==== History QoS ====
Is a [[ddsf:public:guidebook:06_append:glossary:q:quality_of_service_qos_policies|QoS policy]] that specifies the number of samples kept by the [[ddsf:public:guidebook:06_append:glossary:m:midware|middleware]] engine.  
[[ddsf:public:guidebook:06_append:glossary:d:data_distribution_service_dds]] will only attempt to keep the most recent ‘depth’ of samples 
(KEEP_LAST) or ALL samples (KEEP_ALL) of each [[ddsf:public:guidebook:06_append:glossary:i:instance|instance]] of data 
identified by its [ddsf:private:cookbook:06_append:glossary:k:key|key]].

Source: [[https://istkb.adlinktech.com/article/vortex-opensplice-dds-glossary/ | OpenSplice Glossary]]