mz_persist_client/read.rs
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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.
//! Read capabilities and handles
use async_stream::stream;
use std::backtrace::Backtrace;
use std::collections::BTreeMap;
use std::fmt::Debug;
use std::future::Future;
use std::sync::Arc;
use std::time::Duration;
use differential_dataflow::consolidation::consolidate_updates;
use differential_dataflow::difference::Semigroup;
use differential_dataflow::lattice::Lattice;
use differential_dataflow::trace::Description;
use futures::Stream;
use futures_util::{stream, StreamExt};
use itertools::Either;
use mz_dyncfg::Config;
use mz_ore::instrument;
use mz_ore::now::EpochMillis;
use mz_ore::task::{AbortOnDropHandle, JoinHandle, RuntimeExt};
use mz_persist::location::{Blob, SeqNo};
use mz_persist_types::columnar::{ColumnDecoder, Schema2};
use mz_persist_types::{Codec, Codec64};
use proptest_derive::Arbitrary;
use serde::{Deserialize, Serialize};
use timely::progress::{Antichain, Timestamp};
use timely::PartialOrder;
use tokio::runtime::Handle;
use tracing::{debug_span, warn, Instrument};
use uuid::Uuid;
use crate::batch::{BLOB_TARGET_SIZE, STRUCTURED_ORDER, STRUCTURED_ORDER_UNTIL_SHARD};
use crate::cfg::RetryParameters;
use crate::fetch::{fetch_leased_part, FetchBatchFilter, FetchedPart, Lease, LeasedBatchPart};
use crate::internal::encoding::Schemas;
use crate::internal::machine::{ExpireFn, Machine};
use crate::internal::metrics::Metrics;
use crate::internal::state::{BatchPart, HollowBatch};
use crate::internal::watch::StateWatch;
use crate::iter::{CodecSort, Consolidator, StructuredSort};
use crate::schema::SchemaCache;
use crate::stats::{SnapshotPartStats, SnapshotPartsStats, SnapshotStats};
use crate::{parse_id, GarbageCollector, PersistConfig, ShardId};
pub use crate::internal::encoding::LazyPartStats;
pub use crate::internal::state::Since;
/// An opaque identifier for a reader of a persist durable TVC (aka shard).
#[derive(Arbitrary, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
#[serde(try_from = "String", into = "String")]
pub struct LeasedReaderId(pub(crate) [u8; 16]);
impl std::fmt::Display for LeasedReaderId {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(f, "r{}", Uuid::from_bytes(self.0))
}
}
impl std::fmt::Debug for LeasedReaderId {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(f, "LeasedReaderId({})", Uuid::from_bytes(self.0))
}
}
impl std::str::FromStr for LeasedReaderId {
type Err = String;
fn from_str(s: &str) -> Result<Self, Self::Err> {
parse_id('r', "LeasedReaderId", s).map(LeasedReaderId)
}
}
impl From<LeasedReaderId> for String {
fn from(reader_id: LeasedReaderId) -> Self {
reader_id.to_string()
}
}
impl TryFrom<String> for LeasedReaderId {
type Error = String;
fn try_from(s: String) -> Result<Self, Self::Error> {
s.parse()
}
}
impl LeasedReaderId {
pub(crate) fn new() -> Self {
LeasedReaderId(*Uuid::new_v4().as_bytes())
}
}
/// Capable of generating a snapshot of all data at `as_of`, followed by a
/// listen of all updates.
///
/// For more details, see [`ReadHandle::snapshot`] and [`Listen`].
#[derive(Debug)]
pub struct Subscribe<K: Codec, V: Codec, T, D> {
snapshot: Option<Vec<LeasedBatchPart<T>>>,
listen: Listen<K, V, T, D>,
}
impl<K, V, T, D> Subscribe<K, V, T, D>
where
K: Debug + Codec,
V: Debug + Codec,
T: Timestamp + Lattice + Codec64,
D: Semigroup + Codec64 + Send + Sync,
{
fn new(snapshot_parts: Vec<LeasedBatchPart<T>>, listen: Listen<K, V, T, D>) -> Self {
Subscribe {
snapshot: Some(snapshot_parts),
listen,
}
}
/// Returns a `LeasedBatchPart` enriched with the proper metadata.
///
/// First returns snapshot parts, until they're exhausted, at which point
/// begins returning listen parts.
///
/// The returned `Antichain` represents the subscription progress as it will
/// be _after_ the returned parts are fetched.
#[instrument(level = "debug", fields(shard = %self.listen.handle.machine.shard_id()))]
pub async fn next(
&mut self,
// If Some, an override for the default listen sleep retry parameters.
listen_retry: Option<RetryParameters>,
) -> Vec<ListenEvent<T, LeasedBatchPart<T>>> {
match self.snapshot.take() {
Some(parts) => vec![ListenEvent::Updates(parts)],
None => {
let (parts, upper) = self.listen.next(listen_retry).await;
vec![ListenEvent::Updates(parts), ListenEvent::Progress(upper)]
}
}
}
}
impl<K, V, T, D> Subscribe<K, V, T, D>
where
K: Debug + Codec,
V: Debug + Codec,
T: Timestamp + Lattice + Codec64,
D: Semigroup + Codec64 + Send + Sync,
{
/// Equivalent to `next`, but rather than returning a [`LeasedBatchPart`],
/// fetches and returns the data from within it.
#[instrument(level = "debug", fields(shard = %self.listen.handle.machine.shard_id()))]
pub async fn fetch_next(
&mut self,
) -> Vec<ListenEvent<T, ((Result<K, String>, Result<V, String>), T, D)>> {
let events = self.next(None).await;
let new_len = events
.iter()
.map(|event| match event {
ListenEvent::Updates(parts) => parts.len(),
ListenEvent::Progress(_) => 1,
})
.sum();
let mut ret = Vec::with_capacity(new_len);
for event in events {
match event {
ListenEvent::Updates(parts) => {
for part in parts {
let fetched_part = self.listen.fetch_batch_part(part).await;
let updates = fetched_part.collect::<Vec<_>>();
if !updates.is_empty() {
ret.push(ListenEvent::Updates(updates));
}
}
}
ListenEvent::Progress(progress) => ret.push(ListenEvent::Progress(progress)),
}
}
ret
}
/// Fetches the contents of `part` and returns its lease.
pub async fn fetch_batch_part(&mut self, part: LeasedBatchPart<T>) -> FetchedPart<K, V, T, D> {
self.listen.fetch_batch_part(part).await
}
}
impl<K, V, T, D> Subscribe<K, V, T, D>
where
K: Debug + Codec,
V: Debug + Codec,
T: Timestamp + Lattice + Codec64,
D: Semigroup + Codec64 + Send + Sync,
{
/// Politely expires this subscribe, releasing its lease.
///
/// There is a best-effort impl in Drop for [`ReadHandle`] to expire the
/// [`ReadHandle`] held by the subscribe that wasn't explicitly expired
/// with this method. When possible, explicit expiry is still preferred
/// because the Drop one is best effort and is dependant on a tokio
/// [Handle] being available in the TLC at the time of drop (which is a bit
/// subtle). Also, explicit expiry allows for control over when it happens.
pub async fn expire(mut self) {
let _ = self.snapshot.take(); // Drop all leased parts.
self.listen.expire().await;
}
}
/// Data and progress events of a shard subscription.
