Whenever periodic stats are streamed, the collector reads the stats from its internal cache, instead of fetching the stats from the hardware. When the data is read from the sensor paths of Stats manager cache, the rate calculation shows spikes. This behavior is due to the timestamp from the collector that is off by several seconds. Therefore, timestamp of some other collector takes precedence because timestamps of collectors are not in synchronization with the current timestamp. This is observed when there are multiple collectors providing stats updates for the same interface.

The YANG data model for Stats manager Cisco-IOS-XR-infra-statsd-oper.yang is enhanced to enable the collector to read periodic stats data from the router using hardware timestamp.

The hardware timestamp is taken into account when a primary collector (for generic or proto stats) provides stats updates from the hardware to the Stats manager. With hardware timestamping in rate computation while streaming periodic stats, the spikes due to the timestamp issue is resolved.

The hardware timestamp is updated only when the collector attempts to read the counters from hardware. Else, the value remains 0. The latest stats can be streamed at a minimum cadence of 10 seconds and periodic stats at a cadence of 30 seconds. The support is available only for physical interfaces and subinterfaces, and bundle interface and subinterfaces.

When there is no traffic flow on protocols for an interface, the hardware timestamp for the protocols is published as 0. This is due to non-synchronized timestamps sent by the collector for protocols in traffic as compared to non-traffic scenarios.

A non-zero value is published for protocols that have stats published by a primary collector for both traffic and non-traffic scenarios.

Note	The hardware timestamp is supported only for primary collectors. When the hardware has no update, the timestamp will be same. However generic counters are computed for primary and non-primary collectors. The non-primary collectors show the latest stats, but not the timestamp.

When the counters are cleared for an interface using clear counters interface command, all counter-related data including the timestamps for the interface is cleared. After all counter values are cleared and set to 0, the last data time is updated only when there is a request for it from a collector. For example, last data time gets updated from a collector:

Router#:Aug  7 09:01:08.471 UTC: statsd_manager_l[168]: Updated last data time for ifhandle 0x02000408, 
stats type 2 from collector with node 0x100, JID 250, last data time 1596790868. 
INPUT: last 4294967295 updated 1596469986. OUTPUT: last 4294967295 updated 1596469986

{"node_id_str":"MGBL_MTB_5504","subscription_id_str":"app_TEST_200000001",
"encoding_path":"Cisco-IOS-XR-infra-statsd-oper:infra-statistics/interfaces/interface/cache/generic-counters",
"collection_id":"7848",
"collection_start_time":"1596790879567",
"msg_timestamp":"1596790879571","data_json":
[{"timestamp":"1596790879570","keys":[{"interface-name":"FortyGigE0/1/0/11"}],
"content":{"packets-received":"0","bytes-received":"0","packets-sent":"0",
"bytes-sent":"0","multicast-packets-received":"0","broadcast-packets-received":"0",
"multicast-packets-sent":"0","broadcast-packets-sent":"0","output-drops":0,"output-queue-drops":0,
"input-drops":0,"input-queue-drops":0,"runt-packets-received":0,"giant-packets-received":0,
"throttled-packets-received":0,"parity-packets-received":0,"unknown-protocol-packets-received":0,
"input-errors":0,"crc-errors":0,"input-overruns":0,"framing-errors-received":0,"input-ignored-packets":0,
"input-aborts":0,"output-errors":0,"output-underruns":0,"output-buffer-failures":0,"output-buffers-swapped-out":0,
"applique":0,"resets":0,"carrier-transitions":0,"availability-flag":0,
"last-data-time":"1596790868","hardware-timestamp":"0",
"seconds-since-last-clear-counters":15,"last-discontinuity-time":1596469946,"seconds-since-packet-received":0,
"seconds-since-packet-sent":0}}],"collection_end_time":"1596790879571"}