plcontainer Configuration File

The Greenplum Database utility plcontainer manages the PL/Container configuration files in a Greenplum Database system. The utility ensures that the configuration files are consistent across the Greenplum Database master and segment instances.

Warning: Modifying the configuration files on the segment instances without using the utility might create different, incompatible configurations on different Greenplum Database segments that could cause unexpected behavior.

PL/Container Configuration File

PL/Container maintains a configuration file plcontainer_configuration.xml in the data directory of all Greenplum Database segments. This query lists the Greenplum Database system data directories:

  1. SELECT hostname, datadir FROM gp_segment_configuration;

A sample PL/Container configuration file is in $GPHOME/share/postgresql/plcontainer.

In an XML file, names, such as element and attribute names, and values are case sensitive.

In this XML file, the root element configuration contains one or more runtime elements. You specify the id of the runtime element in the # container: line of a PL/Container function definition.

This is an example file. Note that all XML elements, names, and attributes are case sensitive.

  1. <?xml version="1.0" ?>
  2. <configuration>
  3.     <runtime>
  4.         <id>plc_python_example1</id>
  5.         <image>pivotaldata/plcontainer_python_with_clients:0.1</image>
  6.         <command>./pyclient</command>
  7.     </runtime>
  8.     <runtime>
  9.         <id>plc_python_example2</id>
  10.         <image>pivotaldata/plcontainer_python_without_clients:0.1</image>
  11.         <command>/clientdir/pyclient.sh</command>
  12.         <shared_directory access="ro" container="/clientdir" host="/usr/local/greenplum-db/bin/plcontainer_clients"/>
  13.         <setting memory_mb="512"/>
  14.         <setting use_container_logging="yes"/>
  15.         <setting cpu_share="1024"/>
  16.         <setting resource_group_id="16391"/>
  17.     </runtime>
  18.     <runtime>
  19.         <id>plc_r_example</id>
  20.         <image>pivotaldata/plcontainer_r_without_clients:0.2</image>
  21.         <command>/clientdir/rclient.sh</command>
  22.         <shared_directory access="ro" container="/clientdir" host="/usr/local/greenplum-db/bin/plcontainer_clients"/>
  23.         <setting use_container_logging="yes"/>
  24.         <setting roles="gpadmin,user1"/>
  25.     </runtime>
  26.     <runtime>
  27. </configuration>

These are the XML elements and attributes in a PL/Container configuration file.

configuration

Root element for the XML file.

runtime

One element for each specific container available in the system. These are child elements of the configuration element.

id

Required. The value is used to reference a Docker container from a PL/Container user-defined function. The id value must be unique in the configuration. The id must start with a character or digit (a-z, A-Z, or 0-9) and can contain characters, digits, or the characters _ (underscore), . (period), or - (dash). Maximum length is 63 Bytes.

The id specifies which Docker image to use when PL/Container creates a Docker container to execute a user-defined function.

image

Required. The value is the full Docker image name, including image tag. The same way you specify them for starting this container in Docker. Configuration allows to have many container objects referencing the same image name, this way in Docker they would be represented by identical containers.

For example, you might have two runtime elements, with different id elements, plc_python_128 and plc_python_256, both referencing the Docker image pivotaldata/plcontainer_python:1.0.0. The first runtime specifies a 128MB RAM limit and the second one specifies a 256MB limit that is specified by the memory_mb attribute of a setting element.

command

Required. The value is the command to be run inside of container to start the client process inside in the container. When creating a runtime element, the plcontainer utility adds a command element based on the language (the -l option).

command element for the Python 2 language.

  1. <command>/clientdir/pyclient.sh</command>

command element for the Python 3 language.

  1. <command>/clientdir/pyclient3.sh</command>

command element for the R language.

  1. <command>/clientdir/rclient.sh</command>

You should modify the value only if you build a custom container and want to implement some additional initialization logic before the container starts.

Note: This element cannot be set with the plcontainer utility. You can update the configuration file with the plcontainer runtime-edit command.

shared_directory

Optional. This element specifies a shared Docker shared volume for a container with access information. Multiple shared_directory elements are allowed. Each shared_directory element specifies a single shared volume. XML attributes for the shared_directory element:

  • host - a directory location on the host system.
  • container - a directory location inside of container.
  • access - access level to the host directory, which can be either ro (read-only) or rw (read-write).

When creating a runtime element, the plcontainer utility adds a shared_directory element.

  1. <shared_directory access="ro" container="/clientdir" host="/usr/local/greenplum-db/bin/plcontainer_clients"/>

For each runtime element, the container attribute of the shared_directory elements must be unique. For example, a runtime element cannot have two shared_directory elements with attribute container="/clientdir".