///
/// TODO: Unify this with [timely::dataflow::operators::capture::event::Event].
#[derive(Debug, PartialEq)]
pub enum ListenEvent<T, D> {
/// Progress of the shard.
Progress(Antichain<T>),
/// Data of the shard.
Updates(Vec<D>),
}
/// An ongoing subscription of updates to a shard.
#[derive(Debug)]
pub struct Listen<K: Codec, V: Codec, T, D> {
handle: ReadHandle<K, V, T, D>,
watch: StateWatch<K, V, T, D>,
as_of: Antichain<T>,
since: Antichain<T>,
frontier: Antichain<T>,
}
impl<K, V, T, D> Listen<K, V, T, D>
where
K: Debug + Codec,
V: Debug + Codec,
T: Timestamp + Lattice + Codec64,
D: Semigroup + Codec64 + Send + Sync,
{
async fn new(mut handle: ReadHandle<K, V, T, D>, as_of: Antichain<T>) -> Self {
let since = as_of.clone();
// This listen only needs to distinguish things after its frontier
// (initially as_of although the frontier is inclusive and the as_of
// isn't). Be a good citizen and downgrade early.
handle.downgrade_since(&since).await;
let watch = handle.machine.applier.watch();
Listen {
handle,
watch,
since,
frontier: as_of.clone(),
as_of,
}
}
/// An exclusive upper bound on the progress of this Listen.
pub fn frontier(&self) -> &Antichain<T> {
&self.frontier
}
/// Attempt to pull out the next values of this subscription.
///
/// The returned [`LeasedBatchPart`] is appropriate to use with
/// `crate::fetch::fetch_leased_part`.
///
/// The returned `Antichain` represents the subscription progress as it will
/// be _after_ the returned parts are fetched.
pub async fn next(
&mut self,
// If Some, an override for the default listen sleep retry parameters.
retry: Option<RetryParameters>,
) -> (Vec<LeasedBatchPart<T>>, Antichain<T>) {
let batch = self
.handle
.machine
.next_listen_batch(
&self.frontier,
&mut self.watch,
Some(&self.handle.reader_id),
retry,
)
.await;
// A lot of things across mz have to line up to hold the following
// invariant and violations only show up as subtle correctness errors,
// so explictly validate it here. Better to panic and roll back a
// release than be incorrect (also potentially corrupting a sink).
//
// Note that the since check is intentionally less_than, not less_equal.
// If a batch's since is X, that means we can no longer distinguish X
// (beyond self.frontier) from X-1 (not beyond self.frontier) to keep
// former and filter out the latter.
assert!(
PartialOrder::less_than(batch.desc.since(), &self.frontier)
// Special case when the frontier == the as_of (i.e. the first
// time this is called on a new Listen). Because as_of is
// _exclusive_, we don't need to be able to distinguish X from
// X-1.
|| (self.frontier == self.as_of
&& PartialOrder::less_equal(batch.desc.since(), &self.frontier)),
"Listen on {} received a batch {:?} advanced past the listen frontier {:?}",
self.handle.machine.shard_id(),
batch.desc,
self.frontier
);
let new_frontier = batch.desc.upper().clone();
// We will have a new frontier, so this is an opportunity to downgrade our
// since capability. Go through `maybe_heartbeat` so we can rate limit
// this along with our heartbeats.
//
// HACK! Everything would be simpler if we could downgrade since to the
// new frontier, but we can't. The next call needs to be able to
// distinguish between the times T at the frontier (to emit updates with
// these times) and T-1 (to filter them). Advancing the since to
// frontier would erase the ability to distinguish between them. Ideally
// we'd use what is conceptually "batch.upper - 1" (the greatest
// elements that are still strictly less than batch.upper, which will be
// the new value of self.frontier after this call returns), but the
// trait bounds on T don't give us a way to compute that directly.
// Instead, we sniff out any elements in self.frontier (the upper of the
// batch the last time we called this) that are strictly less_than the
// batch upper to compute a new since. For totally ordered times
// (currently always the case in mz) self.frontier will always have a
// single element and it will be less_than upper, but the following
// logic is (hopefully) correct for partially order times as well. We
// could also abuse the fact that every time we actually emit is
// guaranteed by definition to be less_than upper to be a bit more
// prompt, but this would involve a lot more temporary antichains and
// it's unclear if that's worth it.
for x in self.frontier.elements().iter() {
let less_than_upper = batch.desc.upper().elements().iter().any(|u| x.less_than(u));
if less_than_upper {
self.since.join_assign(&Antichain::from_elem(x.clone()));
}
}
// IMPORTANT! Make sure this `lease_batch_parts` stays before the
// `maybe_downgrade_since` call. Otherwise, we might give up our
// capability on the batch's SeqNo before we lease it, which could lead
// to blobs that it references being GC'd.
let filter = FetchBatchFilter::Listen {
as_of: self.as_of.clone(),
lower: self.frontier.clone(),
};
let parts = self.handle.lease_batch_parts(batch, filter).collect().await;
self.handle.maybe_downgrade_since(&self.since).await;
// NB: Keep this after we use self.frontier to join_assign self.since
// and also after we construct metadata.
self.frontier = new_frontier;
(parts, self.frontier.clone())
}
}
impl<K, V, T, D> Listen<K, V, T, D>
where
K: Debug + Codec,
V: Debug + Codec,
T: Timestamp + Lattice + Codec64,
D: Semigroup + Codec64 + Send + Sync,
{
/// Attempt to pull out the next values of this subscription.
///
/// The updates received in [ListenEvent::Updates] should be assumed to be in arbitrary order
/// and not necessarily consolidated. However, the timestamp of each individual update will be
/// greater than or equal to the last received [ListenEvent::Progress] frontier (or this
/// [Listen]'s initial `as_of` frontier if no progress event has been emitted yet) and less
/// than the next [ListenEvent::Progress] frontier.
///
/// If you have a use for consolidated listen output, given that snapshots can't be
/// consolidated, come talk to us!
#[instrument(level = "debug", name = "listen::next", fields(shard = %self.handle.machine.shard_id()))]
pub async fn fetch_next(
&mut self,
) -> Vec<ListenEvent<T, ((Result<K, String>, Result<V, String>), T, D)>> {
let (parts, progress) = self.next(None).await;
let mut ret = Vec::with_capacity(parts.len() + 1);
for part in parts {
let fetched_part = self.fetch_batch_part(part).await;
let updates = fetched_part.collect::<Vec<_>>();
if !updates.is_empty() {
ret.push(ListenEvent::Updates(updates));
}
}
ret.push(ListenEvent::Progress(progress));
ret
}
/// Convert listener into futures::Stream
pub fn into_stream(
mut self,
) -> impl Stream<Item = ListenEvent<T, ((Result<K, String>, Result<V, String>), T, D)>> {
async_stream::stream!({
loop {
for msg in self.fetch_next().await {
yield msg;
}
}
})
}
/// Test helper to read from the listener until the given frontier is
/// reached. Because compaction can arbitrarily combine batches, we only
/// return the final progress info.
