>
> - Cron syntax allows you to construct only absolute lookbacks (i.e.
> "every tuesday at 3PM" not "every tuesday at the current hour")
I think Cron would work for this. I am no expert on cron expressions, but
I think the following examples would work.
- If you want "every Tuesday at 3 PM"
- 0 0 15 ? * TUE *
- If you want "every Tuesday at current hour" then use something like
the "?" placeholder maybe.
- 0 0 ? ? * TUE *
- Cron syntax allows you to specify a point in time, not a duration. We
> could, of course, specify a duration as another argument
Yes, a separate argument would be necessary. We would have to allow the
user to specify either a "start from date/time" or the "number of intervals
to look back".
Cron syntax does not allow you to skip things like holidays, etc.
I agree, out-of-the-box Cron does not solve holiday calendars. But this
would be a smaller problem to solve then creating our own DSL.
There is a tradition of creating shortcuts that look something like @Daily
or @Weekdays or @Tuesdays that we could also use to make things easier for
users.
I have used Quartz with cron expressions in the past and there was some way
to handle holidays with that. I think you could create a custom calendar
for the holidays and call it something; aka @USHolidays. And then you
would say "every Tuesday" except @USHolidays or something like that. I'd
have to look into this some more.
And there are also nice online Cron expression "translators" that we could
mimic in a Metron user interface. For example, https://crontab.guru.
On Tue, Jan 31, 2017 at 12:00 PM, Casey Stella <ceste...@gmail.com> wrote:
> I actually did consider cron initially but dismissed it for the following
> reasons:
>
> - Cron syntax allows you to construct only absolute lookbacks (i.e.
> "every tuesday at 3PM" not "every tuesday at the current hour")
> - Cron syntax allows you to specify a point in time, not a duration. We
> could, of course, specify a duration as another argument
> - Cron syntax does not allow you to skip things like holidays, etc.
>
> You could use Cron syntax as part of a broader API to specify the days to
> look back and have other arguments handle the aspects that cron doesn't
> support out of the box. I share your concern at making another DSL, but
> cron seemed to not be a complete solution and it's syntax, despite being
> well known by admins, may not be well known to analysts. Also, and this is
> just a personal bias, I find it inscrutable without a fair amount of
> wikipedia and man page reading.
>
> On Tue, Jan 31, 2017 at 11:47 AM, Nick Allen <n...@nickallen.org> wrote:
>
> > I do prefer the flexibility of the DSL, but would prefer not to create
> yet
> > another DSL for our users to learn. Couldn't we somehow use cron
> > expressions for this functionality?
> >
> > On Mon, Jan 23, 2017 at 3:01 PM, Casey Stella <ceste...@gmail.com>
> wrote:
> >
> > > Hi All,
> > >
> > > I'm planning to expand the capabilities of PROFILE_GET and wanted to
> pass
> > > an idea past the community.
> > >
> > > *Current State*
> > >
> > > Currently, the functionality of PROFILE_GET is fairly straightforward:
> > >
> > > - profile - The name of the profile.
> > > - entity - The name of the entity.
> > > - durationAgo - How long ago should values be retrieved from?
> > > - units - The units of 'durationAgo'.
> > > - groups_list - Optional, must correspond to the 'groupBy' list used
> > in
> > > profile creation - List (in square brackets) of groupBy values used
> to
> > > filter the profile. Default is the empty list, meaning groupBy was
> not
> > > used
> > > when creating the profile.
> > > - config_overrides - Optional - Map (in curly braces) of name:value
> > > pairs, each overriding the global config parameter of the same name.
> > > Default is the empty Map, meaning no overrides.
> > >
> > > This has the advantage of providing a relatively simple mechanism to
> > > support the dominant use-case, gathering the profiles for a trailing
> > > window. The issues, however, are a couple:
> > >
> > > - We may need more complex semantics for specifying the window
> > > (motivated below)
> > > - As such, this couples the gathering of the profiles with the
> > > specification of the window.
> > >
> > > I propose to decouple these two concepts. I propose that we extract the
> > > notion of the lookback into a separate, more featureful function called
> > > PROFILE_LOOKBACK() which could be composed with an adjusted
> PROFILE_GET,
> > > whose arguments look like:
> > >
> > >
> > > - profile - The name of the profile.
> > > - entity - The name of the entity.
> > > - timestamps - The list of timestamps to retrieve
> > > - groups_list - Optional, must correspond to the 'groupBy' list used
> > in
> > > profile creation - List (in square brackets) of groupBy values used
> to
> > > filter the profile. Default is the empty list, meaning groupBy was
> not
> > > used
> > > when creating the profile.
> > > - config_overrides - Optional - Map (in curly braces) of name:value
> > > pairs, each overriding the global config parameter of the same name.
> > > Default is the empty Map, meaning no overrides.
> > >
> > > So, PROFILE_GET would have the output of PROFILE_LOOKBACK passed to it
> as
> > > its 3rd argument (e.g. PROFILE_GET( 'my_profile', 'my_entity',
> > > PROFILE_LOOKBACK(...)) ).
