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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.
//! A source that reads from an a persist shard.
use differential_dataflow::consolidation::ConsolidatingContainerBuilder;
use mz_dyncfg::ConfigSet;
use mz_persist_client::project::{error_free, ProjectionPushdown};
use std::convert::Infallible;
use std::fmt::Debug;
use std::future::Future;
use std::hash::Hash;
use std::pin::Pin;
use std::sync::Arc;
use std::time::Instant;
use differential_dataflow::lattice::Lattice;
use futures::{future::Either, StreamExt};
use mz_expr::{ColumnSpecs, Interpreter, MfpPlan, ResultSpec, UnmaterializableFunc};
use mz_ore::cast::CastFrom;
use mz_ore::collections::CollectionExt;
use mz_ore::vec::VecExt;
use mz_persist_client::cache::PersistClientCache;
use mz_persist_client::cfg::{PersistConfig, RetryParameters};
use mz_persist_client::fetch::{FetchedBlob, FetchedPart};
use mz_persist_client::fetch::{SerdeLeasedBatchPart, ShardSourcePart};
use mz_persist_client::operators::shard_source::{shard_source, SnapshotMode};
use mz_persist_types::codec_impls::UnitSchema;
use mz_persist_types::{Codec, Codec64};
use mz_repr::{Datum, DatumVec, Diff, GlobalId, RelationType, Row, RowArena, Timestamp};
use mz_storage_types::controller::{CollectionMetadata, TxnsCodecRow};
use mz_storage_types::errors::DataflowError;
use mz_storage_types::sources::SourceData;
use mz_storage_types::stats::RelationPartStats;
use mz_timely_util::builder_async::{
Event, OperatorBuilder as AsyncOperatorBuilder, PressOnDropButton,
};
use mz_timely_util::probe::ProbeNotify;
use mz_txn_wal::operator::{txns_progress, TxnsContext};
use serde::{Deserialize, Serialize};
use timely::communication::Push;
use timely::dataflow::channels::pact::Pipeline;
use timely::dataflow::channels::Bundle;
use timely::dataflow::operators::generic::builder_rc::OperatorBuilder;
use timely::dataflow::operators::generic::OutputHandleCore;
use timely::dataflow::operators::{Capability, Leave, OkErr};
use timely::dataflow::operators::{CapabilitySet, ConnectLoop, Feedback};
use timely::dataflow::scopes::Child;
use timely::dataflow::ScopeParent;
use timely::dataflow::{Scope, Stream};
use timely::order::TotalOrder;
use timely::progress::timestamp::PathSummary;
use timely::progress::Antichain;
use timely::progress::Timestamp as TimelyTimestamp;
use timely::scheduling::Activator;
use timely::PartialOrder;
use tokio::sync::mpsc::UnboundedSender;
use tracing::trace;
use crate::metrics::BackpressureMetrics;
/// This opaque token represents progress within a timestamp, allowing finer-grained frontier
/// progress than would otherwise be possible.
///
/// This is "opaque" since we'd like to reserve the right to change the definition in the future
/// without downstreams being able to rely on the precise representation. (At the moment, this
/// is a simple batch counter, though we may change it to eg. reflect progress through the keyspace
/// in the future.)
#[derive(
Copy, Clone, PartialEq, Default, Eq, PartialOrd, Ord, Debug, Serialize, Deserialize, Hash,
)]
pub struct Subtime(u64);
impl PartialOrder for Subtime {
fn less_equal(&self, other: &Self) -> bool {
self.0.less_equal(&other.0)
}
}
impl TotalOrder for Subtime {}
impl PathSummary<Subtime> for Subtime {
fn results_in(&self, src: &Subtime) -> Option<Subtime> {
self.0.results_in(&src.0).map(Subtime)
}
fn followed_by(&self, other: &Self) -> Option<Self> {
self.0.followed_by(&other.0).map(Subtime)
}
}
impl TimelyTimestamp for Subtime {
type Summary = Subtime;
fn minimum() -> Self {
Subtime(0)
}
}
impl Subtime {
/// The smallest non-zero summary for the opaque timestamp type.
pub const fn least_summary() -> Self {
Subtime(1)
}
}
/// Creates a new source that reads from a persist shard, distributing the work
/// of reading data to all timely workers.
///
/// All times emitted will have been [advanced by] the given `as_of` frontier.
/// All updates at times greater or equal to `until` will be suppressed.
/// The `map_filter_project` argument, if supplied, may be partially applied,
/// and any un-applied part of the argument will be left behind in the argument.
///
/// Users of this function have the ability to apply flow control to the output
/// to limit the in-flight data (measured in bytes) it can emit. The flow control
/// input is a timely stream that communicates the frontier at which the data
/// emitted from by this source have been dropped.
///
/// **Note:** Because this function is reading batches from `persist`, it is working
/// at batch granularity. In practice, the source will be overshooting the target
/// flow control upper by an amount that is related to the size of batches.
///
/// If no flow control is desired an empty stream whose frontier immediately advances
/// to the empty antichain can be used. An easy easy of creating such stream is by
/// using [`timely::dataflow::operators::generic::operator::empty`].