#[cfg(test)]
#[track_caller]
pub async fn read_until(
&mut self,
ts: &T,
) -> (
Vec<((Result<K, String>, Result<V, String>), T, D)>,
Antichain<T>,
) {
let mut updates = Vec::new();
let mut frontier = Antichain::from_elem(T::minimum());
while self.frontier.less_than(ts) {
for event in self.fetch_next().await {
match event {
ListenEvent::Updates(mut x) => updates.append(&mut x),
ListenEvent::Progress(x) => frontier = x,
}
}
}
// Unlike most tests, intentionally don't consolidate updates here
// because Listen replays them at the original fidelity.
(updates, frontier)
}
}
impl<K, V, T, D> Listen<K, V, T, D>
where
K: Debug + Codec,
V: Debug + Codec,
T: Timestamp + Lattice + Codec64,
D: Semigroup + Codec64 + Send + Sync,
{
/// Fetches the contents of `part` and returns its lease.
///
/// This is broken out into its own function to provide a trivial means for
/// [`Subscribe`], which contains a [`Listen`], to fetch batches.
async fn fetch_batch_part(&mut self, part: LeasedBatchPart<T>) -> FetchedPart<K, V, T, D> {
let fetched_part = fetch_leased_part(
&self.handle.cfg,
&part,
self.handle.blob.as_ref(),
Arc::clone(&self.handle.metrics),
&self.handle.metrics.read.listen,
&self.handle.machine.applier.shard_metrics,
&self.handle.reader_id,
self.handle.read_schemas.clone(),
&mut self.handle.schema_cache,
)
.await;
fetched_part
}
/// Politely expires this listen, releasing its lease.
///
/// There is a best-effort impl in Drop for [`ReadHandle`] to expire the
/// [`ReadHandle`] held by the listen that wasn't explicitly expired with
/// this method. When possible, explicit expiry is still preferred because
/// the Drop one is best effort and is dependant on a tokio [Handle] being
/// available in the TLC at the time of drop (which is a bit subtle). Also,
/// explicit expiry allows for control over when it happens.
pub async fn expire(self) {
self.handle.expire().await
}
}
/// A "capability" granting the ability to read the state of some shard at times
/// greater or equal to `self.since()`.
///
/// Production users should call [Self::expire] before dropping a ReadHandle so
/// that it can expire its leases. If/when rust gets AsyncDrop, this will be
/// done automatically.
///
/// All async methods on ReadHandle retry for as long as they are able, but the
/// returned [std::future::Future]s implement "cancel on drop" semantics. This
/// means that callers can add a timeout using [tokio::time::timeout] or
/// [tokio::time::timeout_at].
///
/// ```rust,no_run
/// # let mut read: mz_persist_client::read::ReadHandle<String, String, u64, i64> = unimplemented!();
/// # let timeout: std::time::Duration = unimplemented!();
/// # let new_since: timely::progress::Antichain<u64> = unimplemented!();
/// # async {
/// tokio::time::timeout(timeout, read.downgrade_since(&new_since)).await
/// # };
/// ```
#[derive(Debug)]
pub struct ReadHandle<K: Codec, V: Codec, T, D> {
pub(crate) cfg: PersistConfig,
pub(crate) metrics: Arc<Metrics>,
pub(crate) machine: Machine<K, V, T, D>,
pub(crate) gc: GarbageCollector<K, V, T, D>,
pub(crate) blob: Arc<dyn Blob>,
pub(crate) reader_id: LeasedReaderId,
pub(crate) read_schemas: Schemas<K, V>,
pub(crate) schema_cache: SchemaCache<K, V, T, D>,
since: Antichain<T>,
pub(crate) last_heartbeat: EpochMillis,
pub(crate) leased_seqnos: BTreeMap<SeqNo, Lease>,
pub(crate) unexpired_state: Option<UnexpiredReadHandleState>,
}
/// Length of time after a reader's last operation after which the reader may be
/// expired.
pub(crate) const READER_LEASE_DURATION: Config<Duration> = Config::new(
"persist_reader_lease_duration",
Duration::from_secs(60 * 15),
"The time after which we'll clean up stale read leases",
);
impl<K, V, T, D> ReadHandle<K, V, T, D>
where
K: Debug + Codec,
V: Debug + Codec,
T: Timestamp + Lattice + Codec64,
D: Semigroup + Codec64 + Send + Sync,
{
pub(crate) async fn new(
cfg: PersistConfig,
metrics: Arc<Metrics>,
machine: Machine<K, V, T, D>,
gc: GarbageCollector<K, V, T, D>,
blob: Arc<dyn Blob>,
reader_id: LeasedReaderId,
read_schemas: Schemas<K, V>,
since: Antichain<T>,
last_heartbeat: EpochMillis,
) -> Self {
let schema_cache = machine.applier.schema_cache();
let expire_fn = Self::expire_fn(machine.clone(), gc.clone(), reader_id.clone());
ReadHandle {
cfg,
metrics: Arc::clone(&metrics),
machine: machine.clone(),
gc: gc.clone(),
blob,
reader_id: reader_id.clone(),
read_schemas,
schema_cache,
since,
last_heartbeat,
leased_seqnos: BTreeMap::new(),
unexpired_state: Some(UnexpiredReadHandleState {
expire_fn,
_heartbeat_tasks: machine
.start_reader_heartbeat_tasks(reader_id, gc)
.await
.into_iter()
.map(JoinHandle::abort_on_drop)
.collect(),
}),
}
}
/// This handle's shard id.
pub fn shard_id(&self) -> ShardId {
self.machine.shard_id()
}
/// This handle's `since` frontier.
///
/// This will always be greater or equal to the shard-global `since`.
pub fn since(&self) -> &Antichain<T> {
&self.since
}
fn outstanding_seqno(&mut self) -> Option<SeqNo> {
while let Some(first) = self.leased_seqnos.first_entry() {
if first.get().count() <= 1 {
first.remove();
} else {
return Some(*first.key());
}
}
None
}
/// Forwards the since frontier of this handle, giving up the ability to
/// read at times not greater or equal to `new_since`.
///
/// This may trigger (asynchronous) compaction and consolidation in the
/// system. A `new_since` of the empty antichain "finishes" this shard,
/// promising that no more data will ever be read by this handle.
///
/// This also acts as a heartbeat for the reader lease (including if called
/// with `new_since` equal to something like `self.since()` or the minimum
/// timestamp, making the call a no-op).
#[instrument(level = "debug", fields(shard = %self.machine.shard_id()))]
pub async fn downgrade_since(&mut self, new_since: &Antichain<T>) {
// Guaranteed to be the smallest/oldest outstanding lease on a `SeqNo`.
let outstanding_seqno = self.outstanding_seqno();
let heartbeat_ts = (self.cfg.now)();
let (_seqno, current_reader_since, maintenance) = self
.machine
.downgrade_since(&self.reader_id, outstanding_seqno, new_since, heartbeat_ts)
.await;
// Debugging for database-issues#4590.
if let Some(outstanding_seqno) = outstanding_seqno {
let seqnos_held = _seqno.0.saturating_sub(outstanding_seqno.0);
// We get just over 1 seqno-per-second on average for a shard in
// prod, so this is about an hour.
const SEQNOS_HELD_THRESHOLD: u64 = 60 * 60;
if seqnos_held >= SEQNOS_HELD_THRESHOLD {
tracing::info!(
"{} reader {} holding an unexpected number of seqnos {} vs {}: {:?}. bt: {:?}",
self.machine.shard_id(),
self.reader_id,
outstanding_seqno,
_seqno,
self.leased_seqnos.keys().take(10).collect::<Vec<_>>(),
// The Debug impl of backtrace is less aesthetic, but will put the trace
// on a single line and play more nicely with our Honeycomb quota
Backtrace::capture(),
);
}
}
self.since = current_reader_since.0;
// A heartbeat is just any downgrade_since traffic, so update the
// internal rate limiter here to play nicely with `maybe_heartbeat`.
self.last_heartbeat = heartbeat_ts;
maintenance.start_performing(&self.machine, &self.gc);
}
/// Returns an ongoing subscription of updates to a shard.
