CHANGELOG.md

Changelog

All notable changes to this project will be documented in this file.

0.12.0

The Timestamp trait has a new method minimim() that replaces Timely's use of Default::default() for default capabilities. The most pressing reason for this is the use of signed integers for timestamps, where Timely would effectively prevent the use of negative numbers by providing the default value of zero for capabilities. This should not have reduced any functionality, but might provide surprising output for programs that use integer timestamps and do not first advance timestamps (the tidy 0 will be replaced with _::min_value()).

Added

Timely configuration can now be done with the worker::Config type, which supports user-defined configuration options. The get and set methods allow binding arbitrary strings to arbitrary types T: Send + Sync + 'static. For example, differential dataflow uses this mechanism to configure its background compaction rates.

Removed

Removed all deprecated methods and traits.

Timely no longer responds to the DEFAULT_PROGRESS_MODE environment variable. Instead, it uses the newly added worker::Config.

Removed the sort crate, whose sorting methods are interesting but not currently a core part of timely dataflow.

Changed

The default progress mode changed from "eager" to "demand driven", which causes progress updates to be accumulated for longer before transmission. The eager default had the potential to produce catastrophically large volumes of progress update messages, for the benefit of a reduced critical path latency. The demand-driven default removes the potential for catastrophic failure at the expense of an increase minimal latency. This should give a better default experience as one scales up the to large numbers of workers.

0.11.0

Reduce the amount of log flushing, and increase the batching of log messages.

0.10.0

Added

A Worker now has a step_or_park(Option<Duration>) method, which instructs the worker to take a step and gives it permission to park the worker thread for at most the supplied timeout if there is no work to perform. A value of None implies no timeout (unboundedly parked) whereas a value of Some(0) should return immediately. The communication layers are implemented to awaken workers if they receive new communications, and workers should hand out copies of their Thread if they want other threads to wake them for other reasons (e.g. queues from threads external to timely).

Communication WorkerGuards expose their underlying join handles to allow the main thread or others to unpark worker threads that may be parked (for example, after pushing new data into a queue shared with the worker).

0.9.0

Added

The OperatorInfo struct now contains the full address of the operator as a Vec<usize>.

Changed

The source operator requires a closure that accepts an OperatorInfo struct in addition to its initial capability. This brings it to parity with the other closure-based operators, and is required to provide address information to the operator.

The address associated with each operator, a [usize] used to start with the identifier of the worker hosting the operator, followed by the dataflow identifier and the path down the dataflow to the operator. The worker identifier has been removed.

The Worker and the Subgraph operator no longer schedules all of their child dataflows and scopes by default. Instead, they track "active" children and schedule only those. Operators become active by receiving a message, a progress update, or by explicit activation. Some operators, source as source, have no inputs and will require explicit activation to run more than once. Operators that yield before completing all of their work (good for you!) should explicitly re-activate themselves to ensure they are re-scheduled even if they receive no further messages or progress updates. Documentation examples for the source method demonstrate this.

The dataflow_using method has been generalized to support arbitrary dataflow names, loggers, and additional resources the dataflow should keep alive. Its name has been changed to dataflow_core.

You can now construct feedback operators with a Default::default() path summary, which has the ability to not increment timestamps. Instead of panicking, Timely's reachability module will inform you if a non-incrementing cycle is detected, at which point you should probably double check your code. It is not 100% known what the system will do in this case (e.g., the progress tracker may enter a non-terminating loop; this is on you, not us ;)).

0.8.0

This release made several breaking modifications to the types associated with scopes, and in particular the generic parameters for the Child<'a, G: ScopeParent, T: Timestamp> type. Where previously the T parameter would be the new coordinate to add to G's timestamp, it is now the new timestamp including G's timestamp as well. This was done to support a broader class of timestamps to be used, beyond always requiring product combinations with new timestamps.

Beneficial fallouts include our ability to remove RootTimestamp, as dataflows can now be timestamped by usize or other primitive timestamps. Yay!

Added

• The communication crate now has a bincode feature flag which should swing serialization over to use serde's Serialize trait. While it seems to work the ergonomics are likely in flux, as the choice is crate-wide and doesn't allow you to pick and choose a la carte.

• Timestamps may now implement a new Refines trait which allows one to describe one timestamp as a refinement of another. This is mainly used to describe which timestamps may be used for subscopes of an outer scope. The trait describes how to move between the timestamps (informally: "adding a zero" and "removing the inner coordinate") and how to summarize path summaries for the refining timestamp as those of the refined timestamp.

Changed

• Many logging events have been rationalized. Operators and Channels should all have a worker-unique identifier that can be used to connect their metadata with events involving them. Previously this was a bit of a shambles.

• The Scope method scoped now allows new scopes with non-Product timestamps. Instead, the new timestamp must implement Refines<_> of the parent timestamp. This is the case for Product timestamps, but each timestamp also refines itself (allowing logical regions w/o changing the timestamp), and other timestamp combinators (e.g. Lexicographic) can be used.

• Root dataflow timestamps no longer need to be Product<RootTimestamp,_>. Instead, the _ can be used as the timestamp.

• The loop_variable operator now takes a timestamp summary for the timestamp of its scope, not just the timestamp extending its parent scope. The old behavior can be recovered with Product::new(Default::default(), summary), but the change allows cycles in more general scopes and seemed worth it. The operator also no longer takes a limit, and if you need to impose a limit other than the summary returning None you should use the branch_when operator.

Removed

• The RootTimestamp and RootSummary types have been excised. Where you previously used Product<RootTimestamp,T> you can now use Product<(),T>, or even better just T. The requirement of a worker's dataflow() method is that the timestamp type implement Refines<()>, which .. ideally would be true for all timestamps but we can't have a blanket implementation until specialization lands (I believe).

• Several race conditions were "removed" from the communication library. These mostly involved rapid construction of dataflows (data received before a channel was constructed would be dropped) and clean shutdown (a timely computation could drop and fail to ack clean shutdown messages).

0.7.0

Added

• You can now construct your own vector of allocator builders and supply them directly to timely::execute::execute_from. Previously one was restricted to whatever a Configuration could provide for you. This should allow more pleasant construction of custom allocators, or custom construction of existing allocators.
• Each timely worker now has a log registry, worker.log_registry(), from which you can register and acquire typed loggers for named log streams. This supports user-level logging, as well as user-configurable timely logging. Timely logging is under the name "timely".

Changed

• The Root type has been renamed Worker and is found in the ::worker module. The methods of the ScopeParent trait are now in the ::worker::AsWorker trait.
• The communication Allocate trait's main method allocate now takes a worker-unique identifier to use for the channel. The allocator may or may not use the information (most often for logging), but they are allowed to be incorrect if one allocates two channels with the same identifier.
• A CapabilityRef<T> now supports retain_for(usize) which indicates a specific output port the capability should be retain for use with. The retain() method still exists for now and is equivalent to retain(0). This change also comes with the inability to use an arbitrary Capability<T> with any output; using a capability bound to the wrong output will result in a run-time error.
• The unary and binary operators now provide data as a RefOrMut, which does not implement DerefMut. More information on how to port methods can be found here.

Removed

• The deprecated Unary and Binary operator extension traits have been removed in favor of the Operator trait that supports both of them, as well as their _notify variants.