Restructure and expand presto_cpp docs

presto-docs/src/main/sphinx/index.rst

@@ -22,7 +22,7 @@ Presto Documentation
     ecosystem
     router
     develop
-    prestissimo
+    presto-cpp
     release
 
 .. Note: If "release" is not the last item, the CSS must be updated.

presto-docs/src/main/sphinx/presto-cpp.rst

@@ -0,0 +1,51 @@
+**********
+Presto C++
+**********
+
+Note: Presto C++ is in active development. See :doc:`Limitations </presto_cpp/limitations>`.
+
+.. toctree::
+    :maxdepth: 1
+
+    presto_cpp/features
+    presto_cpp/limitations
+
+Overview
+========
+
+Presto C++, sometimes referred to by the development name Prestissimo, is a 
+drop-in replacement for Presto workers written in C++ and based on the 
+`Velox <https://velox-lib.io/>`_ library. 
+It implements the same RESTful endpoints as Java workers using the Proxygen C++ 
+HTTP framework. 
+Because communication with the Java coordinator and across workers is only 
+done using the REST endpoints, Presto C++ does not use JNI and does not 
+require a JVM on worker nodes.
+
+Presto C++'s codebase is located at `presto-native-execution
+<https://github.com/prestodb/presto/tree/master/presto-native-execution>`_.
+
+Motivation and Vision
+=====================
+
+Presto aims to be the top performing system for data lakes. 
+To achieve this goal, the Presto community is moving the Presto 
+evaluation engine from the native Java-based implementation to a new 
+implementation written in C++ using `Velox <https://velox-lib.io/>`_.  
+
+By moving the evaluation engine to a library, the intent is to enable the 
+Presto community to focus on more features and better integration with table 
+formats and other data warehousing systems.
+
+Supported Use Cases
+===================
+
+Only specific connectors are supported in the Presto C++ evaluation engine.
+
+* Hive connector for reads and writes, including CTAS, are supported.
+
+* Iceberg tables are supported only for reads.
+
+* Iceberg connector supports both V1 and V2 tables, including tables with delete files.
+
+* TPCH connector, with ``tpch.naming=standard`` catalog property.

presto-docs/src/main/sphinx/prestissimo/prestissimo-features.rst → presto-docs/src/main/sphinx/presto_cpp/features.rst

@@ -1,6 +1,6 @@
-====================
-Prestissimo Features
-====================
+===================
+Presto C++ Features
+===================
 
 .. contents::
     :local:
@@ -27,17 +27,17 @@ Other HTTP endpoints include:
 * GET: v1/info
 * GET: v1/status
 
-The request/response flow of Prestissimo is identical to Java workers. The
+The request/response flow of Presto C++ is identical to Java workers. The
 tasks or new splits are registered via `TaskUpdateRequest`. Resource
 utilization and query progress are sent to the coordinator via task endpoints.
 
 
 Remote Function Execution
 -------------------------
 
-Prestissimo supports remote execution of scalar functions. This feature is
+Presto C++ supports remote execution of scalar functions. This feature is
 useful for cases when the function code is not written in C++, or if for
-security or flexibility reasons the function code cannot be linked to the same
+security or flexibility reasons, the function code cannot be linked to the same
 executable as the main engine.
 
 Remote function signatures need to be provided using a JSON file, following
@@ -114,7 +114,7 @@ function server. If specified, takes precedence over
 JWT authentication support
 --------------------------
 
-Prestissimo supports JWT authentication for internal communication.
+C++ based Presto supports JWT authentication for internal communication.
 For details on the generally supported parameters visit `JWT <../security/internal-communication.html#jwt>`_.
 
 There is also an additional parameter:
@@ -169,9 +169,9 @@ Size of the SSD cache when async data cache is enabled.
 * **Default value:** ``true``
 * **Presto on Spark default value:** ``false``
 
-Enable periodic clean up of old tasks. This is ``true`` for Prestissimo,
-however for Presto on Spark this defaults to ``false`` as zombie/stuck tasks
-are handled by spark via speculative execution.
+Enable periodic clean up of old tasks. The default value is ``true`` for Presto C++. 
+For Presto on Spark this property defaults to ``false``, as zombie or stuck tasks
+are handled by Spark by speculative execution.
 
 ``old-task-cleanup-ms``
 ^^^^^^^^^^^^^^^^^^^^^^^
@@ -189,7 +189,7 @@ Old task is defined as a PrestoTask which has not received heartbeat for at leas
 Session Properties
 ------------------
 
-The following are the native session properties for Prestissimo.
+The following are the native session properties for C++ based Presto.
 
 ``driver_cpu_time_slice_limit_ms``
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

presto-docs/src/main/sphinx/presto_cpp/limitations.rst

@@ -0,0 +1,44 @@
+======================
+Presto C++ Limitations
+======================
+
+.. contents::
+    :local:
+    :backlinks: none
+    :depth: 1
+
+General Limitations
+===================
+
+The C++ evaluation engine has a number of limitations:
+
+* Not all built-in functions are implemented in C++. Attempting to use unimplemented functions results in a query failure. For supported functions, see `Function Coverage <https://facebookincubator.github.io/velox/functions/presto/coverage.html>`_.
+
+* Not all built-in types are implemented in C++. Attempting to use unimplemented types will result in a query failure. 
+
+* Certain parts of the plugin SPI are not used by the C++ evaluation engine. In particular, C++ workers will not load any plugin in the plugins directory, and certain plugin types are either partially or completely unsupported.  
+
+  * ``PageSourceProvider``, ``RecordSetProvider``, and ``PageSinkProvider`` do not work in the C++ evaluation engine.
+
+  * User-supplied functions, types, parametric types and block encodings are not supported.
+
+  * The event listener plugin does not work at the split level.
+
+  * User-defined functions do not work in the same way, see `Remote Function Execution <features.html#remote-function-execution>`_.
+
+* Memory management works differently in the C++ evaluation engine. In particular: 
+
+  * The OOM killer is not supported.
+  * The reserved pool is not supported.
+  * In general, queries may use more memory than they are allowed to through memory arbitration. See `Memory Management <https://facebookincubator.github.io/velox/develop/memory.html>`_.
+
+Functions
+=========
+
+reduce_agg
+----------
+
+In C++ based Presto, ``reduce_agg`` is not permitted to return ``null`` in either the 
+``inputFunction`` or the ``combineFunction``. In Presto (Java), this is permitted 
+but undefined behavior. For more information about ``reduce_agg`` in Presto, 
+see `reduce_agg <../functions/aggregate.html#reduce_agg>`_.