* Add default column to databases to support `show retention policies`
* add unit test for show retention policies
* update transpiler readme for show databases, show retention policies
The transpiler will normalize the `_time` column by dropping any
existing time column and then duplicating `_start` when the query is an
aggregate type.
This works for the selectors because they did not normalize their
`_time` column at all and, while the aggregates did normalize their
`_time` column, we have made the decision to remove that functionality
and have aggregates not set a `_time` column at all.
Instead of generating multiple cursors, a pivot is used to join fields
within the same series.
This should be easier than generating a new cursor for everything.
The transpiler now supports basic windowing. The window offsets are not
supported yet at all.
For windowing, we use the window function to split the points, perform
the aggregate/selector operation, and then we put them back into the
same window so they are within the same table as they originally were
located in. This is now reflected in the spec and the code.
This extra flexibility makes it easier for the transpiler to generate a
specification since the map step can be focused on only generating the
columns related to fields. In particular, it makes it easier to
implement wildcards for tags because the tags will get passed along with
the partition key.
The transpiler should use a bucket for the `from()` call instead of the
database parameter which will likely be deprecated. The bucket that it
will read data from is `db/rp` and, if the retention policy isn't
specified, `autogen` will be used as the default.
There are a few changes to how the transpiler works. The first is that
the streams are now abstracted behind a `cursor` interface. The
interface keeps track of which AST nodes (like variables or function
calls) are represented by the data inside of the stream and the method
of how to access the underlying data. This makes it easier to make a
generic interface for things like the join and map operations. This also
makes it easier to, in the future, use the same code from the map
operation for a filter so we can implement conditions.
This also follows the transpiler readme's methods and takes advantage of
the updates to the ifql language. This means it will group the relevant
cursors into a cursor group, perform any necessary joins, and allow us
to continue building on this as we flesh out more parts of the
transpiler and the language.
The cursor interface makes it so we no longer have to keep a symbol
table mapping the generated names to the locations because that is all
kept within the incoming cursor rather than as a separate data
structure.
It also splits the transpiler into more files so it is easier to find
the relevant code for each stage of the transpiler.
Update the transpiler docs to account for a change in the query
language. A slightly different method is now used with some
clarifications previously existing problems.
The readme is also indexed with a table of contents for easier reading.
The transpiler will now yield each statement using the statement id so
the result encoder can properly order the results and encode the
statement id. This behavior is now in the transpiler spec.
Jonathan A. Sternberg
Christopher M. Wolff
Adam
Nathaniel Cook
Adam Perlin
Adam