///
/// [advanced by]: differential_dataflow::lattice::Lattice::advance_by
pub fn persist_source<G>(
scope: &mut G,
source_id: GlobalId,
persist_clients: Arc<PersistClientCache>,
txns_ctx: &TxnsContext,
// In case we need to use a dyncfg to decide which operators to render in a
// dataflow.
worker_dyncfgs: &ConfigSet,
metadata: CollectionMetadata,
as_of: Option<Antichain<Timestamp>>,
snapshot_mode: SnapshotMode,
until: Antichain<Timestamp>,
map_filter_project: Option<&mut MfpPlan>,
max_inflight_bytes: Option<usize>,
start_signal: impl Future<Output = ()> + 'static,
error_handler: impl FnOnce(String) -> Pin<Box<dyn Future<Output = ()>>> + 'static,
) -> (
Stream<G, (Row, Timestamp, Diff)>,
Stream<G, (DataflowError, Timestamp, Diff)>,
Vec<PressOnDropButton>,
)
where
G: Scope<Timestamp = mz_repr::Timestamp>,
{
let shard_metrics = persist_clients.shard_metrics(&metadata.data_shard, &source_id.to_string());
let mut tokens = vec![];
let stream = scope.scoped(&format!("granular_backpressure({})", source_id), |scope| {
let (flow_control, flow_control_probe) = match max_inflight_bytes {
Some(max_inflight_bytes) => {
let backpressure_metrics = BackpressureMetrics {
emitted_bytes: Arc::clone(&shard_metrics.backpressure_emitted_bytes),
last_backpressured_bytes: Arc::clone(
&shard_metrics.backpressure_last_backpressured_bytes,
),
retired_bytes: Arc::clone(&shard_metrics.backpressure_retired_bytes),
};
let probe = mz_timely_util::probe::Handle::default();
let progress_stream = mz_timely_util::probe::source(
scope.clone(),
format!("decode_backpressure_probe({source_id})"),
probe.clone(),
);
let flow_control = FlowControl {
progress_stream,
max_inflight_bytes,
summary: (Default::default(), Subtime::least_summary()),
metrics: Some(backpressure_metrics),
};
(Some(flow_control), Some(probe))
}
None => (None, None),
};
// Our default listen sleeps are tuned for the case of a shard that is
// written once a second, but txn-wal allows these to be lazy.
// Override the tuning to reduce crdb load. The pubsub fallback
// responsibility is then replaced by manual "one state" wakeups in the
// txns_progress operator.
let cfg = Arc::clone(&persist_clients.cfg().configs);
let subscribe_sleep = match metadata.txns_shard {
Some(_) => Some(move || mz_txn_wal::operator::txns_data_shard_retry_params(&cfg)),
None => None,
};
let (stream, source_tokens) = persist_source_core(
scope,
source_id,
Arc::clone(&persist_clients),
metadata.clone(),
as_of.clone(),
snapshot_mode,
until.clone(),
map_filter_project,
flow_control,
subscribe_sleep,
start_signal,
error_handler,
);
tokens.extend(source_tokens);
let stream = match flow_control_probe {
Some(probe) => stream.probe_notify_with(vec![probe]),
None => stream,
};
stream.leave()
});
// If a txns_shard was provided, then this shard is in the txn-wal
// system. This means the "logical" upper may be ahead of the "physical"
// upper. Render a dataflow operator that passes through the input and
// translates the progress frontiers as necessary.
let (stream, txns_tokens) = match metadata.txns_shard {
Some(txns_shard) => txns_progress::<SourceData, (), Timestamp, i64, _, TxnsCodecRow, _, _>(
stream,
&source_id.to_string(),
txns_ctx,
worker_dyncfgs,
move || {
let (c, l) = (
Arc::clone(&persist_clients),
metadata.persist_location.clone(),
);
async move { c.open(l).await.expect("location is valid") }
},
txns_shard,
metadata.data_shard,
as_of
.expect("as_of is provided for table sources")
.into_option()
.expect("shard is not closed"),
until,
Arc::new(metadata.relation_desc),
Arc::new(UnitSchema),
),
None => (stream, vec![]),
};
tokens.extend(txns_tokens);
let (ok_stream, err_stream) = stream.ok_err(|(d, t, r)| match d {
Ok(row) => Ok((row, t.0, r)),
Err(err) => Err((err, t.0, r)),
});
(ok_stream, err_stream, tokens)
}
type RefinedScope<'g, G> = Child<'g, G, (<G as ScopeParent>::Timestamp, Subtime)>;
/// Creates a new source that reads from a persist shard, distributing the work
/// of reading data to all timely workers.
///
/// All times emitted will have been [advanced by] the given `as_of` frontier.
///
/// [advanced by]: differential_dataflow::lattice::Lattice::advance_by
#[allow(clippy::needless_borrow)]
pub fn persist_source_core<'g, G>(
scope: &RefinedScope<'g, G>,
source_id: GlobalId,
persist_clients: Arc<PersistClientCache>,
metadata: CollectionMetadata,
as_of: Option<Antichain<Timestamp>>,
snapshot_mode: SnapshotMode,
until: Antichain<Timestamp>,
map_filter_project: Option<&mut MfpPlan>,
flow_control: Option<FlowControl<RefinedScope<'g, G>>>,
// If Some, an override for the default listen sleep retry parameters.
listen_sleep: Option<impl Fn() -> RetryParameters + 'static>,
start_signal: impl Future<Output = ()> + 'static,
error_handler: impl FnOnce(String) -> Pin<Box<dyn Future<Output = ()>>> + 'static,
) -> (
Stream<
RefinedScope<'g, G>,
(
Result<Row, DataflowError>,
(mz_repr::Timestamp, Subtime),
Diff,
),
>,
Vec<PressOnDropButton>,
)
where
G: Scope<Timestamp = mz_repr::Timestamp>,
{
let cfg = persist_clients.cfg().clone();
let name = source_id.to_string();
let desc = metadata.relation_desc.clone();
let ignores_data = map_filter_project
.as_ref()
.map_or(false, |x| x.ignores_input());
let project = if ignores_data {
ProjectionPushdown::IgnoreAllNonErr {
err_col_name: "err",
key_bytes: SourceData(Ok(Row::default())).encode_to_vec(),
val_bytes: ().encode_to_vec(),
}
} else {
ProjectionPushdown::FetchAll
};
let filter_plan = map_filter_project.as_ref().map(|p| (*p).clone());
let desc_transformer = match flow_control {
Some(flow_control) => Some(move |mut scope: _, descs: &Stream<_, _>, chosen_worker| {
let (stream, token) = backpressure(
&mut scope,
&format!("backpressure({source_id})"),
descs,
flow_control,
chosen_worker,
None,
);
(stream, vec![token])
}),
None => None,
};
let metrics = Arc::clone(persist_clients.metrics());
let filter_name = name.clone();
// The `until` gives us an upper bound on the possible values of `mz_now` this query may see.
