docs: Fix docs for Go feature retrieval (#2967)

* Docs

Signed-off-by: Felix Wang <[email protected]>

* Update production docs

Signed-off-by: Felix Wang <[email protected]>

* Update page name

Signed-off-by: Felix Wang <[email protected]>

* Update roadmap

Signed-off-by: Felix Wang <[email protected]>

Author: felixwang9817

docs/SUMMARY.md

@@ -51,7 +51,6 @@
   * [Load data into the online store](how-to-guides/feast-snowflake-gcp-aws/load-data-into-the-online-store.md)
   * [Read features from the online store](how-to-guides/feast-snowflake-gcp-aws/read-features-from-the-online-store.md)
 * [Running Feast in production](how-to-guides/running-feast-in-production.md)
-* [Deploying a Java feature server on Kubernetes](how-to-guides/fetching-java-features-k8s.md)
 * [Upgrading from Feast 0.9](https://docs.google.com/document/u/1/d/1AOsr\_baczuARjCpmZgVd8mCqTF4AZ49OEyU4Cn-uTT0/edit)
 * [Adding a custom provider](how-to-guides/creating-a-custom-provider.md)
 * [Adding a custom batch materialization engine](how-to-guides/creating-a-custom-materialization-engine.md)
@@ -93,7 +92,7 @@
   * [.feastignore](reference/feature-repository/feast-ignore.md)
 * [Feature servers](reference/feature-servers/README.md)
   * [Python feature server](reference/feature-servers/python-feature-server.md)
-  * [Go-based feature retrieval](reference/feature-servers/go-feature-retrieval.md)
+  * [Go feature server](reference/feature-servers/go-feature-server.md)
 * [\[Alpha\] Web UI](reference/alpha-web-ui.md)
 * [\[Alpha\] Data quality monitoring](reference/dqm.md)
 * [\[Alpha\] On demand feature view](reference/alpha-on-demand-feature-view.md)

docs/how-to-guides/fetching-java-features-k8s.md

@@ -242,14 +242,12 @@ This service will provide an HTTP API with JSON I/O, which can be easily used wi
 
 [Read more about this feature](../reference/alpha-aws-lambda-feature-server.md)
 
-### 4.3. Java based Feature Server deployed on Kubernetes
+### 4.3. Go feature server deployed on Kubernetes
 
-For users with very latency-sensitive and high QPS use-cases, Feast offers a high-performance Java feature server.
-Besides the benefits of running on JVM, this implementation also provides a gRPC API, which guarantees good connection utilization and
-small request / response body size (compared to JSON).
-You will need the Feast Java SDK to retrieve features from this service. This SDK wraps all the gRPC logic for you and provides more convenient APIs.
+For users with very latency-sensitive and high QPS use-cases, Feast offers a high-performance [Go feature server](../reference/feature-servers/go-feature-server.md).
+It can use either HTTP or gRPC.
 
-The Java based feature server can be deployed to Kubernetes cluster via Helm charts in a few simple steps:
+The Go feature server can be deployed to a Kubernetes cluster via Helm charts in a few simple steps:
 
