spaGO v1.0.0-alpha Release NotesRelease Date: 2022-06-14 // 8 months ago
🚀 With this release we introduce breaking changes that bring significant 👌 improvements to the project's structure, API and performance.
It would be difficult and confusing to list every single API change. Instead, the following sections will broadly describe the most relevant changes, arranged by topic.
🚀 Until this release, the project was essentially a monorepo in disguise: the 📦 core packages for handling matrices and computational graphs were accompanied by many models implementations (from the very simple up to the most sophisticated ones) and commands (models management utilities and servers).
We now prefer to keep in this very repository only the core components of spaGO, only enriched with an (opinionated) set of popular models and functionalities. 📦 Bigger sub-packages and related commands are moved to separate repositories. 🚚 The moved content includes, most notably, code related to Transformers and Flair. Please refer to the section Projects using Spago from the README for an ⚡️ updated list of references to separate projects (note: some of them are still 🚧 work in progress). If you have the feeling that something big is missing in spaGO, chances are 🚚 it was moved to one of these separate projects: just have a look there first.
📦 The arrangement of packages has been simplified: there's no need anymore to 📦 distinguish between
pkg; all the main subpackages are located in 📦 the project's root path. Similarly, many packages, previously nested under
pkg/ml, can now be found at root level too.
Go version and dependencies
The minimum required Go version is
1.18, primarily needed for the introduction of type parameters (generics).
Thanks to the creation of separate projects, discussed above, and further 🔨 refactoring, the main set of required dependencies is limited to the ones ✅ for testing.
📦 Only the subpackage
embeddings/store/diskstorerequires something more, so we defined it as "opt-in" submodule, with its own dependencies.
float32 vs. float64
📦 Instead of separate packages
mat64, there is now a single unified 📦 package
mat. Many parts of the implementation make use of type parameters 📦 (generics), however the package's public API makes a rather narrow use of them.
In particular, we abstained from adding type parameters to widely-used types, such as the
Matrixinterface. Where suitable, we are simply favoring
float64values, the de-facto preferred floating point type in Go (just think about Go 📦
mathpackage). For other situations, we introduced a new subpackage
mat/float. It provides simple types, holding either
float64values, as scalars or slices, and makes it easy to convert values between different precisions, all without making explicit use of generics. This design prevents the excessive spreading of type arguments to tons of other 📦 types that need to manipulate matrices, bot from other spaGO packages and from your own code.
- The type
mat.Matrixis the primary interface for matrices and vectors throughout the project.
- The type
mat.Denseis the concrete implementation for a dense matrix. Unlike the interface, it has a type argument to distinguish between
- 🚚 We removed implementation and support for sparse matrices, since their efficacy and utility were marginal. A better implementation might come back in the future.
- A new dense matrix can be created "from scratch" by calling one of the several
NewVecDense, ...). Here you must choose which data type to use, specifying it as type parameter (unless implicit).
- Once you have an existing matrix, you can create new instances preserving
the same data type of the initial one: simply use one of the
New***methods on the matrix instance itself, rather than their top-level function counterparts.
- Any other operation performed on a matrix that creates a new instance will operate with the same type of the receiver, and returns an instance of that type too.
- Operations with matrices of different underlying data types are allowed, just beware the memory and computation overheads introduced by the necessary conversions.
📦 Auto-grad package
- 📦 The package
agnow implicitly works in "define-by-run" mode only. It's way more performant compared to the previous releases, and there would be no significant advantage in re-using a pre-defined graph ("define-and-run").
- There is no
Graphanymore! At least, not as a first citizen: an implicit "virtual" graph is progressively formed each time an operation over some nodes is applied. The virtual graph can be observed by simply walking the tree of operations. Most methods of the former Graph are now simple functions in the
- 🆓 We still provide a way to explicitly "free" some resources after use,
both for helping the garbage collector and for returning some objects
sync.Pool. The function
ag.ReleaseGraphoperates on the virtual graph described above, usually starting from the given output nodes.
