C++ UDF API

The information below includes all the information one needs to know to begin writing UDFs using the C++ UDF API. For more information on executing C++ UDFs, see Running C++ UDFs.

Dependencies

To begin writing C++ UDFs, access to the Kinetica C++ UDF API is required. In default Kinetica installations, the C++ UDF API is located in the /opt/gpudb/udf/api/cpp directory.

If developing UDFs without a local Kinetica installation, the API can be downloaded from the C++ UDF API repo on GitHub. After downloading, see the README.md in the UDF API directory created for further setup instructions.

The UDF C++ API consists of two files: Proc.hpp & Proc.cpp. These need to be included in the make process and the header file, Proc.hpp needs to be included in the UDF source code. There are no external dependencies beyond the C++ standard library.

To take advantage of GPU processing within a UDF, the CUDA Toolkit must be downloaded & installed from the NVIDIA Developer Zone.

Initializing

A UDF must get a handle to ProcData using kinetica::ProcData::get(). This will parse the primary control file and set up all the necessary structures. It will return a kinetica::ProcData* instance, which is used to access everything else. All configuration information is cached, so repeated calls to kinetica::ProcData::get() will not reload any configuration files.

Important

When you get a handle to ProcData, the handle is actually to the data given to that instance (OS process) of the UDF on the Kinetica host; therefore, there will be a ProcData handle for every instance of the UDF on your Kinetica host

Column Types

Unlike the other Kinetica APIs, the UDF C++ API does not process data using records or schemas, operating in terms of columns of data instead. The raw column values returned closely map to the data types used in the tables being accessed:

Column Category	Column Type	UDF C++ Type
Numeric	int	int32_t
	int8	int8_t
	int16	int16_t
	long	int64_t
	float	float
	double	double
	decimal	int64_t
String	string	char*
	char[N]	char*
	ipv4	uint32_t
Date/Time	date	kinetica::Date
	datetime	kinetica::DateTime
	time	kinetica::Time
	timestamp	int64_t
Binary	bytes	uint8_t*

While CharN column values are arrays of N chars, there is a template class, kinetica::CharN<N>, that makes accessing these easier (it does automatic to and from string conversions and provides accessors that make the chars appear to be in the expected order). To access column values, use:

column.getValue<T>

For example, to retrieve the value for the 10th record as a double:

column.getValue<double>(10)

Note

No type-checking is performed, so the correct type for the column must be used in this call.

Both string & bytes columns are variable-length and are not able to be accessed directly by index. To access string & bytes columns, use these two methods, respectively:

column.getVarString(n)
column.getVarBytes(n)

To determine if a particular value of a nullable column is null, use:

isNull(n)

Calling getValue, getVarString, or getVarBytes on a null value causes undefined behavior, so always check first. Calling isNull on a non-nullable column will always return false.

For debugging purposes, there is also a column.toString(n) method that converts a specified column value to a string, regardless of type.

Reading Input Data

Call	Type	Description
procData->getInputData()	Object	Returns an InputDataSet object for accessing input table data that was passed into the UDF
procData->getRequestInfo()	Map of strings to strings	Returns a map of basic information about the /execute/proc request, map values being accessed using: procData->getRequestInfo().at(<map_key>) The full set of map keys is listed below, under Request Info Keys.
procData->getParams()	Map of strings to strings	Returns a map of string-valued parameters that were passed into the UDF
procData->getBinParams()	Map of strings to bytes	Returns a map of binary-valued parameters that were passed into the UDF

Accessing Input Values

The InputDataSet object returned from procData->getInputData() contains the InputTable object, which in turn contains InputColumn, holding the actual data set. Tables and columns can be accessed by index or by name. For example, given a customer table at InputDataSet index 5 and a name column at that InputTable's index 1, either of the following calls will retrieve the column values associated with customer.name:

procData.getInputData().getTable("customer").getColumn("name")
procData.getInputData().getTable(5).getColumn(1)

Request Info Keys

The request info keys are returned from calling proc_data.request_info. These keys include a variety of details about the executing UDF from the request information map made available to each running UDF.