 1. Install [kubectl](https://kubernetes.io/docs/tasks/tools/install-kubectl/) and [helm 3](https://helm.sh/)
 2. Add the Feast Helm repository and download the latest charts:
@@ -259,17 +257,19 @@ helm repo update
 ```
 3. Run Helm Install
 ```
-helm install feast-release feast-charts/feast \
+helm install feast-release feast-charts/feast-python-server \
     --set global.registry.path=s3://feast/registries/prod \
     --set global.project=<project name>
 ```
 
-This chart will deploy two services: `feature-server` and `transformation-service`.
-Both must have read access to the registry file on cloud storage. Both will keep a copy of the registry in their memory and periodically refresh it, so expect some delays in update propagation in exchange for better performance.
+This chart will deploy a single service.
+The service must have read access to the registry file on cloud storage.
+It will keep a copy of the registry in their memory and periodically refresh it, so expect some delays in update propagation in exchange for better performance.
+In order for the Go feature server to be enabled, you should set `go_feature_serving: True` in the `feature_store.yaml`.
 
 #### Load balancing
 
-The next step would be to install an L7 Load Balancer (eg, [Envoy](https://www.envoyproxy.io/)) in front of the Java feature server.
+The next step would be to install an L7 Load Balancer (eg, [Envoy](https://www.envoyproxy.io/)) in front of the Go feature server.
 For seamless integration with Kubernetes (including services created by Feast Helm chart) we recommend using [Istio](https://istio.io/) as Envoy's orchestrator.
 
 ## 5. Ingesting features from a stream source
@@ -344,8 +344,8 @@ Summarizing it all together we want to show several options of architecture that
 * Feast SDK is being triggered by CI (eg, Github Actions). It applies the latest changes from the feature repo to the Feast registry
 * Airflow manages materialization jobs to ingest data from DWH to the online store periodically
 * For the stream ingestion Feast Python SDK is used in the existing Spark / Beam pipeline
-* Online features are served via either a Python feature server or a high performance Java feature server
-  * Both the Java feature server and the transformation server are deployed on Kubernetes cluster (via Helm charts)
+* Online features are served via either a Python feature server or a high performance Go feature server
+  * The Go feature server can be deployed on a Kubernetes cluster (via Helm charts)
 * Feast Python SDK is called locally to generate a training dataset
 
 ![From Repository to Production: Feast Production Architecture](production-spark.png)

docs/how-to-guides/running-feast-in-production.md

@@ -0,0 +1,93 @@
+# Go feature server
+
+## Overview
+
+The Go feature server is an HTTP/gRPC endpoint that serves features.
+It is written in Go, and is therefore significantly faster than the Python feature server.
+See this [blog post](https://feast.dev/blog/go-feature-server-benchmarks/) for more details on the comparison between Python and Go.
+In general, we recommend the Go feature server for all production use cases that require extremely low-latency feature serving.
+Currently only the Redis and SQLite online stores are supported.
+
+## CLI
+
+By default, the Go feature server is turned off.
+To turn it on you can add `go_feature_serving: True` to your `feature_store.yaml`:
+
+{% code title="feature_store.yaml" %}
+```yaml
+project: my_feature_repo
+registry: data/registry.db
+provider: local
+online_store:
+  type: redis
+  connection_string: "localhost:6379"
+go_feature_serving: True
+```
+{% endcode %}
+
+Then the `feast serve` CLI command will start the Go feature server.
+As with Python, the Go feature server uses port 6566 by default; the port be overridden with a `--port` flag.
+Moreover, the server uses HTTP by default, but can be set to use gRPC with `--type=grpc`.
+
+Alternatively, if you wish to experiment with the Go feature server instead of permanently turning it on, you can just run `feast serve --go`.
+
+## Installation
+
+The Go component comes pre-compiled when you install Feast with Python versions 3.8-3.10 on macOS or Linux (on x86).
+In order to install the additional Python dependencies, you should install Feast with
+```
+pip install feast[go]
+```
+You must also install the Apache Arrow C++ libraries.
+This is because the Go feature server uses the cgo memory allocator from the Apache Arrow C++ library for interoperability between Go and Python, to prevent memory from being accidentally garbage collected when executing on-demand feature views.
+You can read more about the usage of the cgo memory allocator in these [docs](https://pkg.go.dev/github.com/apache/arrow/go/[email protected]/cdata#ExportArrowRecordBatch).
+
+For macOS, run `brew install apache-arrow`.
+For linux users, you have to install `libarrow-dev`.
+```
+sudo apt update
+sudo apt install -y -V ca-certificates lsb-release wget
+wget https://apache.jfrog.io/artifactory/arrow/$(lsb_release --id --short | tr 'A-Z' 'a-z')/apache-arrow-apt-source-latest-$(lsb_release --codename --short).deb
+sudo apt install -y -V ./apache-arrow-apt-source-latest-$(lsb_release --codename --short).deb
+sudo apt update
+sudo apt install -y -V libarrow-dev # For C++
+```
+For developers, if you want to build from source, run `make compile-go-lib` to build and compile the go server. In order to build the go binaries, you will need to install the `apache-arrow` c++ libraries.
+
+## Alpha features
+
+### Feature logging
+
+The Go feature server can log all requested entities and served features to a configured destination inside an offline store.
+This allows users to create new datasets from features served online. Those datasets could be used for future trainings or for
+feature validations. To enable feature logging we need to edit `feature_store.yaml`:
+```yaml
+project: my_feature_repo
+registry: data/registry.db
+provider: local
+online_store:
+  type: redis
+  connection_string: "localhost:6379"
+go_feature_serving: True
+feature_server:
+  feature_logging:
+    enable: True
+```
+
+Feature logging configuration in `feature_store.yaml` also allows to tweak some low-level parameters to achieve the best performance:
+```yaml
+feature_server:
+  feature_logging:
+    enable: True
+    flush_interval_secs: 300
+    write_to_disk_interval_secs: 30
+    emit_timeout_micro_secs: 10000
+    queue_capacity: 10000
+```
+All these parameters are optional.
+
+### Python SDK retrieval
+
+The logic for the Go feature server can also be used to retrieve features during a Python `get_online_features` call.
+To enable this behavior, you must add `go_feature_retrieval: True` to your `feature_store.yaml`.
+You must also have all the dependencies installed as detailed above.

docs/reference/feature-servers/go-feature-retrieval.md

@@ -2,23 +2,22 @@
 
 ## Overview
 
-The feature server is an HTTP endpoint that serves features with JSON I/O. This enables users to write + read features from Feast online stores using any programming language that can make HTTP requests.
+The Python feature server is an HTTP endpoint that serves features with JSON I/O. This enables users to write and read features from the online store using any programming language that can make HTTP requests.
 
 ## CLI
 
-There is a CLI command that starts the server: `feast serve`. By default, Feast uses port 6566; the port be overridden by a `--port` flag.
+There is a CLI command that starts the server: `feast serve`. By default, Feast uses port 6566; the port be overridden with a `--port` flag.
 
 ## Deploying as a service
 
-One can also deploy a feature server by building a docker image that bundles in the project's `feature_store.yaml`. See [helm chart](https://github.com/feast-dev/feast/blob/master/infra/charts/feast-python-server) for example.
-
-A [remote feature server](../alpha-aws-lambda-feature-server.md) on AWS Lambda is available. A remote feature server on GCP Cloud Run is currently being developed.
+One can deploy a feature server by building a docker image that bundles in the project's `feature_store.yaml`. See this [helm chart](https://github.com/feast-dev/feast/blob/master/infra/charts/feast-python-server) for an example.
 
+A [remote feature server](../alpha-aws-lambda-feature-server.md) on AWS Lambda is also available.
 
 ## Example
 
 ### Initializing a feature server
-Here's the local feature server usage example with the local template:
+Here's an example of how to start the Python feature server with a local feature repo:
 