///
/// The stream includes all data at times greater than `as_of`. Combined
/// with [Self::snapshot] it will produce exactly correct results: the
/// snapshot is the TVCs contents at `as_of` and all subsequent updates
/// occur at exactly their indicated time. The recipient should only
/// downgrade their read capability when they are certain they have all data
/// through the frontier they would downgrade to.
///
/// This takes ownership of the ReadHandle so the Listen can use it to
/// [Self::downgrade_since] as it progresses. If you need to keep this
/// handle, then [Self::clone] it before calling listen.
///
/// The `Since` error indicates that the requested `as_of` cannot be served
/// (the caller has out of date information) and includes the smallest
/// `as_of` that would have been accepted.
#[instrument(level = "debug", fields(shard = %self.machine.shard_id()))]
pub async fn listen(self, as_of: Antichain<T>) -> Result<Listen<K, V, T, D>, Since<T>> {
let () = self.machine.verify_listen(&as_of)?;
Ok(Listen::new(self, as_of).await)
}
/// Returns all of the contents of the shard TVC at `as_of` broken up into
/// [`LeasedBatchPart`]es. These parts can be "turned in" via
/// `crate::fetch::fetch_batch_part` to receive the data they contain.
///
/// This command returns the contents of this shard as of `as_of` once they
/// are known. This may "block" (in an async-friendly way) if `as_of` is
/// greater or equal to the current `upper` of the shard. The recipient
/// should only downgrade their read capability when they are certain they
/// have all data through the frontier they would downgrade to.
///
/// The `Since` error indicates that the requested `as_of` cannot be served
/// (the caller has out of date information) and includes the smallest
/// `as_of` that would have been accepted.
#[instrument(level = "trace", fields(shard = %self.machine.shard_id()))]
pub async fn snapshot(
&mut self,
as_of: Antichain<T>,
) -> Result<Vec<LeasedBatchPart<T>>, Since<T>> {
let batches = self.machine.snapshot(&as_of).await?;
if !PartialOrder::less_equal(self.since(), &as_of) {
return Err(Since(self.since().clone()));
}
let filter = FetchBatchFilter::Snapshot { as_of };
let mut leased_parts = Vec::new();
for batch in batches {
// Flatten the HollowBatch into one LeasedBatchPart per key. Each key
// corresponds to a "part" or s3 object. This allows persist_source
// to distribute work by parts (smallish, more even size) instead of
// batches (arbitrarily large).
leased_parts.extend(
self.lease_batch_parts(batch, filter.clone())
.collect::<Vec<_>>()
.await,
);
}
Ok(leased_parts)
}
/// Returns a snapshot of all of a shard's data using `as_of`, followed by
/// listening to any future updates.
///
/// For more details on this operation's semantics, see [Self::snapshot] and
/// [Self::listen].
#[instrument(level = "debug", fields(shard = %self.machine.shard_id()))]
pub async fn subscribe(
mut self,
as_of: Antichain<T>,
) -> Result<Subscribe<K, V, T, D>, Since<T>> {
let snapshot_parts = self.snapshot(as_of.clone()).await?;
let listen = self.listen(as_of.clone()).await?;
Ok(Subscribe::new(snapshot_parts, listen))
}
fn lease_batch_part(
&mut self,
desc: Description<T>,
part: BatchPart<T>,
filter: FetchBatchFilter<T>,
) -> LeasedBatchPart<T> {
LeasedBatchPart {
metrics: Arc::clone(&self.metrics),
shard_id: self.machine.shard_id(),
reader_id: self.reader_id.clone(),
filter,
desc,
part,
leased_seqno: self.machine.seqno(),
lease: Some(self.lease_seqno()),
filter_pushdown_audit: false,
}
}
fn lease_batch_parts(
&mut self,
batch: HollowBatch<T>,
filter: FetchBatchFilter<T>,
) -> impl Stream<Item = LeasedBatchPart<T>> + '_ {
stream! {
let blob = Arc::clone(&self.blob);
let metrics = Arc::clone(&self.metrics);
let desc = batch.desc.clone();
for await part in batch.part_stream(self.shard_id(), &*blob, &*metrics) {
yield self.lease_batch_part(desc.clone(), part.expect("leased part").into_owned(), filter.clone())
}
}
}
/// Tracks that the `ReadHandle`'s machine's current `SeqNo` is being
/// "leased out" to a `LeasedBatchPart`, and cannot be garbage
/// collected until its lease has been returned.
fn lease_seqno(&mut self) -> Lease {
let seqno = self.machine.seqno();
let lease = self.leased_seqnos.entry(seqno).or_default();
lease.clone()
}
/// Returns an independent [ReadHandle] with a new [LeasedReaderId] but the
/// same `since`.
#[instrument(level = "debug", fields(shard = %self.machine.shard_id()))]
pub async fn clone(&self, purpose: &str) -> Self {
let new_reader_id = LeasedReaderId::new();
let machine = self.machine.clone();
let gc = self.gc.clone();
let heartbeat_ts = (self.cfg.now)();
let (reader_state, maintenance) = machine
.register_leased_reader(
&new_reader_id,
purpose,
READER_LEASE_DURATION.get(&self.cfg),
heartbeat_ts,
false,
)
.await;
maintenance.start_performing(&machine, &gc);
// The point of clone is that you're guaranteed to have the same (or
// greater) since capability, verify that.
// TODO: better if it's the same since capability exactly.
assert!(PartialOrder::less_equal(&reader_state.since, &self.since));
let new_reader = ReadHandle::new(
self.cfg.clone(),
Arc::clone(&self.metrics),
machine,
gc,
Arc::clone(&self.blob),
new_reader_id,
self.read_schemas.clone(),
reader_state.since,
heartbeat_ts,
)
.await;
new_reader
}
/// A rate-limited version of [Self::downgrade_since].
///
/// This is an internally rate limited helper, designed to allow users to
/// call it as frequently as they like. Call this [Self::downgrade_since],
/// or Self::maybe_heartbeat_reader on some interval that is "frequent"
/// compared to PersistConfig::FAKE_READ_LEASE_DURATION.
///
/// This is communicating actual progress information, so is given
/// preferential treatment compared to Self::maybe_heartbeat_reader.
pub async fn maybe_downgrade_since(&mut self, new_since: &Antichain<T>) {
// NB: min_elapsed is intentionally smaller than the one in
// maybe_heartbeat_reader (this is the preferential treatment mentioned
// above).
let min_elapsed = READER_LEASE_DURATION.get(&self.cfg) / 4;
let elapsed_since_last_heartbeat =
Duration::from_millis((self.cfg.now)().saturating_sub(self.last_heartbeat));
if elapsed_since_last_heartbeat >= min_elapsed {
self.downgrade_since(new_since).await;
}
}
/// Heartbeats the read lease if necessary.
