should only take 1 or 2 attempts. We set `max_tries` to be
// high though because if we hit some edge case we want to try hard to
// commit the data.
let retries = Retry::default()
.initial_backoff(Duration::from_secs(1))
.clamp_backoff(Duration::from_secs(3))
.factor(1.25)
.max_tries(20)
.into_retry_stream();
let mut retries = Box::pin(retries);
loop {
// Append updates to persist!
let now = T::from((self.now)());
let new_upper = std::cmp::max(
now,
TimestampManipulation::step_forward(&self.current_upper),
);
let updates_to_write = self
.to_write
.iter()
.map(|(row, diff)| {
(
(SourceData(Ok(row.clone())), ()),
self.current_upper.clone(),
diff.clone(),
)
})
.collect::<Vec<_>>();
assert!(!self.read_only);
let res = self
.write_handle
.compare_and_append(
updates_to_write,
Antichain::from_elem(self.current_upper.clone()),
Antichain::from_elem(new_upper.clone()),
)
.await
.expect("valid usage");
match res {
// Everything was successful!
Ok(()) => {
// Notify all of our listeners.
notify_listeners(responders, || Ok(()));
self.current_upper = new_upper;
// Very important! This is empty at steady state, while
// desired keeps an in-memory copy of desired state.
self.to_write.clear();
tracing::debug!(%self.id, "appended to differential collection");
// Break out of the retry loop so we can wait for more data.
break;
}
// Failed to write to some collections,
Err(err) => {
// Someone else wrote to the collection. We need to read
// from persist and update to_write based on that and the
// desired state.
let actual_upper = if let Some(ts) = err.current.as_option() {
ts.clone()
} else {
return ControlFlow::Break("upper is the empty antichain".to_string());
};
tracing::info!(%self.id, ?actual_upper, expected_upper = ?self.current_upper, "retrying append for differential collection");
// We've exhausted all of our retries, notify listeners and
// break out of the retry loop so we can wait for more data.
if retries.next().await.is_none() {
let invalid_upper = InvalidUpper {
id: self.id,
current_upper: err.current,
};
notify_listeners(responders, || {
Err(StorageError::InvalidUppers(vec![invalid_upper.clone()]))
});
error!(
"exhausted retries when appending to managed collection {}",
self.id
);
break;
}
self.current_upper = actual_upper;
self.sync_to_persist().await;
debug!("Retrying invalid-uppers error while appending to differential collection {}", self.id);
}
}
}
ControlFlow::Continue(())
}
/// Re-derives [Self::to_write] by looking at [Self::desired] and the
/// current state in persist. We want to insert everything in desired and
/// retract everything in persist. But ideally most of that cancels out in
/// consolidation.
///
/// To be called when a `compare_and_append` failed because the upper didn't
/// match what we expected.
async fn sync_to_persist(&mut self) {
let mut read_handle = (self.read_handle_fn)().await;
let as_of = self
.current_upper
.step_back()
.unwrap_or_else(|| T::minimum());
let as_of = Antichain::from_elem(as_of);
let snapshot = read_handle.snapshot_and_fetch(as_of).await;
let mut negated_oks = match snapshot {
Ok(contents) => {
let mut snapshot = Vec::with_capacity(contents.len());
for ((data, _), _, diff) in contents {
let row = data.expect("invalid protobuf data").0.unwrap();
snapshot.push((row, -diff));
}
snapshot
}
Err(_) => panic!("read before since"),
};
self.to_write.clear();
self.to_write.extend(self.desired.iter().cloned());
self.to_write.append(&mut negated_oks);
consolidation::consolidate(&mut self.to_write);
}
}
/// Spawns an [`mz_ore::task`] that will continuously bump the upper for the specified collection,
/// and append data that is sent via the provided [`mpsc::UnboundedSender`].
///
/// TODO(parkmycar): One day if we want to customize the tick interval for each collection, that
/// should be done here.
/// TODO(parkmycar): Maybe add prometheus metrics for each collection?
fn append_only_write_task<T>(
id: GlobalId,
mut write_handle: WriteHandle<SourceData, (), T, Diff>,
user_batch_duration_ms: Arc<AtomicU64>,
now: NowFn,
read_only: watch::Receiver<bool>,
) -> (AppendOnlyWriteChannel<T>, WriteTask, ShutdownSender)
where
T: Timestamp + Lattice + Codec64 + From<EpochMillis> + TimestampManipulation,
{
let (tx, mut rx) = mpsc::unbounded_channel();
let (shutdown_tx, mut shutdown_rx) = oneshot::channel();
let handle = mz_ore::task::spawn(
|| format!("CollectionManager-append_only_write_task-{id}"),
async move {
let mut interval = tokio::time::interval(Duration::from_millis(DEFAULT_TICK_MS));
const BATCH_SIZE: usize = 4096;
let mut batch: Vec<(Vec<_>, _)> = Vec::with_capacity(BATCH_SIZE);
'run: loop {
tokio::select! {
// Prefer sending actual updates over just bumping the upper, because sending
// updates also bump the upper.
biased;
// Listen for a shutdown signal so we can gracefully cleanup.
