Creating a Stream

You can create a stream using the MapR Control System and the CLI.

Your decision about what streams to create should take into account whatever topics you want to replicate. Replication is between streams, not individual topics.

For example, suppose that you plan to create the stream pollution_monitors to collect various measurements about pollution levels in cities in Europe. However, during a planning session, the representative from Amsterdam says that her country wants to perform analyses of the data for its cities, and would like your company to replicate the data to its own MapR cluster, where its own consumers can read the replicated messages.

You would create a separate stream of topics that contain data from only the pollution sensors in the cities in that country. You might even decide to do the same for each center, in case other centers eventually want to perform their own analyses, too. The streams you might decide to create could be pollution_monitors_netherlands, pollution_monitors_sweden, and so on.

Creating a Stream Using MCS

To create a stream:

  1. Log in to MCS and click Create Stream under Data > Streams.
    The Create New Stream page displays.
  2. Specify the following properties.
    Property Description
    Stream Path The path and name of the stream to create.

    The path to the stream can include any character allowed by MapR. For example, /my/path/with:/to/mystream:topic1 is valid, but /my/path/with:/to/mystream:withcolon:topic1 is invalid.

    The name of the stream cannot include a colon (:) or a forward slash (/).

    Time To Live The amount of time to elapse between the publication of a message in a topic in this stream and the expiration of that message. Choose:
    • Forever to retain messages indefinitely
    • Seconds to specify the number of seconds. A value of 0 causes messages to be retained indefinitely.
    Messages that have expired are deleted during the next purge process. See Time-to-Live for Messages for details.
    Compression The compression setting to use for the stream. Producer client libraries can bundle messages that are to be published on the same partition and compress them. The messages are sent to the server compressed, are stored compressed, are replicated to other containers compressed, and (if stream replication is configured) replicated to replica streams compressed. Consumer client libraries receive compressed data, decompresses it, and passes it to client applications.
    Choose one of the following:
    • Inherited (to inherit from the directory where the stream is stored), which is the default setting
    • OFF (to disable compression)
    • LZF
    • LZF4
    • ZLIB
    Auto Create Topics Whether (Yes) or not (No) to create a topic automatically when a producer tries to write the first message to it.
    Default Partitions The default number of partitions to allocate to new topics in the stream. When deciding how many partitions to create by default for new topics in a stream, consider the expected volume of messages that will be published to the topics in the stream. High message volumes can be handled more efficiently by multiple consumers in consumer groups reading from multiple partitions than by individual consumers reading from a single partition.
    Note: You can override the default and specify a different number of partitions for each topic in the stream at the time of creating the topic or after creating the topic.
    Use for Change Log Whether (Yes) or not (No) to create the stream for changed data records (as a result of inserts, updates, and deletes) in a MapR-DB table.
  3. Set up access to streams for users, groups, and roles.
    For each user, group, and/or role, you can grant (by selecting the associated check box) or block (by deselecting the associated checkbox) the following types of access:
    Administer Can modify the access-control expressions for the stream, set up replication from the stream, and modify attributes of the stream.

    This permission includes the topic permission.

    Copy Stream Can copy data from one MapR stream to another MapR stream (using the mapr copystream utility) and compare the message IDs, metadata, and data in two MapR streams (using the mapr diffstreams utility).
    Topic Can create, edit, or remove topics in the stream.
    Producer Can publish messages to topics in the stream.
    Consumer Can listen to topics in the stream.
    By default, all permissions are given to the user creating the stream. To grant or block access to other users, groups, and/or roles, choose one of the following:
    • Basic Settings: Select the type — public, (OR) user, group, or role — from the drop-down list and grant read and/or write permissions.
      Tip: Click to create a copy of the associated access control setting. Click to remove the associated access control expression.
      Click Add Another to add permissions for another user, group, or role.
    • Advanced Settings: Within empty strings (""), specify user (u), group (g), role (r), or public (p) who have and do not have read and/or write access using the following boolean expressions and subexpressions:
      • ! — Negation operator.
      • & — AND operation.
      • | — OR operation.
      Use (), parentheses, for subexpressions.

      Alternatively, click associated with the type of access to use the Create Access Control Expression window to define access for public or users, group, and/or role.

    Note: If you switch from Basic to Advanced, the basic settings, if any, will be carried over to the Advanced settings. If you switch from Advanced to Basic, all the settings will be lost because the subexpressions and AND (&) and negation (!) operations that are supported by Advanced settings are not supported in the Basic settings.
    To add access control expressions for another user, group, or role, click Add Another and repeat this step.
  4. Click Create Stream to create the stream.

Creating a Stream Using the CLI or REST API

The basic command to create a stream is:

maprcli stream create -path <Stream Path>
To run this command, your user ID must have the following permissions:
  • readAce and writeAce on the volume
  • lookupdir on directories in the path

For complete reference information, see stream create.