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[23974] Better explanation for depth vs mspi behavior (backport #1194) #1197

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MiguelCompany merged 1 commit into from
Feb 4, 2026
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[23974] Better explanation for depth vs mspi behavior (backport #1194) #1197

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16 changes: 10 additions & 6 deletions docs/fastdds/dds_layer/core/policy/standardQosPolicies.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -482,6 +482,9 @@ The HistoryQos must be set consistently with the :ref:`resourcelimitsqospolicy`,
|ResourceLimitsQosPolicy::max_samples_per_instance-api|.
Also, |ResourceLimitsQosPolicy::max_samples-api| must be equal or higher than the product of
|ResourceLimitsQosPolicy::max_samples_per_instance-api| times |ResourceLimitsQosPolicy::max_instances-api|.
* When |HistoryQosPolicy::depth-api| is set higher than
|ResourceLimitsQosPolicy::max_samples_per_instance-api|, the effective depth used
will be limited by |ResourceLimitsQosPolicy::max_samples_per_instance-api|.
* The |HistoryQosPolicy::depth-api| cannot be lower or equal than zero.
If an unlimited depth is required, please consider using |HistoryQosPolicy::kind-api| as |KEEP_ALL_HISTORY_QOS-api|.
* Setting the |HistoryQosPolicy::kind-api| as |KEEP_ALL_HISTORY_QOS-api| entails that limits are set by the
Expand Down Expand Up @@ -1214,19 +1217,19 @@ List of QoS Policy data members:
+----------------------------------------------------------------------------------------+-------------+---------------+

* |ResourceLimitsQosPolicy::max_samples-api|: Controls the maximum number of samples that the DataWriter or DataReader
can manage across all the
instances associated with it.
can manage across all the instances associated with it.
In other words, it represents the maximum samples that the middleware can store for a DataReader or DataWriter.
**Value less or equal to 0 means infinite resources.**
* |ResourceLimitsQosPolicy::max_instances-api|: Controls the maximum number of instances that a DataWriter or
DataReader can manage.
**Value less or equal to 0 means infinite resources.**
* |ResourceLimitsQosPolicy::max_samples_per_instance-api|: Controls the maximum number of samples within an instance
that the DataWriter or
DataReader can manage.
that the DataWriter or DataReader can manage.
It will be ignored for topics without keys (|ResourceLimitsQosPolicy::max_samples-api| will be used instead).
**Value less or equal to 0 means infinite resources.**
* |ResourceLimitsQosPolicy::allocated_samples-api|: States the number of samples that will be allocated on
initialization.
Will be limited by |ResourceLimitsQosPolicy::max_samples-api| (i.e. the minimum between both values will be used).
* |ResourceLimitsQosPolicy::extra_samples-api|: States the number of extra samples that will be allocated on
the pool, so the maximum number of samples on the pool will be
|ResourceLimitsQosPolicy::max_samples-api| plus |ResourceLimitsQosPolicy::extra_samples-api|.
Expand All @@ -1248,8 +1251,9 @@ conditions:
* The value of |ResourceLimitsQosPolicy::max_samples-api| must be higher or equal to the value of
|ResourceLimitsQosPolicy::max_samples_per_instance-api|.
* The value established for the :ref:`historyqospolicy` |HistoryQosPolicy::depth-api| must be lower or equal to the
value stated for
|ResourceLimitsQosPolicy::max_samples_per_instance-api|.
value stated for |ResourceLimitsQosPolicy::max_samples_per_instance-api|.
If the depth is configured higher, |ResourceLimitsQosPolicy::max_samples_per_instance-api|
will take precedence as the effective depth.


Example
Expand Down