// Ranges are inclusive, so it's safe to use the maximum timestamp as the upper bound when
// `until ` is the empty antichain.
let upper = until.as_option().cloned().unwrap_or(Timestamp::MAX);
let (fetched, token) = shard_source(
&mut scope.clone(),
&name,
move || {
let (c, l) = (
Arc::clone(&persist_clients),
metadata.persist_location.clone(),
);
async move { c.open(l).await.unwrap() }
},
metadata.data_shard,
as_of,
snapshot_mode,
until.clone(),
desc_transformer,
Arc::new(metadata.relation_desc),
Arc::new(UnitSchema),
move |stats, frontier| {
let Some(lower) = frontier.as_option().copied() else {
// If the frontier has advanced to the empty antichain,
// we'll never emit any rows from any part.
return false;
};
if lower > upper {
// The frontier timestamp is larger than the until of the dataflow:
// anything from this part will necessarily be filtered out.
return false;
}
let time_range =
ResultSpec::value_between(Datum::MzTimestamp(lower), Datum::MzTimestamp(upper));
if let Some(plan) = &filter_plan {
let metrics = &metrics.pushdown.part_stats;
let stats = RelationPartStats::new(&filter_name, metrics, &desc, stats);
filter_may_match(desc.typ(), time_range, stats, plan)
} else {
true
}
},
listen_sleep,
start_signal,
error_handler,
project,
);
let rows = decode_and_mfp(cfg, &fetched, &name, until, map_filter_project);
(rows, token)
}
fn filter_may_match(
relation_type: &RelationType,
time_range: ResultSpec,
stats: RelationPartStats,
plan: &MfpPlan,
) -> bool {
let arena = RowArena::new();
let mut ranges = ColumnSpecs::new(relation_type, &arena);
ranges.push_unmaterializable(UnmaterializableFunc::MzNow, time_range);
if stats.err_count().into_iter().any(|count| count > 0) {
// If the error collection is nonempty, we always keep the part.
return true;
}
for (id, _) in relation_type.column_types.iter().enumerate() {
let result_spec = stats.col_stats(id, &arena);
ranges.push_column(id, result_spec);
}
let result = ranges.mfp_plan_filter(plan).range;
result.may_contain(Datum::True) || result.may_fail()
}
pub fn decode_and_mfp<G>(
cfg: PersistConfig,
fetched: &Stream<G, FetchedBlob<SourceData, (), Timestamp, Diff>>,
name: &str,
until: Antichain<Timestamp>,
mut map_filter_project: Option<&mut MfpPlan>,
) -> Stream<G, (Result<Row, DataflowError>, G::Timestamp, Diff)>
where
G: Scope<Timestamp = (mz_repr::Timestamp, Subtime)>,
{
let scope = fetched.scope();
let mut builder = OperatorBuilder::new(
format!("persist_source::decode_and_mfp({})", name),
scope.clone(),
);
let operator_info = builder.operator_info();
let mut fetched_input = builder.new_input(fetched, Pipeline);
let (mut updates_output, updates_stream) =
builder.new_output::<ConsolidatingContainerBuilder<_>>();
// Re-used state for processing and building rows.
let mut datum_vec = mz_repr::DatumVec::new();
let mut row_builder = Row::default();
// Extract the MFP if it exists; leave behind an identity MFP in that case.
let map_filter_project = map_filter_project.as_mut().map(|mfp| mfp.take());
builder.build(move |_caps| {
let name = name.to_owned();
// Acquire an activator to reschedule the operator when it has unfinished work.
let activations = scope.activations();
let activator = Activator::new(&operator_info.address[..], activations);
// Maintain a list of work to do
let mut pending_work = std::collections::VecDeque::new();
let mut buffer = Default::default();
move |_frontier| {
fetched_input.for_each(|time, data| {
data.swap(&mut buffer);
let capability = time.retain();
for fetched_blob in buffer.drain(..) {
pending_work.push_back(PendingWork {
capability: capability.clone(),
part: PendingPart::Unparsed(fetched_blob),
})
}
});
// Get dyncfg values once per schedule to amortize the cost of
// loading the atomics.
let yield_fuel = cfg.storage_source_decode_fuel();
let yield_fn = |_, work| work >= yield_fuel;
let optimize_ignored_data_decode = cfg.optimize_ignored_data_decode();
let mut work = 0;
let start_time = Instant::now();
let mut output = updates_output.activate();
while !pending_work.is_empty() && !yield_fn(start_time, work) {
let done = pending_work.front_mut().unwrap().do_work(
&mut work,
&name,
optimize_ignored_data_decode,
start_time,
yield_fn,
&until,
map_filter_project.as_ref(),
&mut datum_vec,
&mut row_builder,
&mut output,
);
if done {
pending_work.pop_front();
}
}
if !pending_work.is_empty() {
activator.activate();
}
}
});
updates_stream
}
/// Pending work to read from fetched parts
struct PendingWork {
/// The time at which the work should happen.
capability: Capability<(mz_repr::Timestamp, Subtime)>,
/// Pending fetched part.
part: PendingPart,
}
enum PendingPart {
Unparsed(FetchedBlob<SourceData, (), Timestamp, Diff>),
Parsed {
part: ShardSourcePart<SourceData, (), Timestamp, Diff>,
error_free: bool,
},
}
impl PendingPart {
/// Returns the contained `FetchedPart`, first parsing it from a
/// `FetchedBlob` if necessary.
