This is the process by which consumers consume messages.
Consumers request the MapR Streams consumer client library to check whether any new messages have arrived in the topics or partitions they've subscribed to or the partitions that they've been assigned. Consumers can do this at any time.
If at least a minimum amount of bytes worth of messages is waiting across a consumer's subscription, MapR Streams returns those messages to the consumer up to a maximum amount of bytes. You can configure this minimum and maximum in the configuration parameters for each consumer.
The MapR Streams consumer client library will return messages that have been sent by producers but not yet flushed to disk. If a consumer is able to keep pace with the rate at which a producer publishes messages, consumer client library will consistently return messages from memory, increasing the speed of throughput from producer to consumer.