///
/// This is an internally rate limited helper, designed to allow users to
/// call it as frequently as they like. Call this [Self::downgrade_since],
/// or [Self::maybe_downgrade_since] on some interval that is "frequent"
/// compared to PersistConfig::FAKE_READ_LEASE_DURATION.
#[allow(dead_code)]
pub(crate) async fn maybe_heartbeat_reader(&mut self) {
let min_elapsed = READER_LEASE_DURATION.get(&self.cfg) / 2;
let heartbeat_ts = (self.cfg.now)();
let elapsed_since_last_heartbeat =
Duration::from_millis(heartbeat_ts.saturating_sub(self.last_heartbeat));
if elapsed_since_last_heartbeat >= min_elapsed {
if elapsed_since_last_heartbeat > READER_LEASE_DURATION.get(&self.machine.applier.cfg) {
warn!(
"reader ({}) of shard ({}) went {}s between heartbeats",
self.reader_id,
self.machine.shard_id(),
elapsed_since_last_heartbeat.as_secs_f64()
);
}
let (_, existed, maintenance) = self
.machine
.heartbeat_leased_reader(&self.reader_id, heartbeat_ts)
.await;
if !existed && !self.machine.applier.is_finalized() {
// It's probably surprising to the caller that the shard
// becoming a tombstone expired this reader. Possibly the right
// thing to do here is pass up a bool to the caller indicating
// whether the LeasedReaderId it's trying to heartbeat has been
// expired, but that happening on a tombstone vs not is very
// different. As a medium-term compromise, pretend we did the
// heartbeat here.
panic!(
"LeasedReaderId({}) was expired due to inactivity. Did the machine go to sleep?",
self.reader_id
)
}
self.last_heartbeat = heartbeat_ts;
maintenance.start_performing(&self.machine, &self.gc);
}
}
/// Politely expires this reader, releasing its lease.
///
/// There is a best-effort impl in Drop to expire a reader that wasn't
/// explictly expired with this method. When possible, explicit expiry is
/// still preferred because the Drop one is best effort and is dependant on
/// a tokio [Handle] being available in the TLC at the time of drop (which
/// is a bit subtle). Also, explicit expiry allows for control over when it
/// happens.
#[instrument(level = "debug", fields(shard = %self.machine.shard_id()))]
pub async fn expire(mut self) {
// We drop the unexpired state before expiring the reader to ensure the
// heartbeat tasks can never observe the expired state. This doesn't
// matter for correctness, but avoids confusing log output if the
// heartbeat task were to discover that its lease has been expired.
let Some(unexpired_state) = self.unexpired_state.take() else {
return;
};
unexpired_state.expire_fn.0().await;
}
fn expire_fn(
machine: Machine<K, V, T, D>,
gc: GarbageCollector<K, V, T, D>,
reader_id: LeasedReaderId,
) -> ExpireFn {
ExpireFn(Box::new(move || {
Box::pin(async move {
let (_, maintenance) = machine.expire_leased_reader(&reader_id).await;
maintenance.start_performing(&machine, &gc);
})
}))
}
/// Test helper for a [Self::listen] call that is expected to succeed.
#[cfg(test)]
#[track_caller]
pub async fn expect_listen(self, as_of: T) -> Listen<K, V, T, D> {
self.listen(Antichain::from_elem(as_of))
.await
.expect("cannot serve requested as_of")
}
}
/// State for a read handle that has not been explicitly expired.
#[derive(Debug)]
pub(crate) struct UnexpiredReadHandleState {
expire_fn: ExpireFn,
pub(crate) _heartbeat_tasks: Vec<AbortOnDropHandle<()>>,
}
/// An incremental cursor through a particular shard, returned from [ReadHandle::snapshot_cursor].
///
/// To read an entire dataset, the
/// client should call `next` until it returns `None`, which signals all data has been returned...
/// but it's also free to abandon the instance at any time if it eg. only needs a few entries.
#[derive(Debug)]
pub struct Cursor<K: Codec, V: Codec, T: Timestamp + Codec64, D: Codec64> {
consolidator: CursorConsolidator<K, V, T, D>,
_lease: Lease,
read_schemas: Schemas<K, V>,
}
#[derive(Debug)]
enum CursorConsolidator<K: Codec, V: Codec, T: Timestamp + Codec64, D: Codec64> {
Codec {
consolidator: Consolidator<T, D, CodecSort<T, D>>,
},
Structured {
consolidator: Consolidator<T, D, StructuredSort<K, V, T, D>>,
max_len: usize,
max_bytes: usize,
},
}
impl<K, V, T, D> Cursor<K, V, T, D>
where
K: Debug + Codec + Ord,
V: Debug + Codec + Ord,
T: Timestamp + Lattice + Codec64,
D: Semigroup + Ord + Codec64 + Send + Sync,
{
/// Grab the next batch of consolidated data.
pub async fn next(
&mut self,
) -> Option<impl Iterator<Item = ((Result<K, String>, Result<V, String>), T, D)> + '_> {
match &mut self.consolidator {
CursorConsolidator::Structured {
consolidator,
max_len,
max_bytes,
} => {
let mut iter = consolidator
.next_chunk(*max_len, *max_bytes)
.await
.expect("fetching a leased part")?;
let structured = iter.get_or_make_structured::<K, V>(
self.read_schemas.key.as_ref(),
self.read_schemas.val.as_ref(),
);
let key_decoder = self
.read_schemas
.key
.decoder_any(structured.key.as_ref())
.expect("ok");
let val_decoder = self
.read_schemas
.val
.decoder_any(structured.val.as_ref())
.expect("ok");
let iter = (0..iter.len()).map(move |i| {
let mut k = K::default();
let mut v = V::default();
key_decoder.decode(i, &mut k);
val_decoder.decode(i, &mut v);
let t = T::decode(iter.records().timestamps().value(i).to_le_bytes());
let d = D::decode(iter.records().diffs().value(i).to_le_bytes());
((Ok(k), Ok(v)), t, d)
});
Some(Either::Left(iter))
}
CursorConsolidator::Codec { consolidator } => {
let iter = consolidator
.next()
.await
.expect("fetching a leased part")?
.map(|((k, v), t, d)| {
let key = K::decode(k, &self.read_schemas.key);
let val = V::decode(v, &self.read_schemas.val);
((key, val), t, d)
});
Some(Either::Right(iter))
}
}
}
}
impl<K, V, T, D> ReadHandle<K, V, T, D>
where
K: Debug + Codec + Ord,
V: Debug + Codec + Ord,
T: Timestamp + Lattice + Codec64,
D: Semigroup + Ord + Codec64 + Send + Sync,
{
/// Generates a [Self::snapshot], and fetches all of the batches it
/// contains.
///
/// The output is consolidated. Furthermore, to keep memory usage down when
/// reading a snapshot that consolidates well, this consolidates as it goes.
///
/// Potential future improvements (if necessary):
/// - Accept something like a `F: Fn(K,V) -> (K,V)` argument, which looks
/// like an MFP you might be pushing down. Reason being that if you are
/// projecting or transforming in a way that allows further consolidation,
/// amazing.