///
/// Also returns a bool, which is true if the part is known (from pushdown
/// stats) to be free of `SourceData(Err(_))`s. It will be false if the part
/// is known to contain errors or if it's unknown.
fn part_mut(&mut self) -> (&mut FetchedPart<SourceData, (), Timestamp, Diff>, bool) {
match self {
PendingPart::Unparsed(x) => {
let error_free = error_free(x.stats(), "err").unwrap_or(false);
*self = PendingPart::Parsed {
part: x.parse(),
error_free,
};
// Won't recurse any further.
self.part_mut()
}
PendingPart::Parsed { part, error_free } => (&mut part.part, *error_free),
}
}
}
impl PendingWork {
/// Perform work, reading from the fetched part, decoding, and sending outputs, while checking
/// `yield_fn` whether more fuel is available.
fn do_work<P, YFn>(
&mut self,
work: &mut usize,
name: &str,
optimize_ignored_data_decode: bool,
start_time: Instant,
yield_fn: YFn,
until: &Antichain<Timestamp>,
map_filter_project: Option<&MfpPlan>,
datum_vec: &mut DatumVec,
row_builder: &mut Row,
output: &mut OutputHandleCore<
'_,
(mz_repr::Timestamp, Subtime),
ConsolidatingContainerBuilder<
Vec<(
Result<Row, DataflowError>,
(mz_repr::Timestamp, Subtime),
Diff,
)>,
>,
P,
>,
) -> bool
where
P: Push<
Bundle<
(mz_repr::Timestamp, Subtime),
Vec<(
Result<Row, DataflowError>,
(mz_repr::Timestamp, Subtime),
Diff,
)>,
>,
>,
YFn: Fn(Instant, usize) -> bool,
{
let mut session = output.session_with_builder(&self.capability);
let (fetched_part, part_is_error_free) = self.part.part_mut();
let is_filter_pushdown_audit = fetched_part.is_filter_pushdown_audit();
let mut row_buf = None;
let row_override = map_filter_project
.as_ref()
.map(|p| optimize_ignored_data_decode && part_is_error_free && p.ignores_input())
.unwrap_or(false)
.then(|| (SourceData(Ok(Row::default())), ()));
while let Some(((key, val), time, diff)) =
fetched_part.next_with_storage(&mut row_buf, &mut None, row_override.clone())
{
if until.less_equal(&time) {
continue;
}
match (key, val) {
(Ok(SourceData(Ok(row))), Ok(())) => {
if let Some(mfp) = map_filter_project {
// We originally accounted work as the number of outputs, to give downstream
// operators a chance to reduce down anything we've emitted. This mfp call
// might have a restrictive filter, which would have been counted as no
// work. However, in practice, we've been decode_and_mfp be a source of
// interactivity loss during rehydration, so we now also count each mfp
// evaluation against our fuel.
*work += 1;
let arena = mz_repr::RowArena::new();
let mut datums_local = datum_vec.borrow_with(&row);
for result in mfp.evaluate(
&mut datums_local,
&arena,
time,
diff,
|time| !until.less_equal(time),
row_builder,
) {
if let Some(_stats) = &is_filter_pushdown_audit {
// NB: The tag added by this scope is used for alerting. The panic
// message may be changed arbitrarily, but the tag key and val must
// stay the same.
sentry::with_scope(
|scope| {
scope
.set_tag("alert_id", "persist_pushdown_audit_violation")
},
|| {
// TODO: include more (redacted) information here.
panic!(
"persist filter pushdown correctness violation! {}",
name
);
},
);
}
match result {
Ok((row, time, diff)) => {
// Additional `until` filtering due to temporal filters.
if !until.less_equal(&time) {
let mut emit_time = *self.capability.time();
emit_time.0 = time;
session.give((Ok(row), emit_time, diff));
*work += 1;
}
}
Err((err, time, diff)) => {
// Additional `until` filtering due to temporal filters.
if !until.less_equal(&time) {
let mut emit_time = *self.capability.time();
emit_time.0 = time;
session.give((Err(err), emit_time, diff));
*work += 1;
}
}
}
}
// At the moment, this is the only case where we can re-use the allocs for
// the `SourceData`/`Row` we decoded. This could be improved if this timely
// operator used a different container than `Vec<Row>`.
drop(datums_local);
row_buf.replace(SourceData(Ok(row)));
} else {
let mut emit_time = *self.capability.time();
emit_time.0 = time;
session.give((Ok(row), emit_time, diff));
*work += 1;
}
}
(Ok(SourceData(Err(err))), Ok(())) => {
let mut emit_time = *self.capability.time();
emit_time.0 = time;
session.give((Err(err), emit_time, diff));
*work += 1;
}
// TODO(petrosagg): error handling
(Err(_), Ok(_)) | (Ok(_), Err(_)) | (Err(_), Err(_)) => {
panic!("decoding failed")
}
}
if yield_fn(start_time, *work) {
return false;
}
}
true
}
}
/// A trait representing a type that can be used in `backpressure`.
pub trait Backpressureable: Clone + 'static {
/// Return the weight of the object, in bytes.
fn byte_size(&self) -> usize;
}
impl Backpressureable for (usize, SerdeLeasedBatchPart) {
fn byte_size(&self) -> usize {
self.1.encoded_size_bytes()
}
}
/// Flow control configuration.
#[derive(Debug)]
pub struct FlowControl<G: Scope> {
/// Stream providing in-flight frontier updates.
///
/// As implied by its type, this stream never emits data, only progress updates.