- Forward operations are executed concurrently. As soon as an Operator is
created (usually by calling one of the functions in
ag, such as
Prod, etc.), the related Function's
Forwardprocedure is performed on a new goroutine. Nevertheless, it's always safe to ask for the Operator's
Valuewithout worries: if it's called too soon, the function will lock until the result is computed, and only then return the value.
- 🐎 To maximize performance, we removed the possibility to set a custom limit
for concurrent computations. Thanks to the new design, we now let the Go
runtime itself manage this problem for us, so that you can still limit
and finetune concurrency with the
- The implementation of backpropagation is also redesigned and improved.
Instead of invoking the backward procedure on an explicit Graph, you can call
ag.BackwardMany, specifying the output node (or nodes) of your computation (such as loss values, in traditional scenarios). The backward functions traverse the virtual graph and propagate the gradients, leveraging concurrency and making use of goroutines and locks in a way that's very similar to the forward procedure. The backward functions will lock and wait until the whole gradients propagation is complete before returning. The locking mechanism implemented in the nodes'
Gradmethods, will still prevent troubles in case your own code reads the gradients concurrently (that would be very uncommon).
- We also modified the implementation of time-steps handling and truncated
backpropagation. Since we don't have the support of a concrete Graph
structure anymore, we introduced a new dedicated type
ag.TimeStepHandler, and related functions, such as
NodeTimeStep. For performing a truncated backpropagation, we provide the function
ag.BackwardManyT: they work similarly to the normal backpropagation functions described above, only additionally requiring a time-step handler and the desired amount of back steps.
- 💅 We simplified and polished the API for creating new node-variables. Instead
of having multiple functions for simple variables, scalars, constants,
with/without name or grads, and various combination of those, you can now
create any new variable with
ag.Var, which accepts a Matrix value and creates a new node-variable with gradients accumulation disabled by default. To enable gradients propagation, or setting an explicit name (useful for model params or constants), you can use the Variable's chainable methods
WithName. As a shortcut to create a scalar-matrix variable you can use
- 📦 The package
ag/encodingprovides generic structures and functions to obtain a sort of view of a virtual graph, with the goal of facilitating the encoding/marshaling of a graph in various formats. The package
ag/encoding/dotis a rewriting of the former
pkg/ml/graphviz, that uses the
ag/encodingstructures to represent a virtual graph in Graphviz DOT format.
- 📦 As before, package
nnprovides types and functions for defining and handling models. Its subpackages are implementations of most common models. The set of built-in models has been remarkably revisited, moving some of them to separate projects, as previously explained.
Modelinterface has been extremely simplified: it only requires the special empty struct
Moduleto be embedded in a model type. This is necessary only to distinguish an actual model from any other struct, which is especially useful for parameters traversal, or other similar operations.
- 🚚 Since the Graph has been removed from
ag, the models clearly don't need to hold a reference to it anymore. Similarly, there is no need for any other model-specific field, like the ones available from the former
BaseModel. This implies the elimination of some seldomly used properties. Notable examples are the "processing mode" (from the old Graph) and the time step (from the old BaseModel). In situations where a removed value or feature is still needed, we suggest to either reintroduce the missing elements on the models that needs them, or to extract them to separate types and functions. An example of extracted behavior is the handling of time steps, already mentioned in the previous section.
- There is no distinction anymore between "pure" models and processors, making "reification" no longer necessary: once a model is created (or loaded), it can be immediately used, even for multiple concurrent inferences.
- A side effect of removing processor instances is that it's not possible
to hold any sort of state related to a specific inference inside the
structure of a model (or, at least, it's discouraged in most situations).
Keeping track of a state is quite common for models that work with a running
"memory" or cache. The recommended approach is to represent the state
as a separate type, so that the "old" state can be passed as argument
to the model's forward function (along with any other input), and the "new"
or updated state can be returned from the same function (along with any other
Some good examples can be observed in the implementation of recurrent
networks (RNNs), located at
nn/recurrent/...: each model has a single-step forward function (usually called
Next) that accepts a previous state and returns a new one.
- 🚚 We removed the
StackModel, in favor of a new simple function
nn.Forward, that operates on a slice of
StandardModelinterfaces, connecting outputs to inputs sequentially for each module.
