The DDS samples received and stored by the PRSTDataReaders and PRSTDataWriters are in serialized form.
The serialized size of a DDS sample is the number of bytes required to send the DDS sample on the wire. The maximum serialized size of a DDS sample is the number of bytes that the largest DDS sample for a given type requires on the wire.
By default, the PRSTDataReaders and PRSTDataWriters created by the persistence service try to allocate multiple DDS samples to their maximum serialized size. This may cause memory allocation issues when the maximum serialized size is significantly large.
For PRSTDataReaders, the number of DDS samples in the DataReader’s queues can be controlled using the QoS values resource_qos.resource_limits.max_samples and resource_qos.resource_limits.initial_samples.
The PRSTDataWriters keep a cache of DDS samples so that they do not have to access the database every time. The minimum size of this cache is 32 DDS samples.
In addition, each PRSTDataWriter keeps an additional DDS sample called the DB sample, which is used to move information from the DataWriter cache to the database and vice versa
The <memory_management> tag in a persistence group can be used to control the memory allocation policy for the DDS samples created by PRSTDataReaders and PRSTDataWriters in the persistence group.
Memory Management Tags describes the memory management tags.
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Tags within |
Description |
Number of Tags Allowed |
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<persistent_sample_ |
This tag is used to control the memory associated with the DB sample in a PRSTDataWriter. The persistence service will not be able to store a DDS sample into persistent storage if the serialized size is greater than this value. Therefore, this parameter must be used carefully. Default: LENGTH_UNLIMITED (DB sample is allocated to the maximum size). |
0 or 1 |
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<pool_sample_ |
This tag applies to both PRSTDataReaders and PRSTDataWriters. Its value determines the maximum size (in bytes) of the buffers that will be pre-allocated to store the DDS samples. If the space required for a new DDS sample is greater than this size, the persistence service will allocate the memory dynamically to the exact size required by the DDS sample. This parameter is used to control the memory allocated for the DDS samples in the PRSTDataReaders queues and the PRSTDataWriters caches. The size of the DB sample in the PRSTDataWriters is controlled by the value of the tag <persistent_sample_buffer_max_size>. Default: LENGTH_UNLIMITED (DDS samples are allocated to the maximum size). |
0 or 1 |
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