///
/// TODO: Replace `Infallible` with `!` once the latter is stabilized.
pub progress_stream: Stream<G, Infallible>,
/// Maximum number of in-flight bytes.
pub max_inflight_bytes: usize,
/// The minimum range of timestamps (be they granular or not) that must be emitted,
/// ignoring `max_inflight_bytes` to ensure forward progress is made.
pub summary: <G::Timestamp as TimelyTimestamp>::Summary,
/// Optional metrics for the `backpressure` operator to keep up-to-date.
pub metrics: Option<BackpressureMetrics>,
}
/// Apply flow control to the `data` input, based on the given `FlowControl`.
///
/// The `FlowControl` should have a `progress_stream` that is the pristine, unaltered
/// frontier of the downstream operator we want to backpressure from, a `max_inflight_bytes`,
/// and a `summary`. Note that the `data` input expects all the second part of the tuple
/// timestamp to be 0, and all data to be on the `chosen_worker` worker.
///
/// The `summary` represents the _minimum_ range of timestamps that needs to be emitted before
/// reasoning about `max_inflight_bytes`. In practice this means that we may overshoot
/// `max_inflight_bytes`.
///
/// The implementation of this operator is very subtle. Many inline comments have been added.
pub fn backpressure<T, G, O>(
scope: &mut G,
name: &str,
data: &Stream<G, O>,
flow_control: FlowControl<G>,
chosen_worker: usize,
// A probe used to inspect this operator during unit-testing
probe: Option<UnboundedSender<(Antichain<(T, Subtime)>, usize, usize)>>,
) -> (Stream<G, O>, PressOnDropButton)
where
T: TimelyTimestamp + Lattice + Codec64 + TotalOrder,
G: Scope<Timestamp = (T, Subtime)>,
O: Backpressureable + std::fmt::Debug,
{
let worker_index = scope.index();
let (flow_control_stream, flow_control_max_bytes, metrics) = (
flow_control.progress_stream,
flow_control.max_inflight_bytes,
flow_control.metrics,
);
// Both the `flow_control` input and the data input are disconnected from the output. We manually
// manage the output's frontier using a `CapabilitySet`. Note that we also adjust the
// `flow_control` progress stream using the `summary` here, using a `feedback` operator in a
// non-circular fashion.
let (handle, summaried_flow) = scope.feedback(flow_control.summary.clone());
flow_control_stream.connect_loop(handle);
let mut builder = AsyncOperatorBuilder::new(
format!("persist_source_backpressure({})", name),
scope.clone(),
);
let (mut data_output, data_stream) = builder.new_output();
let mut data_input = builder.new_disconnected_input(data, Pipeline);
let mut flow_control_input = builder.new_disconnected_input(&summaried_flow, Pipeline);
// Helper method used to synthesize current and next frontier for ordered times.
fn synthesize_frontiers<T: PartialOrder + Clone>(
mut frontier: Antichain<(T, Subtime)>,
mut time: (T, Subtime),
part_number: &mut u64,
) -> (
(T, Subtime),
Antichain<(T, Subtime)>,
Antichain<(T, Subtime)>,
) {
let mut next_frontier = frontier.clone();
time.1 = Subtime(*part_number);
frontier.insert(time.clone());
*part_number += 1;
let mut next_time = time.clone();
next_time.1 = Subtime(*part_number);
next_frontier.insert(next_time);
(time, frontier, next_frontier)
}
// _Refine_ the data stream by amending the second input with the part number. This also
// ensures that we order the parts by time.
let data_input = async_stream::stream!({
let mut part_number = 0;
let mut parts: Vec<((T, Subtime), O)> = Vec::new();
loop {
match data_input.next().await {
None => {
let empty = Antichain::new();
parts.sort_by_key(|val| val.0.clone());
for (part_time, d) in parts.drain(..) {
let (part_time, frontier, next_frontier) = synthesize_frontiers(
empty.clone(),
part_time.clone(),
&mut part_number,
);
yield Either::Right((part_time, d, frontier, next_frontier))
}
break;
}
Some(Event::Data(time, data)) => {
for d in data {
parts.push((time.clone(), d));
}
}
Some(Event::Progress(prog)) => {
let mut i = 0;
parts.sort_by_key(|val| val.0.clone());
// This can be replaced with `Vec::drain_filter` when it stabilizes.
// `drain_filter_swapping` doesn't work as it reorders the vec.
while i < parts.len() {
if !prog.less_equal(&parts[i].0) {
let (part_time, d) = parts.remove(i);
let (part_time, frontier, next_frontier) = synthesize_frontiers(
prog.clone(),
part_time.clone(),
&mut part_number,
);
yield Either::Right((part_time, d, frontier, next_frontier))
} else {
i += 1;
}
}
yield Either::Left(prog)
}
}
}
});
let shutdown_button = builder.build(move |caps| async move {
// The output capability.
let mut cap_set = CapabilitySet::from_elem(caps.into_element());
// The frontier of our output. This matches the `CapabilitySet` above.
let mut output_frontier = Antichain::from_elem(TimelyTimestamp::minimum());
// The frontier of the `flow_control` input.
let mut flow_control_frontier = Antichain::from_elem(TimelyTimestamp::minimum());
// Parts we have emitted, but have not yet retired (based on the `flow_control` edge).
let mut inflight_parts = Vec::new();
// Parts we have not yet emitted, but do participate in the `input_frontier`.
let mut pending_parts = std::collections::VecDeque::new();
// Only one worker is responsible for distributing parts
if worker_index != chosen_worker {
trace!(
"We are not the chosen worker ({}), exiting...",
chosen_worker
);
return;
}
tokio::pin!(data_input);
'emitting_parts: loop {
// At the beginning of our main loop, we determine the total size of
// inflight parts.
let inflight_bytes: usize = inflight_parts.iter().map(|(_, size)| size).sum();
// There are 2 main cases where we can continue to emit parts:
// - The total emitted bytes is less than `flow_control_max_bytes`.