 ```bash
 $ feast init feature_repo
@@ -27,9 +26,11 @@ Creating a new Feast repository in /home/tsotne/feast/feature_repo.
 $ cd feature_repo
 
 $ feast apply
-Registered entity driver_id
-Registered feature view driver_hourly_stats
-Deploying infrastructure for driver_hourly_stats
+Created entity driver
+Created feature view driver_hourly_stats
+Created feature service driver_activity
+
+Created sqlite table feature_repo_driver_hourly_stats
 
 $ feast materialize-incremental $(date +%Y-%m-%d)
 Materializing 1 feature views to 2021-09-09 17:00:00-07:00 into the sqlite online store.
@@ -38,8 +39,6 @@ driver_hourly_stats from 2021-09-09 16:51:08-07:00 to 2021-09-09 17:00:00-07:00:
 100%|████████████████████████████████████████████████████████████████| 5/5 [00:00<00:00, 295.24it/s]
 
 $ feast serve
-This is an experimental feature. It's intended for early testing and feedback, and could change without warnings in future releases.
-INFO:     Started server process [8889]
 09/10/2021 10:42:11 AM INFO:Started server process [8889]
 INFO:     Waiting for application startup.
 09/10/2021 10:42:11 AM INFO:Waiting for application startup.
@@ -49,7 +48,7 @@ INFO:     Uvicorn running on http://127.0.0.1:6566 (Press CTRL+C to quit)
 09/10/2021 10:42:11 AM INFO:Uvicorn running on http://127.0.0.1:6566 (Press CTRL+C to quit)
 ```
 
-### Retrieving features from the online store
+### Retrieving features
 After the server starts, we can execute cURL commands from another terminal tab:
 
 ```bash
@@ -153,11 +152,9 @@ curl -X POST \
 ```
 
 ### Pushing features to the online and offline stores
-You can push data corresponding to a push source to the online and offline stores (note that timestamps need to be strings):
-
-You can also define a pushmode to push stream or batch data, either to the online store, offline store, or both. The feature server will throw an error if the online/offline store doesn't support the push api functionality.
+The Python feature server also exposes an endpoint for [push sources](../../data-sources/push.md). This endpoint allows you to push data to the online and/or offline store.
 
-The request definition for pushmode is a string parameter `to` where the options are: ["online", "offline", "online_and_offline"].
+The request definition for pushmode is a string parameter `to` where the options are: ["online", "offline", "online_and_offline"]. Note that timestamps need to be strings.
 ```text
 curl -X POST "http://localhost:6566/push" -d '{
     "push_source_name": "driver_hourly_stats_push_source",