Warning: Allowing read-write access to a host directory requires special consideration.

  • When specifying read-write access to host directory, ensure that the specified host directory has the correct permissions.
  • When running PL/Container user-defined functions, multiple concurrent Docker containers that are running on a host could change data in the host directory. Ensure that the functions support multiple concurrent access to the data in the host directory.

settings

Optional. This element specifies Docker container configuration information. Each setting element contains one attribute. The element attribute specifies logging, memory, or networking information. For example, this element enables logging.

  1. <setting use_container_logging="yes"/>

These are the valid attributes.

  • cpu_share

    Optional. Specify the CPU usage for each PL/Container container in the runtime. The value of the element is a positive integer. The default value is 1024. The value is a relative weighting of CPU usage compared to other containers.

: For example, a container with a cpu_share of 2048 is allocated double the CPU slice time compared with container with the default value of 1024.

  • memory_mb=”size”

    Optional. The value specifies the amount of memory, in MB, that each container is allowed to use. Each container starts with this amount of RAM and twice the amount of swap space. The container memory consumption is limited by the host system cgroups configuration, which means in case of memory overcommit, the container is terminated by the system.

    resource_group_id=”rg_groupid”

    Optional. The value specifies the groupid of the resource group to assign to the PL/Container runtime. The resource group limits the total CPU and memory resource usage for all running containers that share this runtime configuration. You must specify the groupid of the resource group. If you do not assign a resource group to a PL/Container runtime configuration, its container instances are limited only by system resources. For information about managing PL/Container resources, see About PL/Container Resource Management.

    roles=”list_of_roles”

    Optional. The value is a Greenplum Database role name or a comma-separated list of roles. PL/Container runs a container that uses the PL/Container runtime configuration only for the listed roles. If the attribute is not specified, any Greenplum Database role can run an instance of this container runtime configuration. For example, you create a UDF that specifies the plcontainer language and identifies a # container: runtime configuration that has the roles attribute set. When a role (user) runs the UDF, PL/Container checks the list of roles and runs the container only if the role is on the list.

    use_container_logging=”{yes | no}”

    Optional. Activates or deactivates Docker logging for the container. The attribute value yes enables logging. The attribute value no deactivates logging (the default).

: The Greenplum Database server configuration parameter log_min_messages controls the PL/Container log level. The default log level is warning. For information about PL/Container log information, see Notes.

: By default, the PL/Container log information is sent to a system service. On Red Hat 7 or CentOS 7 systems, the log information is sent to the journald service. On Red Hat 6 or CentOS 6 systems, the log is sent to the syslogd service.

Update the PL/Container Configuration

You can add a runtime element to the PL/Container configuration file with the plcontainer runtime-add command. The command options specify information such as the runtime ID, Docker image, and language. You can use the plcontainer runtime-replace command to update an existing runtime element. The utility updates the configuration file on the master and all segment instances.

The PL/Container configuration file can contain multiple runtime elements that reference the same Docker image specified by the XML element image. In the example configuration file, the runtime elements contain id elements named plc_python_128 and plc_python_256, both referencing the Docker container pivotaldata/plcontainer_python:1.0.0. The first runtime element is defined with a 128MB RAM limit and the second one with a 256MB RAM limit.

  1. <configuration>
  2.   <runtime>
  3.     <id>plc_python_128</id>
  4.     <image>pivotaldata/plcontainer_python:1.0.0</image>
  5.     <command>./client</command>
  6.     <shared_directory access="ro" container="/clientdir" host="/usr/local/gpdb/bin/plcontainer_clients"/>
  7.     <setting memory_mb="128"/>
  8.   </runtime>
  9.   <runtime>
  10.     <id>plc_python_256</id>
  11.     <image>pivotaldata/plcontainer_python:1.0.0</image>
  12.     <command>./client</command>
  13.     <shared_directory access="ro" container="/clientdir" host="/usr/local/gpdb/bin/plcontainer_clients"/>
  14.     <setting memory_mb="256"/>
  15.     <setting resource_group_id="16391"/>
  16.   </runtime>
  17. <configuration>

Configuration changes that are made with the utility are applied to the XML files on all Greenplum Database segments. However, PL/Container configurations of currently running sessions use the configuration that existed during session start up. To update the PL/Container configuration in a running session, execute this command in the session.

  1. SELECT * FROM plcontainer_refresh_config;

Running the command executes a PL/Container function that updates the session configuration on the master and segment instances.