// - The output frontier is not beyond the `flow_control_frontier`
//
// SUBTLE: in the latter case, we may arbitrarily go into the backpressure `else`
// block, as we wait for progress tracking to keep the `flow_control` frontier
// up-to-date. This is tested in unit-tests.
if inflight_bytes < flow_control_max_bytes
|| !PartialOrder::less_equal(&flow_control_frontier, &output_frontier)
{
let (time, part, next_frontier) =
if let Some((time, part, next_frontier)) = pending_parts.pop_front() {
(time, part, next_frontier)
} else {
match data_input.next().await {
Some(Either::Right((time, part, frontier, next_frontier))) => {
// Downgrade the output frontier to this part's time. This is useful
// "close" timestamp's from previous parts, even if we don't yet
// emit this part. Note that this is safe because `data_input` ensures
// time-ordering.
output_frontier = frontier;
cap_set.downgrade(output_frontier.iter());
// If the most recent value's time is _beyond_ the
// `flow_control` frontier (which takes into account the `summary`), we
// have emitted an entire `summary` worth of data, and can store this
// value for later.
if inflight_bytes >= flow_control_max_bytes
&& !PartialOrder::less_than(
&output_frontier,
&flow_control_frontier,
)
{
pending_parts.push_back((time, part, next_frontier));
continue 'emitting_parts;
}
(time, part, next_frontier)
}
Some(Either::Left(prog)) => {
output_frontier = prog;
cap_set.downgrade(output_frontier.iter());
continue 'emitting_parts;
}
None => {
if pending_parts.is_empty() {
break 'emitting_parts;
} else {
continue 'emitting_parts;
}
}
}
};
let byte_size = part.byte_size();
// Store the value with the _frontier_ the `flow_control_input` must reach
// to retire it. Note that if this `results_in` is `None`, then we
// are at `T::MAX`, and give up on flow_control entirely.
//
// SUBTLE: If we stop storing these parts, we will likely never check the
// `flow_control_input` ever again. This won't pile up data as that input
// only has frontier updates. There may be spurious activations from it though.
//
// Also note that we don't attempt to handle overflowing the `u64` part counter.
if let Some(emission_ts) = flow_control.summary.results_in(&time) {
inflight_parts.push((emission_ts, byte_size));
}
// Emit the data at the given time, and update the frontier and capabilities
// to just beyond the part.
data_output.give(&cap_set.delayed(&time), part);
if let Some(metrics) = &metrics {
metrics.emitted_bytes.inc_by(u64::cast_from(byte_size))
}
output_frontier = next_frontier;
cap_set.downgrade(output_frontier.iter())
} else {
if let Some(metrics) = &metrics {
metrics
.last_backpressured_bytes
.set(u64::cast_from(inflight_bytes))
}
let parts_count = inflight_parts.len();
// We've exhausted our budget, listen for updates to the flow_control
// input's frontier until we free up new budget. If we don't interact with
// with this side of the if statement, because the stream has no data, we
// don't cause unbounded buffering in timely.
let new_flow_control_frontier = match flow_control_input.next().await {
Some(Event::Progress(frontier)) => frontier,
Some(Event::Data(_, _)) => {
unreachable!("flow_control_input should not contain data")
}
None => Antichain::new(),
};
// Update the `flow_control_frontier` if its advanced.
flow_control_frontier.clone_from(&new_flow_control_frontier);
// Retire parts that are processed downstream.
let retired_parts = inflight_parts
.drain_filter_swapping(|(ts, _size)| !flow_control_frontier.less_equal(ts));
let (retired_size, retired_count): (usize, usize) = retired_parts
.fold((0, 0), |(accum_size, accum_count), (_ts, size)| {
(accum_size + size, accum_count + 1)
});
trace!(
"returning {} parts with {} bytes, frontier: {:?}",
retired_count,
retired_size,
flow_control_frontier,
);
if let Some(metrics) = &metrics {
metrics.retired_bytes.inc_by(u64::cast_from(retired_size))
}
// Optionally emit some information for tests to examine.
if let Some(probe) = probe.as_ref() {
let _ = probe.send((new_flow_control_frontier, parts_count, retired_count));
}
}
}
});
(data_stream, shutdown_button.press_on_drop())
}
#[cfg(test)]
mod tests {
use timely::container::CapacityContainerBuilder;
use timely::dataflow::operators::{Enter, Probe};
use tokio::sync::mpsc::unbounded_channel;
use tokio::sync::oneshot;
use super::*;
#[mz_ore::test]
fn test_backpressure_non_granular() {
use Step::*;
backpressure_runner(
vec![(50, Part(101)), (50, Part(102)), (100, Part(1))],
100,
(1, Subtime(0)),
vec![
// Assert we backpressure only after we have emitted
// the entire timestamp.
AssertOutputFrontier((50, Subtime(2))),
AssertBackpressured {
frontier: (1, Subtime(0)),
inflight_parts: 1,
retired_parts: 0,
},
AssertBackpressured {
frontier: (51, Subtime(0)),
inflight_parts: 1,
retired_parts: 0,
},
ProcessXParts(2),
AssertBackpressured {
frontier: (101, Subtime(0)),
inflight_parts: 2,
retired_parts: 2,
},
// Assert we make later progress once processing
// the parts.
AssertOutputFrontier((100, Subtime(3))),
],
true,
);
backpressure_runner(
vec![
(50, Part(10)),
(50, Part(10)),
(51, Part(100)),
(52, Part(1000)),
],
50,
(1, Subtime(0)),
vec![
// Assert we backpressure only after we emitted enough bytes
AssertOutputFrontier((51, Subtime(3))),
AssertBackpressured {
frontier: (1, Subtime(0)),
inflight_parts: 3,
retired_parts: 0,
},
ProcessXParts(3),
AssertBackpressured {
frontier: (52, Subtime(0)),
inflight_parts: 3,
retired_parts: 2,
},
AssertBackpressured {
frontier: (53, Subtime(0)),
inflight_parts: 1,
retired_parts: 1,
},
// Assert we make later progress once processing
// the parts.
