Stabilize heartbeat aggregate

Changelog.md

@@ -11,6 +11,9 @@ This changelog should be updated as part of a PR if the work is worth noting (mo
 #### Bug fixes
 - [#715](https://github.com/timescale/timescaledb-toolkit/pull/715): Fix out-of-bounds indexing error in `state_agg` rollup
 
+#### Stabilized features
+- [#722](https://github.com/timescale/timescaledb-toolkit/pull/722): Stabilize heartbeat aggregate.
+
 #### Other notable changes
 - [#716](https://github.com/timescale/timescaledb-toolkit/issues/716): Add arrow operator support for counter aggregate and time-weighted aggregate interpolated accessors.
 - [#716](https://github.com/timescale/timescaledb-toolkit/issues/716): Remove experimental versions of interpolated accessors for counter aggregate and time-weighted aggregates.  The stable versions introduced in 1.14.0 should be used instead.

docs/test_caggs.md

@@ -23,7 +23,8 @@ AS SELECT
     hyperloglog(64, value1) as hll,
     counter_agg(time, value1) as counter,
     stats_agg(value1, value2) as stats,
-    timevector(time, value2) as tvec
+    timevector(time, value2) as tvec,
+    heartbeat_agg(time, time_bucket('7 day'::interval, time), '1w', '55m') as hb
 FROM test
 GROUP BY time_bucket('7 day'::interval, time);
 ```
@@ -114,3 +115,22 @@ ORDER BY week;
  2020-07-20 00:00:00+00 |   168
  2020-07-27 00:00:00+00 |    59
 ```
+
+```SQL
+SELECT week, uptime(hb), interpolated_uptime(hb, LAG(hb) OVER (ORDER BY week))
+FROM weekly_aggs
+WHERE week > '2020-06-01'
+ORDER BY week;
+```
+```output
+          week          |     uptime      | interpolated_uptime 
+------------------------+-----------------+---------------------
+ 2020-06-08 00:00:00+00 | 6 days 10:00:00 | 6 days 10:00:00
+ 2020-06-15 00:00:00+00 | 6 days 10:00:00 | 6 days 10:00:00
+ 2020-06-22 00:00:00+00 | 6 days 10:00:00 | 6 days 10:00:00
+ 2020-06-29 00:00:00+00 | 6 days 10:00:00 | 6 days 10:00:00
+ 2020-07-06 00:00:00+00 | 6 days 10:00:00 | 6 days 10:00:00
+ 2020-07-13 00:00:00+00 | 6 days 10:00:00 | 6 days 10:00:00
+ 2020-07-20 00:00:00+00 | 6 days 10:00:00 | 6 days 10:00:00
+ 2020-07-27 00:00:00+00 | 2 days 06:05:00 | 2 days 06:05:00
+```

extension/src/accessors.rs

@@ -97,8 +97,33 @@ accessor! { open_time() }
 accessor! { high_time() }
 accessor! { low_time() }
 accessor! { close_time() }
+accessor! { live_ranges() }
+accessor! { dead_ranges() }
+accessor! { uptime() }
+accessor! { downtime() }
+
 // The rest are more complex, with String or other challenges.  Leaving alone for now.
 
+pg_type! {
+    #[derive(Debug)]
+    struct AccessorLiveAt {
+        time: u64,
+    }
+}
+
+ron_inout_funcs!(AccessorLiveAt);
+
+#[pg_extern(immutable, parallel_safe, name = "live_at")]
+pub fn accessor_live_at(ts: crate::raw::TimestampTz) -> AccessorLiveAt<'static> {
+    unsafe {
+        flatten! {
+            AccessorLiveAt {
+                time: ts.0.value() as u64,
+            }
+        }
+    }
+}
+
 pg_type! {
     #[derive(Debug)]
     struct AccessorStdDev<'input> {