- We introduced the new type
nn.Buffer: it's a Node implementation that does not require gradients, but can be serialized just like any other parameter. This is useful, for example, to store constants, to track the mean and std in batch norm layers, etc. As a shortcut to create a Buffer with a scalar-matrix value you can use
- 🔨 We refactored the arguments of the parameters-traversal functions
ForEachParamStrict. Furthermore, the new interface
ParamsTraverserallows to traverse a model's parameters that are not automatically discovered by the traversal functions via reflection. If a model implements this interface, the function
TraverseParamswill take precedence over the regular parameters visit.
- We introduced the function
Apply, which visits all sub-models of any Model. Typical usages of this function include parameters initialization.
- 🔨 The embeddings model has been refactored and made more flexible by splitting the new implementation into three main concerns: stores, the actual model, and the model's parameters.
- Raw embeddings data can be read from, and perhaps written to,
virtually any suitable medium, be it in-memory, on-disk, local or remote
services or databases, etc. The
Storeinterface, defined in package
embeddings/store, only requires an implementation to implement a bunch of read/write functions for key/value pairs. Both keys and values are just slice of bytes. For example, in a typical scenario involving word embeddings, a key might be a
stringword converted to
byte, and the value the byte-marshaled representation of a vector (or a more complex struct also holding other properties).
- It's not uncommon for a complex model, or application, to make use of
more than one store. For a more convenient handling, multiple independent
Stores can be organized together in a
Repository, another interface defined in
embeddings/store. A Repository is simply a provider for Stores, where each Store is identified by a
stringname. For example, if we are going to use a relational database for storing embeddings data, the Repository might establish the connection to the database, whereas each Store might identify a separate table by name, used for reading/writing data.
- We provide two built-in implementations of Repository/Store pairs.
embeddings/store/diskstoreis a Go submodule that stores data on disk, using BadgerDB; this is comparable to the implementation from previous releases. The package
embeddings/store/memstoreis a simple volatile in-memory implementation; among other usages, it might be especially convenient for testing.
- 📦 The package
embeddingsimplements the main embeddings
Model. One Model can read and write data to a single Store, obtained from a Repository by the configured name. The model delegates to the embeddings Store the responsibility to actually store the data; for this reason, the Store value on a Model is prevented from being serialized (this is done with the utility type
- To facilitate different use cases, the Model allows a limited set of
possible key types, using the constraint
Keyas type argument.
- The type
Embeddingrepresents a single embedding value that can be handled by a Model. It satisfies the interface
nn.Param, allowing seamless integration with operations involving any other model. Behind the hood, the implementation takes care of reading/writing data against a Store, efficiently handling marshaling/unmarshaling and preventing race conditions. The
Payload(if any) are read/written against the Store; the
Gradis only kept in memory. All properties of different
Embeddinginstances for the same key are kept synchronized upon changes.
- A Model keeps track of all Embedding parameters with associated gradients.
TraverseParamsallows these parameters to be discovered and seen as if they were any other regular type of parameter. This is especially important for operations such as embeddings optimization.
- It is a common practice to share the same embeddings among multiple models.
In this case it is important that the serialized (and deserialized)
instance is very same one. Therefore, we introduced the
Sharedstructure that prevents binary marshaling.
- 📦 Gradient descent optimization algorithms are available under the package
gd, with minor API changes.
- 🚚 We removed other methods, such as differential evolution, planning to re-implement them on separate forthcoming projects.
- 📦 We removed the formed package
pkg/utils. Some of its content was related to functionalities now moved to separate projects. Any remaining useful code has been refactored and moved to more appropriate places.
- The type
Previous changes from v0.7.0
- 🆕 New package
ml/ag/encoding/dot, for simple serialization of a Graph to DOT (Graphviz) format.
- 🆕 New package
ml/nn/sgu, implementing a Spatial Gating Unit (SGU) model.
- 🆕 New package
ml/nn/conv1x1, implementing a simple 1-dimensional 1-sized-kernel convolution model.
- 🆕 New package
ml/nn/gmlp, implementing a gMLP model.
ml/nn/activation/Model.Forwardnow simply returns the input as it is if the activation function is the identity.
- 🆕 New package