max_samples

NAME

DDS_ResourceLimitsQosPolicy::max_samples

DESCRIPTION

DDS_ResourceLimitsQosPolicy::max_samples limits the maximum number of samples a DDSDataWriter can allocate and maintain state for at any given time. Every time a write operation is called, a sample is allocated from the cache and filled in with user-data.

A sample allocated from the pool controlled by this resource-limit can be reused based on the following rules:

• If the DDSDataWriter is using DDS_BEST_EFFORT_RELIABILITY_QOS effort the sample is returned for reuse after the transport returns from the write call.
• If the DataWriter is using DDS_RELIABLE_RELIABILITY_QOS and DDS_VOLATILE_DURABILITY_QOS , the sample is returned when all known DataReaders have acknowledged the sample or the DataWriter has given up on delivering the sample (controlled by DDS_RtpsReliableWriterProtocol_t::max_heartbeat_retries), whichever happens first.
• If the DataWriter is using DDS_RELIABLE_RELIABILITY_QOS and not using DDS_VOLATILE_DURABILITY_QOS, the sample is returned to the pool for reuse only if the history depth is exceeded and the DDS_HistoryQosPolicy::kind is set to DDS_KEEP_LAST_HISTORY_QOS

NOTES

For best-effort communication this resource-limit can be set to 1.

For reliable communication the value of this resource-limit determines the maximum number of samples a DDSDataWriter can keep in unacknowledged state before reusing potentially unacknowledged samples (for DDS_KEEP_LAST_HISTORY_QOS). For reliable data the value should take into account the data-rate, the DDS_RtpsReliableWriterProtocol_t::heartbeat_period and DDS_RtpsReliableWriterProtocol_t::heartbeats_per_max_samples.