Previously if you issued a CQ with a resample interval higher than the
query interval, such as the following:
CREATE CONTINUOUS QUERY cq ON db
RESAMPLE EVERY 4m
BEGIN
SELECT mean(value) INTO cpu_mean FROM cpu GROUP BY time(2m)
END
This would result in strange behavior because the FOR value defaulted to
the GROUP BY interval and the minimum time passing before a CQ ran was
also the resample interval, so it wouldn't run the appropriate intervals
even if you set the resample duration to a higher value.
This tweaks the CQ runner to set the minimum interval before a bucket
becomes capable of running to the lower of the query interval or the
resample interval instead of always using the resample interval.
It also sets the default resample duration to be the higher value of the
query interval or the resample interval so the above query gets a
default of 4m instead of 2m and will execute 2 queries every 4 minutes.
If you manually set the resample duration to a lower value than the
resample interval, the old behavior will still happen and should be
considered an error.
This also makes trying to create a continuous query with a resample
duration of below the resample interval or query interval (whichever is
higher) as an error returned by the parser.
Fixes#5286.
This makes the following syntax possible:
CREATE CONTINUOUS QUERY mycq ON mydb
RESAMPLE EVERY 1m FOR 1h
BEGIN
SELECT mean(value) INTO cpu_mean FROM cpu GROUP BY time(5m)
END
The RESAMPLE option customizes how often an interval will be sampled and
the duration. The interval is customized with EVERY. Any intervals
within the resampling duration on a multiple of the resample interval
will be updated with the new results from the query.
The duration is customized with FOR. This determines how long an
interval will participate in resampling.
Both options are optional. If RESAMPLE is in the syntax, at least one of
the two needs to be given. The default for both is the interval of the
continuous query.
The service also improves tracking of the last run time and the logic of
when a query for an interval should be run. When determining the oldest
interval to run for a query, the continuous query service determines
what would have been the optimal time to perform the next query based on
the last run time. It then uses this time to determine the oldest
interval that should be run using the resample duration and will
resample all intervals between this time and the current time as opposed
to potentially forgetting about the last run in an interval if the
continuous query service gets delayed for some reason.
This removes the previous config options for customizing continuous
queries since they are no longer relevant and adds a new option of
customizing the run interval. The run interval determines how often the
continuous query service polls for when it should execute a query. This
option defaults to 1s, but can be set to 1m if the least common factor
of all continuous queries' intervals is a higher value (like 1m).
Jason Wilder
David Norton
Jonathan A. Sternberg
Cory LaNou
Edd Robinson
Daniel Morsing