_ = &mut shutdown_rx => {
let mut senders = Vec::new();
// Prevent new messages from being sent.
rx.close();
// Get as many waiting senders as possible.
while let Ok((_batch, sender)) = rx.try_recv() {
senders.push(sender);
}
// Notify them that this collection is closed.
//
// Note: if a task is shutting down, that indicates the source has been
// dropped, at which point the identifier is invalid. Returning this
// error provides a better user experience.
notify_listeners(senders, || Err(StorageError::IdentifierInvalid(id)));
break 'run;
}
// Pull a chunk of queued updates off the channel.
count = rx.recv_many(&mut batch, BATCH_SIZE) => {
if count > 0 {
// To rate limit appends to persist we add artificial latency, and will
// finish no sooner than this instant.
let batch_duration_ms = match id {
GlobalId::User(_) => Duration::from_millis(user_batch_duration_ms.load(Ordering::Relaxed)),
// For non-user collections, always just use the default.
_ => STORAGE_MANAGED_COLLECTIONS_BATCH_DURATION_DEFAULT,
};
let use_batch_now = Instant::now();
let min_time_to_complete = use_batch_now + batch_duration_ms;
tracing::debug!(
?use_batch_now,
?batch_duration_ms,
?min_time_to_complete,
"batch duration",
);
// Reset the interval which is used to periodically bump the uppers
// because the uppers will get bumped with the following update. This
// makes it such that we will write at most once every `interval`.
//
// For example, let's say our `DEFAULT_TICK` interval is 10, so at
// `t + 10`, `t + 20`, ... we'll bump the uppers. If we receive an
// update at `t + 3` we want to shift this window so we bump the uppers
// at `t + 13`, `t + 23`, ... which reseting the interval accomplishes.
interval.reset();
let mut all_rows = Vec::with_capacity(batch.iter().map(|(rows, _)| rows.len()).sum());
let mut responders = Vec::with_capacity(batch.len());
for (rows, reponders) in batch.drain(..) {
all_rows.extend(rows.into_iter().map(|(row, diff)| TimestamplessUpdate { row, diff}));
responders.push(reponders);
}
if *read_only.borrow() {
tracing::warn!(%id, ?all_rows, "append while in read-only mode");
notify_listeners(responders, || Err(StorageError::ReadOnly));
continue;
}
// Append updates to persist!
let at_least = T::from(now());
monotonic_append(&mut write_handle, all_rows, at_least).await;
// Notify all of our listeners.
notify_listeners(responders, || Ok(()));
// Wait until our artificial latency has completed.
//
// Note: if writing to persist took longer than `DEFAULT_TICK` this
// await will resolve immediately.
tokio::time::sleep_until(min_time_to_complete).await;
} else {
// Sender has been dropped, which means the collection should have been
// unregistered, break out of the run loop if we weren't already
// aborted.
break 'run;
}
}
// If we haven't received any updates, then we'll move the upper forward.
_ = interval.tick() => {
if *read_only.borrow() {
// Not bumping uppers while in read-only mode.
continue;
}
// Update our collection.
let now = T::from(now());
let updates = vec![];
let at_least = now.clone();
// Failures don't matter when advancing collections' uppers. This might
// fail when a clusterd happens to be writing to this concurrently.
// Advancing uppers here is best-effort and only needs to succeed if no
// one else is advancing it; contention proves otherwise.
monotonic_append(&mut write_handle, updates, at_least).await;
},
}
}
info!("write_task-{id} ending");
},
);
(tx, handle.abort_on_drop(), shutdown_tx)
}
async fn monotonic_append<T: Timestamp + Lattice + Codec64 + TimestampManipulation>(
write_handle: &mut WriteHandle<SourceData, (), T, Diff>,
updates: Vec<TimestamplessUpdate>,
at_least: T,
) {
let mut expected_upper = write_handle.shared_upper();
loop {
if updates.is_empty() && expected_upper.is_empty() {
// Ignore timestamp advancement for
// closed collections. TODO? Make this a
// correctable error
return;
}
let upper = expected_upper
.into_option()
.expect("cannot append data to closed collection");
let lower = if upper.less_than(&at_least) {
at_least.clone()
} else {
upper.clone()
};
let new_upper = TimestampManipulation::step_forward(&lower);
let updates = updates
.iter()
.map(|TimestamplessUpdate { row, diff }| {
((SourceData(Ok(row.clone())), ()), lower.clone(), diff)
})
.collect::<Vec<_>>();
let res = write_handle
.compare_and_append(
updates,
Antichain::from_elem(upper),
Antichain::from_elem(new_upper),
)
.await
.expect("valid usage");
match res {
Ok(()) => return,
Err(err) => {
expected_upper = err.current;
continue;
}
}
}
}
// Helper method for notifying listeners.
fn notify_listeners<T>(
responders: impl IntoIterator<Item = oneshot::Sender<T>>,
result: impl Fn() -> T,
) {
for r in responders {
// We don't care if the listener disappeared.
let _ = r.send(result());
}
}