General Information

Map Key	Description
proc_name	The name of the UDF being executed
run_id	The run ID of the UDF being executed; this is also displayed in GAdmin on the UDF page in the Status section as a link you can click on to get more detailed information; note that although this is an integer, it should not be relied upon as such, as its format may change in the future
rank_number	The processing node container number on which the current UDF instance is executing; for distributed UDFs, [1..n]. For non-distributed UDFs, 0
tom_number	The processing node number within the processing node container on which the current UDF instance is executing; for distributed UDFs, [0..n-1], where n is the number of processing nodes per processing node container. For non-distributed UDFs it is not provided, since these do not run on a processing node
kifs_mount_point	The current mount point for the Kinetica File System (KiFS)
<option_name>	Any options passed in the options map in the /execute/proc request will also be in the request info map

CUDA Information

When executing UDFs that utilize CUDA, additional request information is returned.

Map Key	Description
cuda_devices	The number of CUDA devices currently in use
cuda_free	The amount of CUDA memory available

Data Segment Information

Data is passed into UDFs in segments. Each segment consists of the entirety of the data on a single TOM and is processed by the UDF instance executing on that TOM. Thus, there is a 1-to-1 mapping of data segment and executing UDF instance, though this relationship may change in the future.

Running the same UDF multiple times should result in the same set of segments, assuming the same environment and system state across runs.

Map Key	Description
data_segment_id	A unique identifier for the segment of the currently executing UDF instance; all of the data segment IDs for a given UDF execution are displayed in GAdmin when you click on the run ID; note that although it is possible to identify rank and TOM numbers from this ID, it should not be relied upon, as its format may change in the future
data_segment_count	The total cluster-wide count of data segments for distributed UDFs; for non-distributed UDFs 1
data_segment_number	The number of the current data segment or executing UDF instance [0..data_segment_count-1]

Kinetica API Connection Parameters

These can be used to connect back to Kinetica using the regular API endpoint calls. Use with caution in distributed UDFs, particularly in large clusters, to avoid overwhelming the head node. Also note, multi-head ingest may not work from a UDF in some cases without overriding the worker URLs to use internal IP addresses.

Map Key	Description
head_url	The URL to connect to
username	Randomly generated temporary username used to execute the UDF
password	Randomly generated temporary password used to execute the UDF

Important

Since username and password are randomly generated temporary credentials, which for security reasons should still not be printed or output to logs, etc., as they are live credentials for a period of time.

Writing Output Data

To output data to a table, the size of the table must be set in order to allocate enough space in all of the columns to hold the correct number of values. To do this, call:

table.setSize()

Call	Description
procData->getResults()	Returns a map that can be populated with string-valued results to be returned from the UDF
procData->getBinResults()	Returns a map that can be populated with binary-valued results to be returned from the UDF
procData->getOutputData()	Returns an OutputDataSet object for writing output table data that will be written to the database

Setting Output Values

The OutputDataSet object returned from procData.getOutputData() contains the OutputTable object, which in turn contains OutputColumn, holding the actual data set. Tables and columns are accessed the same way as InputDataSet:

procData->getOutputData().getTable("customer").getColumn("name")
procData->getOutputData().getTable(5).getColumn(1)

There are two approaches to loading values into Kinetica:

• appending a series of values to each table column
• setting table column values by index

The following methods are called on each OutputColumn of the OutputTable:

• Appending (required for variable-length data)
  • appendValue(value)
  • appendVarString(value)
  • appendVarBytes(value)
  • appendNull()
• Setting by Index (non-variable length data only)
  • setValue(n, value)
  • setNull(n, value)

Status Reporting

The procData->getStatus() property can be set to a string value to help convey status information during UDF execution, e.g., procData->getStatus("25% complete"). The /show/proc/status endpoint will return any status messages set for each data segment -- one data segment per processing node if in distributed mode, or one data segment total in non-distributed mode. These messages are subject to the following scenarios:

• If the user-provided UDF code is executing and has set a status message, /show/proc/status will return the last message that was set

• If the user-provided UDF code finishes executing successfully, the status message is cleared

  Note

  The UDF may not show as "complete" yet since any data written by the UDF (in distributed mode) still has to be inserted into the database, but the status set by the UDF code isn't relevant to this process

• If the UDF is killed while executing user-provided UDF code, /show/proc/status will return the last message that was set

• If the user-provided UDF code errors out, /show/proc/status will return the error message and the last status message that was set in parentheses

Complete

The UDF must finish with a call to procData->complete(). This writes out some final control information to indicate that the UDF completed successfully.

Note

If this call is not made, the database will assume that the UDF didn’t finish and will return an error to the caller.

Logging

Any output from the UDF to is written to two places:

• The system log file on the head node
• The /opt/gpudb/core/logs/gpudb_proc.log file local to the processing node container

Logging output location for UDFs is currently not configurable.