> > >
> > > *Motivation for Change*
> > >
> > > The justification for this is that sometimes you want to compare time
> > bins
> > > for a long duration back, but you don't want to skew the data by
> > including
> > > periods that aren't distributionally similar (due to seasonal data, for
> > > instance). You might want to compare a value to statistically baseline
> > of
> > > the median of the values for the same time window on the same day for
> the
> > > last month (e.g. every tuesday at this time).
> > >
> > > Also, we might want a trailing window that does not start at the
> current
> > > time (in wall-clock), but rather starts an hour back or from the time
> > that
> > > the data was originally ingested.
> > >
> > >
> > > *PROFILE_LOOKBACK*
> > >
> > > I propose that we support the following features:
> > >
> > > - A starting point that is not current time
> > > - Sparse bins (i.e. the last hour for every tuesday for the last
> > month)
> > > - The ability to skip events (e.g. weekends, holidays)
> > >
> > >
> > > This would result in a new function with the following arguments:
> > >
> > > -
> > >
> > > from - The lookback starting point (default to now)
> > > -
> > >
> > > fromUnits - The units for the lookback starting point
> > > -
> > >
> > > to - The ending point for the lookback window (default to from +
> > > binSize)
> > > -
> > >
> > > toUnits - The units for the lookback ending point
> > > -
> > >
> > > including - A list of conditions which we would skip.
> > > - weekend
> > > - holiday
> > > - sunday through saturday
> > > -
> > >
> > > excluding - A list of conditions which we would skip.
> > > - weekend
> > > - holiday
> > > - sunday through saturday
> > > -
> > >
> > > binSize - The size of the lookback bin
> > > -
> > >
> > > binUnits - The units of the lookback bin
> > >
> > > Given the number of arguments and their complexity and the fact that
> > many,
> > > many are optional, I propose that either
> > >
> > > - PROFILE_LOOKBACK take a Map so that we can get essentially named
> > > params in stellar.
> > > - PROFILE_LOOKBACK accept a string backed by a DSL to express these
> > > criteria
> > >
> > >
> > > Ok, so that's a lot to take in. How about we look at some motivating
> > > use-cases.
> > >
> > > *Base Case: A lookback of 1 hour ago*
> > >
> > > As a map, this would look like:
> > >
> > > PROFILE_LOOKBACK( { 'binSize' : 1, 'binUnits' : 'HOURS' } )
> > >
> > > As a DSL this would look like:
> > > PROFILE_LOOKBACK( '1 hour bins from now')
> > >
> > >
> > > *The same time window every tuesday for the last month starting one
> hour
> > > ago*
> > >
> > > Just to make this as clear as possible, if this is run at 3PM on Monday
> > > January 23rd, 2017, it would include the following bins:
> > >
> > > - January 17th, 2PM - 3PM
> > > - January 10th, 2PM - 3PM
> > > - January 3rd, 2PM - 3PM
> > > - December 27th, 2PM - 3PM
> > >
> > > As a map, this would look like:
> > >
> > > PROFILE_LOOKBACK( { 'from' : 1, 'fromUnits' : 'HOURS', 'to' : 1,
> > 'toUnits'
> > > : 'MONTH', 'including' : [ 'tuesday' ], 'binSize' : 1, 'binUnits' :
> > 'HOURS'
> > > } )
> > >
> > > As a DSL this would look like:
> > > PROFILE_LOOKBACK( '1 hour bins from 1 hour to 1 month including
> > tuesdays')
> > >
> > > *The same time window every sunday for the last month starting one hour
> > ago
> > > skipping holidays*
> > >
> > > Just to make this as clear as possible, if this is run at 3PM on Monday
> > > January 22rd, 2017, it would include the following bins:
> > >
> > > - January 16th, 2PM - 3PM
> > > - January 9th, 2PM - 3PM
> > > - January 2rd, 2PM - 3PM
> > > - NOT December 25th
> > >
> > > As a map, this would look like:
> > >
> > > PROFILE_LOOKBACK( { 'from' : 1, 'fromUnits' : 'HOURS', 'to' : 1,
> > 'toUnits'
> > > : 'MONTH', 'including' : [ 'tuesday'], 'excluding' : [ 'holidays' ],
> > > 'binSize' : 1, 'binUnits' : 'HOURS' } )
> > >
> > > As a DSL this would look like:
> > > PROFILE_LOOKBACK( '1 hour bins from 1 hour to 1 month including
> tuesdays
> > > excluding holidays')
> > >
> > > *DSL vs API*
> > >
> > > So, here's my personal rundown of the two approaches:
> > >
> > > DSL:
> > >
> > > - PRO
> > > - Clear. As you can see, it reads like a sentence
> > > - Concise
> > > - CON:
> > > - More complex to implement
> > > - Another DSL to learn
> > >
> > > API:
> > >
> > > - PRO
> > > - Simpler to implement (though marginally so, IMO)
> > > - CON
> > > - A bit more complex to understand (also, IMO)
> > >
> > > I'd like to solicit feedback from the community at this point:
> > >
> > > - What do you think of this change?
> > > - Would you prefer the DSL, API or other approach?
> > >
> > > Thanks,
> > >
> > > Casey
> > >
> >
> >
> >
> > --
> > Nick Allen <n...@nickallen.org>
> >
>
--
Nick Allen <n...@nickallen.org>
