Setting the scan_subscriber_queue_size

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Incoming messages are buffered in a queue of the size you can specify via the scan_subscriber_queue_size parameter. The smaller your queue size is, the earlier a message might be processed in a callback (as there are potentially less other messages in the queue that have to be processed before). On the other hand, if callbacks take longer than the time between incoming messages on average, the queue will fill up and messages will eventually be dropped. In that case, there will also be some delay between a message entering the queue and it finally being processed.

We noted that increasing the queue size helps when playing back bagfiles at faster than real-time speeds. If a callback takes longer than normal in that scenario, it can quickly happen that some scan messages are dropped. In normal operation (e.g. using the hokuyo_node directly) the queue size shouldn't have to be increased however.