/// - Reuse any code we write to streaming-merge consolidate in
/// persist_source here.
pub async fn snapshot_and_fetch(
&mut self,
as_of: Antichain<T>,
) -> Result<Vec<((Result<K, String>, Result<V, String>), T, D)>, Since<T>> {
let mut cursor = self.snapshot_cursor(as_of, |_| true).await?;
let mut contents = Vec::new();
while let Some(iter) = cursor.next().await {
contents.extend(iter);
}
// We don't currently guarantee that encoding is one-to-one, so we still need to
// consolidate the decoded outputs. However, let's report if this isn't a noop.
let old_len = contents.len();
consolidate_updates(&mut contents);
if old_len != contents.len() {
// TODO(bkirwi): do we need more / finer-grained metrics for this?
self.machine
.applier
.shard_metrics
.unconsolidated_snapshot
.inc();
}
Ok(contents)
}
/// Generates a [Self::snapshot], and fetches all of the batches it
/// contains.
///
/// To keep memory usage down when reading a snapshot that consolidates well, this consolidates
/// as it goes. However, note that only the serialized data is consolidated: the deserialized
/// data will only be consolidated if your K/V codecs are one-to-one.
pub async fn snapshot_cursor(
&mut self,
as_of: Antichain<T>,
should_fetch_part: impl for<'a> Fn(Option<&'a LazyPartStats>) -> bool,
) -> Result<Cursor<K, V, T, D>, Since<T>> {
let batches = self.machine.snapshot(&as_of).await?;
let context = format!("{}[as_of={:?}]", self.shard_id(), as_of.elements());
let filter = FetchBatchFilter::Snapshot {
as_of: as_of.clone(),
};
let lease = self.lease_seqno();
let structured_order = STRUCTURED_ORDER.get(&self.cfg) && {
self.shard_id().to_string() < STRUCTURED_ORDER_UNTIL_SHARD.get(&self.cfg)
};
let consolidator = if structured_order {
let mut consolidator = Consolidator::new(
context,
self.shard_id(),
StructuredSort::new(self.read_schemas.clone()),
Arc::clone(&self.blob),
Arc::clone(&self.metrics),
Arc::clone(&self.machine.applier.shard_metrics),
self.metrics.read.snapshot.clone(),
filter,
self.cfg.dynamic.compaction_memory_bound_bytes(),
);
for batch in batches {
for (meta, run) in batch.runs() {
consolidator.enqueue_run(
&batch.desc,
meta,
run.into_iter()
.filter(|p| should_fetch_part(p.stats()))
.cloned(),
);
}
}
CursorConsolidator::Structured {
consolidator,
// This default may end up consolidating more records than previously
// for cases like fast-path peeks, where only the first few entries are used.
// If this is a noticeable performance impact, thread the max-len in from the caller.
max_len: self.cfg.compaction_yield_after_n_updates,
max_bytes: BLOB_TARGET_SIZE.get(&self.cfg).max(1),
}
} else {
let mut consolidator = Consolidator::new(
context,
self.shard_id(),
CodecSort::default(),
Arc::clone(&self.blob),
Arc::clone(&self.metrics),
Arc::clone(&self.machine.applier.shard_metrics),
self.metrics.read.snapshot.clone(),
filter,
self.cfg.dynamic.compaction_memory_bound_bytes(),
);
for batch in batches {
for (meta, run) in batch.runs() {
consolidator.enqueue_run(
&batch.desc,
meta,
run.into_iter()
.filter(|p| should_fetch_part(p.stats()))
.cloned(),
);
}
}
CursorConsolidator::Codec { consolidator }
};
Ok(Cursor {
consolidator,
_lease: lease,
read_schemas: self.read_schemas.clone(),
})
}
/// Returns aggregate statistics about the contents of the shard TVC at the
/// given frontier.
///
/// This command returns the contents of this shard as of `as_of` once they
/// are known. This may "block" (in an async-friendly way) if `as_of` is
/// greater or equal to the current `upper` of the shard. If `None` is given
/// for `as_of`, then the latest stats known by this process are used.
///
/// The `Since` error indicates that the requested `as_of` cannot be served
/// (the caller has out of date information) and includes the smallest
/// `as_of` that would have been accepted.
pub fn snapshot_stats(
&self,
as_of: Option<Antichain<T>>,
) -> impl Future<Output = Result<SnapshotStats, Since<T>>> + Send + 'static {
let machine = self.machine.clone();
async move {
let batches = match as_of {
Some(as_of) => machine.snapshot(&as_of).await?,
None => machine.applier.all_batches(),
};
let num_updates = batches.iter().map(|b| b.len).sum();
Ok(SnapshotStats {
shard_id: machine.shard_id(),
num_updates,
})
}
}
/// Returns aggregate statistics about the contents of the shard TVC at the
/// given frontier.
///
/// This command returns the contents of this shard as of `as_of` once they
/// are known. This may "block" (in an async-friendly way) if `as_of` is
/// greater or equal to the current `upper` of the shard.
///
/// The `Since` error indicates that the requested `as_of` cannot be served
/// (the caller has out of date information) and includes the smallest
/// `as_of` that would have been accepted.
pub async fn snapshot_parts_stats(
&self,
as_of: Antichain<T>,
) -> Result<SnapshotPartsStats, Since<T>> {
let batches = self.machine.snapshot(&as_of).await?;
let parts = stream::iter(&batches)
.flat_map(|b| b.part_stream(self.shard_id(), &*self.blob, &*self.metrics))
.map(|p| {
let p = p.expect("live batch");
SnapshotPartStats {
encoded_size_bytes: p.encoded_size_bytes(),
stats: p.stats().cloned(),
}
})
.collect()
.await;
Ok(SnapshotPartsStats {
metrics: Arc::clone(&self.machine.applier.metrics),
shard_id: self.machine.shard_id(),
parts,
})
}
}
impl<K, V, T, D> ReadHandle<K, V, T, D>
where
K: Debug + Codec + Ord,
V: Debug + Codec + Ord,
T: Timestamp + Lattice + Codec64,
D: Semigroup + Codec64 + Send + Sync,
{
/// Generates a [Self::snapshot], and streams out all of the updates
/// it contains in bounded memory.
///
/// The output is not consolidated.
pub async fn snapshot_and_stream(
&mut self,
as_of: Antichain<T>,
) -> Result<impl Stream<Item = ((Result<K, String>, Result<V, String>), T, D)>, Since<T>> {
let snap = self.snapshot(as_of).await?;
let blob = Arc::clone(&self.blob);
let metrics = Arc::clone(&self.metrics);
let snapshot_metrics = self.metrics.read.snapshot.clone();
let shard_metrics = Arc::clone(&self.machine.applier.shard_metrics);
let reader_id = self.reader_id.clone();
let schemas = self.read_schemas.clone();
let mut schema_cache = self.schema_cache.clone();
let persist_cfg = self.cfg.clone();
let stream = async_stream::stream! {
for part in snap {
let mut fetched_part = fetch_leased_part(
&persist_cfg,
&part,
blob.as_ref(),
Arc::clone(&metrics),
&snapshot_metrics,
&shard_metrics,
&reader_id,
schemas.clone(),
&mut schema_cache,
)
.await;
while let Some(next) = fetched_part.next() {
yield next;
}
}
};
Ok(stream)
}
}
impl<K, V, T, D> ReadHandle<K, V, T, D>
where
K: Debug + Codec + Ord,
V: Debug + Codec + Ord,
T: Timestamp + Lattice + Codec64 + Ord,
D: Semigroup + Ord + Codec64 + Send + Sync,
{
/// Test helper to generate a [Self::snapshot] call that is expected to
/// succeed, process its batches, and then return its data sorted.
