Matija Santl a026c4c764 Add test stream clause

Summary:
Added test stream functionality. When a stream is configured, it will try to
consume messages from a kafka topic and return them back to the user.
For now, the messages aren't transformed, so it just returns the payload string.

Depends on D1466

Next steps are persisting stream metadata and transforming messages in order to
store them in the graph.

Reviewers: teon.banek, mtomic

Reviewed By: teon.banek

Subscribers: pullbot, buda

Differential Revision: https://phabricator.memgraph.io/D1474

2018-07-09 11:00:18 +02:00

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Kafka - openCypher clause

One must be able to specify the following when importing data from Kafka:

Kafka URI
Transform script URI

Kafka endpoint is the URI of the leader broker and it is required for data extractor.

Minimum required syntax looks like:

CREATE STREAM kafka_stream AS LOAD DATA KAFKA '127.0.0.1/topic' WITH TRANSFORM
'127.0.0.1/transform.py';

The CREATE STREAM clause happens in a transaction.

The full openCypher clause for creating a stream is:

CREATE STREAM stream_name AS
  LOAD DATA KAFKA 'URI'
  WITH TOPIC 'topic'
  WITH TRANSFORM 'URI'
  [BATCH_INTERVAL milliseconds]
  [BATCH_SIZE count]

The WITH TOPIC parameter specifies the kafka topic from which we'll stream data.

The WITH TRANSFORM parameter should contain a URI of the transform script.

The BATCH_INTERVAL parameter defines the time interval in milliseconds that defines the time between two successive stream importing operations.

The BATCH_SIZE parameter defines the count of kafka messages that will be batched together before import.

If both BATCH_INTERVAL and BATCH_SIZE parameters are given, the condition that is satisfied first will trigger the batched import.

Default values for BATCH_INTERVAL is 100 milliseconds, and the default value for BATCH_SIZE is 10;

The DROP clause deletes a stream:

DROP STREAM stream_name;

The SHOW clause enables you to see all configured streams:

SHOW STREAMS;

You can also start/stop streams with the START and STOP clauses:

START STREAM stream_name [LIMIT count BATCHES];
STOP STREAM stream_name;

A stream needs to be stopped in order to start it and it needs to be started in order to stop it. Starting a started or stopping a stopped stream will not affect that stream.

There are also convenience clauses to start and stop all streams:

START ALL STREAMS;
STOP ALL STREAMS;

Before the actual import, you can also test the stream with the TEST STREAM clause:

TEST STREAM stream_name [LIMIT count BATCHES];

When a stream is tested, data extraction and transformation occurs, but no output is inserted in the graph.

A stream needs to be stopped in order to test it. When the batch limit is omitted, TEST STREAM will run for only one batch by default.

2.3 KiB Raw Blame History

Kafka - openCypher clause

2.3 KiB

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