AssertOutputFrontier((52, Subtime(4))),
],
true,
);
backpressure_runner(
vec![
(50, Part(98)),
(50, Part(1)),
(51, Part(10)),
(52, Part(100)),
// Additional parts at the same timestamp
(52, Part(10)),
(52, Part(10)),
(52, Part(10)),
(52, Part(100)),
// A later part with a later ts.
(100, Part(100)),
],
100,
(1, Subtime(0)),
vec![
AssertOutputFrontier((51, Subtime(3))),
// Assert we backpressure after we have emitted enough bytes.
// We assert twice here because we get updates as
// `flow_control` progresses from `(0, 0)`->`(0, 1)`-> a real frontier.
AssertBackpressured {
frontier: (1, Subtime(0)),
inflight_parts: 3,
retired_parts: 0,
},
AssertBackpressured {
frontier: (51, Subtime(0)),
inflight_parts: 3,
retired_parts: 0,
},
ProcessXParts(1),
// Our output frontier doesn't move, as the downstream frontier hasn't moved past
// 50.
AssertOutputFrontier((51, Subtime(3))),
// After we process all of `50`, we can start emitting data at `52`, but only until
// we exhaust out budget. We don't need to emit all of `52` because we have emitted
// all of `51`.
ProcessXParts(1),
AssertOutputFrontier((52, Subtime(4))),
AssertBackpressured {
frontier: (52, Subtime(0)),
inflight_parts: 3,
retired_parts: 2,
},
// After processing `50` and `51`, the minimum time is `52`, so we ensure that,
// regardless of byte count, we emit the entire time (but do NOT emit the part at
// time `100`.
ProcessXParts(1),
// Clear the previous `51` part, and start filling up `inflight_parts` with other
// parts at `52`
// This is an intermediate state.
AssertBackpressured {
frontier: (53, Subtime(0)),
inflight_parts: 2,
retired_parts: 1,
},
// After we process all of `52`, we can continue to the next time.
ProcessXParts(5),
AssertBackpressured {
frontier: (101, Subtime(0)),
inflight_parts: 5,
retired_parts: 5,
},
AssertOutputFrontier((100, Subtime(9))),
],
true,
);
}
#[mz_ore::test]
fn test_backpressure_granular() {
use Step::*;
backpressure_runner(
vec![(50, Part(101)), (50, Part(101))],
100,
(0, Subtime(1)),
vec![
// Advance our frontier to outputting a single part.
AssertOutputFrontier((50, Subtime(1))),
// Receive backpressure updates until our frontier is up-to-date but
// not beyond the parts (while considering the summary).
AssertBackpressured {
frontier: (0, Subtime(1)),
inflight_parts: 1,
retired_parts: 0,
},
AssertBackpressured {
frontier: (50, Subtime(1)),
inflight_parts: 1,
retired_parts: 0,
},
// Process that part.
ProcessXParts(1),
// Assert that we clear the backpressure status
AssertBackpressured {
frontier: (50, Subtime(2)),
inflight_parts: 1,
retired_parts: 1,
},
// Ensure we make progress to the next part.
AssertOutputFrontier((50, Subtime(2))),
],
false,
);
backpressure_runner(
vec![
(50, Part(10)),
(50, Part(10)),
(51, Part(35)),
(52, Part(100)),
],
50,
(0, Subtime(1)),
vec![
// we can emit 3 parts before we hit the backpressure limit
AssertOutputFrontier((51, Subtime(3))),
AssertBackpressured {
frontier: (0, Subtime(1)),
inflight_parts: 3,
retired_parts: 0,
},
AssertBackpressured {
frontier: (50, Subtime(1)),
inflight_parts: 3,
retired_parts: 0,
},
// Retire the single part.
ProcessXParts(1),
AssertBackpressured {
frontier: (50, Subtime(2)),
inflight_parts: 3,
retired_parts: 1,
},
// Ensure we make progress, and then
// can retire the next 2 parts.
AssertOutputFrontier((52, Subtime(4))),
ProcessXParts(2),
AssertBackpressured {
frontier: (52, Subtime(4)),
inflight_parts: 3,
retired_parts: 2,
},
],
false,
);
}
type Time = (u64, Subtime);
#[derive(Clone, Debug)]
struct Part(usize);
impl Backpressureable for Part {
fn byte_size(&self) -> usize {
self.0
}
}
/// Actions taken by `backpressure_runner`.
enum Step {
/// Assert that the output frontier of the `backpressure` operator has AT LEAST made it
/// this far. This is a single time because we assume
AssertOutputFrontier(Time),
/// Assert that we have entered the backpressure flow in the `backpressure` operator. This
/// allows us to assert what feedback frontier we got to, and how many inflight parts we
/// retired.
AssertBackpressured {
frontier: Time,
inflight_parts: usize,
retired_parts: usize,
},
/// Process X parts in the downstream operator. This affects the feedback frontier.