#[cfg(test)]
#[track_caller]
pub async fn expect_snapshot_and_fetch(
&mut self,
as_of: T,
) -> Vec<((Result<K, String>, Result<V, String>), T, D)> {
let mut ret = self
.snapshot_and_fetch(Antichain::from_elem(as_of))
.await
.expect("cannot serve requested as_of");
ret.sort();
ret
}
}
impl<K: Codec, V: Codec, T, D> Drop for ReadHandle<K, V, T, D> {
fn drop(&mut self) {
// We drop the unexpired state before expiring the reader to ensure the
// heartbeat tasks can never observe the expired state. This doesn't
// matter for correctness, but avoids confusing log output if the
// heartbeat task were to discover that its lease has been expired.
let Some(unexpired_state) = self.unexpired_state.take() else {
return;
};
let handle = match Handle::try_current() {
Ok(x) => x,
Err(_) => {
warn!("ReadHandle {} dropped without being explicitly expired, falling back to lease timeout", self.reader_id);
return;
}
};
// Spawn a best-effort task to expire this read handle. It's fine if
// this doesn't run to completion, we'd just have to wait out the lease
// before the shard-global since is unblocked.
//
// Intentionally create the span outside the task to set the parent.
let expire_span = debug_span!("drop::expire");
handle.spawn_named(
|| format!("ReadHandle::expire ({})", self.reader_id),
unexpired_state.expire_fn.0().instrument(expire_span),
);
}
}
#[cfg(test)]
mod tests {
use std::pin;
use std::str::FromStr;
use mz_dyncfg::ConfigUpdates;
use mz_ore::cast::CastFrom;
use mz_ore::metrics::MetricsRegistry;
use mz_persist::mem::{MemBlob, MemBlobConfig, MemConsensus};
use mz_persist::unreliable::{UnreliableConsensus, UnreliableHandle};
use serde::{Deserialize, Serialize};
use serde_json::json;
use tokio_stream::StreamExt;
use crate::async_runtime::IsolatedRuntime;
use crate::batch::BLOB_TARGET_SIZE;
use crate::cache::StateCache;
use crate::internal::metrics::Metrics;
use crate::rpc::NoopPubSubSender;
use crate::tests::{all_ok, new_test_client};
use crate::{Diagnostics, PersistClient, PersistConfig, ShardId};
use super::*;
// Verifies `Subscribe` can be dropped while holding snapshot batches.
#[mz_persist_proc::test(tokio::test)]
#[cfg_attr(miri, ignore)] // unsupported operation: returning ready events from epoll_wait is not yet implemented
async fn drop_unused_subscribe(dyncfgs: ConfigUpdates) {
let data = [
(("0".to_owned(), "zero".to_owned()), 0, 1),
(("1".to_owned(), "one".to_owned()), 1, 1),
(("2".to_owned(), "two".to_owned()), 2, 1),
];
let (mut write, read) = new_test_client(&dyncfgs)
.await
.expect_open::<String, String, u64, i64>(crate::ShardId::new())
.await;
write.expect_compare_and_append(&data[0..1], 0, 1).await;
write.expect_compare_and_append(&data[1..2], 1, 2).await;
write.expect_compare_and_append(&data[2..3], 2, 3).await;
let subscribe = read
.subscribe(timely::progress::Antichain::from_elem(2))
.await
.unwrap();
assert!(
!subscribe.snapshot.as_ref().unwrap().is_empty(),
"snapshot must have batches for test to be meaningful"
);
drop(subscribe);
}
// Verifies that we streaming-consolidate away identical key-values in the same batch.
#[mz_persist_proc::test(tokio::test)]
#[cfg_attr(miri, ignore)] // unsupported operation: returning ready events from epoll_wait is not yet implemented
async fn streaming_consolidate(dyncfgs: ConfigUpdates) {
let data = &[
// Identical records should sum together...
(("k".to_owned(), "v".to_owned()), 0, 1),
(("k".to_owned(), "v".to_owned()), 1, 1),
(("k".to_owned(), "v".to_owned()), 2, 1),
// ...and when they cancel out entirely they should be omitted.
(("k2".to_owned(), "v".to_owned()), 0, 1),
(("k2".to_owned(), "v".to_owned()), 1, -1),
];
let (mut write, read) = {
let client = new_test_client(&dyncfgs).await;
client.cfg.set_config(&BLOB_TARGET_SIZE, 1000); // So our batch stays together!
client
.expect_open::<String, String, u64, i64>(crate::ShardId::new())
.await
};
write.expect_compare_and_append(data, 0, 5).await;
let mut snapshot = read
.subscribe(timely::progress::Antichain::from_elem(4))
.await
.unwrap();
let mut updates = vec![];
'outer: loop {
for event in snapshot.fetch_next().await {
match event {
ListenEvent::Progress(t) => {
if !t.less_than(&4) {
break 'outer;
}
}
ListenEvent::Updates(data) => {
updates.extend(data);
}
}
}
}
assert_eq!(
updates,
&[((Ok("k".to_owned()), Ok("v".to_owned())), 4u64, 3i64)],
)
}
#[mz_persist_proc::test(tokio::test)]
#[cfg_attr(miri, ignore)] // unsupported operation: returning ready events from epoll_wait is not yet implemented
async fn snapshot_and_stream(dyncfgs: ConfigUpdates) {
let data = &mut [
(("k1".to_owned(), "v1".to_owned()), 0, 1),
(("k2".to_owned(), "v2".to_owned()), 1, 1),
(("k3".to_owned(), "v3".to_owned()), 2, 1),
(("k4".to_owned(), "v4".to_owned()), 2, 1),
(("k5".to_owned(), "v5".to_owned()), 3, 1),
];
let (mut write, mut read) = {
let client = new_test_client(&dyncfgs).await;
client.cfg.set_config(&BLOB_TARGET_SIZE, 0); // split batches across multiple parts
client
.expect_open::<String, String, u64, i64>(crate::ShardId::new())
.await
};
write.expect_compare_and_append(&data[0..2], 0, 2).await;
write.expect_compare_and_append(&data[2..4], 2, 3).await;
write.expect_compare_and_append(&data[4..], 3, 4).await;
let as_of = Antichain::from_elem(3);
let mut snapshot = pin::pin!(read.snapshot_and_stream(as_of.clone()).await.unwrap());
let mut snapshot_rows = vec![];
while let Some(((k, v), t, d)) = snapshot.next().await {
snapshot_rows.push(((k.expect("valid key"), v.expect("valid key")), t, d));
}
for ((_k, _v), t, _d) in data.as_mut_slice() {
t.advance_by(as_of.borrow());
}
assert_eq!(data.as_slice(), snapshot_rows.as_slice());
}
// Verifies the semantics of `SeqNo` leases + checks dropping `LeasedBatchPart` semantics.