ProcessXParts(usize),
}
/// A function that runs the `steps` to ensure that `backpressure` works as expected.
fn backpressure_runner(
// The input data to the `backpressure` operator
input: Vec<(u64, Part)>,
// The maximum inflight bytes the `backpressure` operator allows through.
max_inflight_bytes: usize,
// The feedback summary used by the `backpressure` operator.
summary: Time,
// List of steps to run through.
steps: Vec<Step>,
// Whether or not to consume records in the non-granular scope. This is useful when the
// `summary` is something like `(1, 0)`.
non_granular_consumer: bool,
) {
timely::execute::execute_directly(move |worker| {
let (backpressure_probe, consumer_tx, mut backpressure_status_rx, finalizer_tx, _token) =
// Set up the top-level non-granular scope.
worker.dataflow::<u64, _, _>(|scope| {
let (non_granular_feedback_handle, non_granular_feedback) =
if non_granular_consumer {
let (h, f) = scope.feedback(Default::default());
(Some(h), Some(f))
} else {
(None, None)
};
let (
backpressure_probe,
consumer_tx,
backpressure_status_rx,
token,
backpressured,
finalizer_tx,
) = scope.scoped::<(u64, Subtime), _, _>("hybrid", |scope| {
let (input, finalizer_tx) =
iterator_operator(scope.clone(), input.into_iter());
let (flow_control, granular_feedback_handle) = if non_granular_consumer {
(
FlowControl {
progress_stream: non_granular_feedback.unwrap().enter(scope),
max_inflight_bytes,
summary,
metrics: None
},
None,
)
} else {
let (granular_feedback_handle, granular_feedback) =
scope.feedback(Default::default());
(
FlowControl {
progress_stream: granular_feedback,
max_inflight_bytes,
summary,
metrics: None,
},
Some(granular_feedback_handle),
)
};
let (backpressure_status_tx, backpressure_status_rx) = unbounded_channel();
let (backpressured, token) = backpressure(
scope,
"test",
&input,
flow_control,
0,
Some(backpressure_status_tx),
);
// If we want to granularly consume the output, we setup the consumer here.
let tx = if !non_granular_consumer {
Some(consumer_operator(
scope.clone(),
&backpressured,
granular_feedback_handle.unwrap(),
))
} else {
None
};
(
backpressured.probe(),
tx,
backpressure_status_rx,
token,
backpressured.leave(),
finalizer_tx,
)
});
// If we want to non-granularly consume the output, we setup the consumer here.
let consumer_tx = if non_granular_consumer {
consumer_operator(
scope.clone(),
&backpressured,
non_granular_feedback_handle.unwrap(),
)
} else {
consumer_tx.unwrap()
};
(
backpressure_probe,
consumer_tx,
backpressure_status_rx,
finalizer_tx,
token,
)
});
use Step::*;
for step in steps {
match step {
AssertOutputFrontier(time) => {
eprintln!("checking advance to {time:?}");
backpressure_probe.with_frontier(|front| {
eprintln!("current backpressure output frontier: {front:?}");
});
while backpressure_probe.less_than(&time) {
worker.step();
backpressure_probe.with_frontier(|front| {
eprintln!("current backpressure output frontier: {front:?}");
});
std::thread::sleep(std::time::Duration::from_millis(25));
}
}
ProcessXParts(parts) => {
eprintln!("processing {parts:?} parts");
for _ in 0..parts {
consumer_tx.send(()).unwrap();
}
}
AssertBackpressured {
frontier,
inflight_parts,
retired_parts,
} => {
let frontier = Antichain::from_elem(frontier);
eprintln!(
"asserting backpressured at {frontier:?}, with {inflight_parts:?} inflight parts \
and {retired_parts:?} retired"
);
let (new_frontier, new_count, new_retired_count) = loop {
if let Ok(val) = backpressure_status_rx.try_recv() {
break val;
}
worker.step();
std::thread::sleep(std::time::Duration::from_millis(25));
};
assert_eq!(
(frontier, inflight_parts, retired_parts),
(new_frontier, new_count, new_retired_count)
);
}
}
}
// Send the input to the empty frontier.
let _ = finalizer_tx.send(());
});
}
/// An operator that emits `Part`'s at the specified timestamps. Does not
/// drop its capability until it gets a signal from the `Sender` it returns.
fn iterator_operator<
G: Scope<Timestamp = (u64, Subtime)>,
I: Iterator<Item = (u64, Part)> + 'static,
>(
scope: G,
mut input: I,
) -> (Stream<G, Part>, oneshot::Sender<()>) {
let (finalizer_tx, finalizer_rx) = oneshot::channel();
let mut iterator = AsyncOperatorBuilder::new("iterator".to_string(), scope);
let (mut output_handle, output) =
iterator.new_output::<CapacityContainerBuilder<Vec<Part>>>();
iterator.build(|mut caps| async move {
let mut capability = Some(caps.pop().unwrap());
let mut last = None;
while let Some(element) = input.next() {
let time = element.0.clone();
let part = element.1;
last = Some((time, Subtime(0)));
output_handle.give(&capability.as_ref().unwrap().delayed(&last.unwrap()), part);
}
if let Some(last) = last {
capability
.as_mut()
.unwrap()
.downgrade(&(last.0 + 1, last.1));
}
let _ = finalizer_rx.await;
capability.take();
});
(output, finalizer_tx)
}
/// An operator that consumes its input ONLY when given a signal to do from
/// the `UnboundedSender` it returns. Each `send` corresponds with 1 `Data` event
/// being processed. Also connects the `feedback` handle to its output.
fn consumer_operator<G: Scope, O: Backpressureable + std::fmt::Debug>(
scope: G,
input: &Stream<G, O>,
feedback: timely::dataflow::operators::feedback::Handle<G, Vec<std::convert::Infallible>>,
) -> UnboundedSender<()> {
let (tx, mut rx) = unbounded_channel::<()>();
let mut consumer = AsyncOperatorBuilder::new("consumer".to_string(), scope);
let (output_handle, output) =
consumer.new_output::<CapacityContainerBuilder<Vec<std::convert::Infallible>>>();
let mut input = consumer.new_input_for(input, Pipeline, &output_handle);
consumer.build(|_caps| async move {
while let Some(()) = rx.recv().await {
// Consume exactly one messages (unless the input is exhausted).
while let Some(Event::Progress(_)) = input.next().await {}
}
});
output.connect_loop(feedback);
tx
}
}