#[mz_persist_proc::test(tokio::test)]
#[cfg_attr(miri, ignore)] // https://github.com/MaterializeInc/database-issues/issues/5964
async fn seqno_leases(dyncfgs: ConfigUpdates) {
let mut data = vec![];
for i in 0..20 {
data.push(((i.to_string(), i.to_string()), i, 1))
}
let shard_id = ShardId::new();
let client = new_test_client(&dyncfgs).await;
let (mut write, read) = client
.expect_open::<String, String, u64, i64>(shard_id)
.await;
// Seed with some values
let mut offset = 0;
let mut width = 2;
for i in offset..offset + width {
write
.expect_compare_and_append(
&data[i..i + 1],
u64::cast_from(i),
u64::cast_from(i) + 1,
)
.await;
}
offset += width;
// Create machinery for subscribe + fetch
let mut fetcher = client
.create_batch_fetcher::<String, String, u64, i64>(
shard_id,
Default::default(),
Default::default(),
false,
Diagnostics::for_tests(),
)
.await
.unwrap();
let mut subscribe = read
.subscribe(timely::progress::Antichain::from_elem(1))
.await
.expect("cannot serve requested as_of");
// Determine sequence number at outset.
let original_seqno_since = subscribe.listen.handle.machine.applier.seqno_since();
let mut parts = vec![];
width = 4;
// Collect parts while continuing to write values
for i in offset..offset + width {
for event in subscribe.next(None).await {
if let ListenEvent::Updates(mut new_parts) = event {
parts.append(&mut new_parts);
// Here and elsewhere we "cheat" and immediately downgrade the since
// to demonstrate the effects of SeqNo leases immediately.
subscribe
.listen
.handle
.downgrade_since(&subscribe.listen.since)
.await;
}
}
write
.expect_compare_and_append(
&data[i..i + 1],
u64::cast_from(i),
u64::cast_from(i) + 1,
)
.await;
// SeqNo is not downgraded
assert_eq!(
subscribe.listen.handle.machine.applier.seqno_since(),
original_seqno_since
);
}
offset += width;
let mut seqno_since = subscribe.listen.handle.machine.applier.seqno_since();
// We're starting out with the original, non-downgraded SeqNo
assert_eq!(seqno_since, original_seqno_since);
// We have to handle the parts we generate during the next loop to
// ensure they don't panic.
let mut subsequent_parts = vec![];
// Ensure monotonicity of seqnos we're processing, otherwise the
// invariant we're testing (returning the last part of a seqno will
// downgrade its since) will not hold.
let mut this_seqno = SeqNo::minimum();
// Repeat the same process as above, more or less, while fetching + returning parts
for (mut i, part) in parts.into_iter().enumerate() {
let part_seqno = part.leased_seqno;
let last_seqno = this_seqno;
this_seqno = part_seqno;
assert!(this_seqno >= last_seqno);
let _ = fetcher.fetch_leased_part(&part).await;
drop(part);
// Simulates an exchange
for event in subscribe.next(None).await {
if let ListenEvent::Updates(parts) = event {
for part in parts {
if let (_, Some(lease)) = part.into_exchangeable_part() {
subsequent_parts.push(lease);
}
}
}
}
subscribe
.listen
.handle
.downgrade_since(&subscribe.listen.since)
.await;
// Write more new values
i += offset;
write
.expect_compare_and_append(
&data[i..i + 1],
u64::cast_from(i),
u64::cast_from(i) + 1,
)
.await;
// We should expect the SeqNo to be downgraded if this part's SeqNo
// is no longer leased to any other parts, either.
let expect_downgrade = subscribe.listen.handle.outstanding_seqno() > Some(part_seqno);
let new_seqno_since = subscribe.listen.handle.machine.applier.seqno_since();
if expect_downgrade {
assert!(new_seqno_since > seqno_since);
} else {
assert_eq!(new_seqno_since, seqno_since);
}
seqno_since = new_seqno_since;
}
// SeqNo since was downgraded
assert!(seqno_since > original_seqno_since);
// Return any outstanding parts, to prevent a panic!
drop(subsequent_parts);
drop(subscribe);
}
#[mz_ore::test]
fn reader_id_human_readable_serde() {
#[derive(Debug, Serialize, Deserialize)]
struct Container {
reader_id: LeasedReaderId,
}
// roundtrip through json
let id =
LeasedReaderId::from_str("r00000000-1234-5678-0000-000000000000").expect("valid id");
assert_eq!(
id,
serde_json::from_value(serde_json::to_value(id.clone()).expect("serializable"))
.expect("deserializable")
);
// deserialize a serialized string directly
assert_eq!(
id,
serde_json::from_str("\"r00000000-1234-5678-0000-000000000000\"")
.expect("deserializable")
);
// roundtrip id through a container type
let json = json!({ "reader_id": id });
assert_eq!(
"{\"reader_id\":\"r00000000-1234-5678-0000-000000000000\"}",
&json.to_string()
);
let container: Container = serde_json::from_value(json).expect("deserializable");
assert_eq!(container.reader_id, id);
}
// Verifies performance optimizations where a Listener doesn't fetch the
// latest Consensus state if the one it currently has can serve the next
// request.
#[mz_ore::test(tokio::test)]
#[cfg_attr(miri, ignore)] // too slow
async fn skip_consensus_fetch_optimization() {
let data = vec![
(("0".to_owned(), "zero".to_owned()), 0, 1),
(("1".to_owned(), "one".to_owned()), 1, 1),
(("2".to_owned(), "two".to_owned()), 2, 1),
];
let cfg = PersistConfig::new_for_tests();
let blob = Arc::new(MemBlob::open(MemBlobConfig::default()));
let consensus = Arc::new(MemConsensus::default());
let unreliable = UnreliableHandle::default();
unreliable.totally_available();
let consensus = Arc::new(UnreliableConsensus::new(consensus, unreliable.clone()));
let metrics = Arc::new(Metrics::new(&cfg, &MetricsRegistry::new()));
let pubsub_sender = Arc::new(NoopPubSubSender);
let (mut write, mut read) = PersistClient::new(
cfg,
blob,
consensus,
metrics,
Arc::new(IsolatedRuntime::default()),
Arc::new(StateCache::new_no_metrics()),
pubsub_sender,
)
.expect("client construction failed")
.expect_open::<String, String, u64, i64>(ShardId::new())
.await;
write.expect_compare_and_append(&data[0..1], 0, 1).await;
write.expect_compare_and_append(&data[1..2], 1, 2).await;
write.expect_compare_and_append(&data[2..3], 2, 3).await;
let snapshot = read.expect_snapshot_and_fetch(2).await;
let mut listen = read.expect_listen(0).await;
// Manually advance the listener's machine so that it has the latest
// state by fetching the first events from next. This is awkward but
// only necessary because we're about to do some weird things with
// unreliable.
let listen_actual = listen.fetch_next().await;
let expected_events = vec![ListenEvent::Progress(Antichain::from_elem(1))];
assert_eq!(listen_actual, expected_events);
// At this point, the snapshot and listen's state should have all the
// writes. Test this by making consensus completely unavailable.
unreliable.totally_unavailable();
assert_eq!(snapshot, all_ok(&data, 2));
assert_eq!(
listen.read_until(&3).await,
(all_ok(&data[1..], 1), Antichain::from_elem(3))
);
}
}