Also in this commit:
- Rename time/space to open/closed for more generality.
- Create a Point data type for mapping a tuple to an
N-dimensional space.
- Numerous fixes and cleanups.
This is the first stab at updating the table and data type
definitions in the catalog module in the C code. This also
adds functions for natively scanning the dimension and
dimension_slice tables.
The current schema and code support only one "time" and one "space"
dimension for partitioning. While this is probably good enough for
many applications, it won't allow partitioning along two "space"
dimensions, like longitude and latitude, for instance.
This commit is a first stab at refactoring the metadata schema and
internal functionality to support any number of partitioning
dimensions. The idea is to think of a hypertable as partitioned in N
dimensions, where a partition (chunk) is a hypercube in the
N-dimensional hyperspace. Each dimension is divided into a number of
"slices" (dimensional partitions) that each occupies a range along the
dimension's keyspace axis.
A dimension can either be "closed" or "open", indicating a space-like
or time-like dimension, respectively. Closed dimensions have a limited
number of partitions that cover the entire domain. Open dimensions have
an unlimited number of partitions and thus must be created on-demand
as needed for the inserted data.
Note that the open/closed notation is preferred over time/space, since
an open dimension could be used for something other than time (for
instance, a sequence number). Conversely, closed dimensions need not be
space-like as it is entirely possible to use time as a closed
dimension.
Another advantage of this refactoring is that it now unifies a lot
of the logic for time and space that used to be separate.
On a schema-level, this gets rid of partition/partitition_epoch tables and
replace them with dimension, dimension_slice, and chunk_constraint. It
also removes the time columns associated with a chunk and instead makes
this a separate dimension stored as a chunk_constraint.
Clean up the table schema to get rid of legacy tables and functionality
that makes it more difficult to provide an upgrade path.
Notable changes:
* Get rid of legacy tables and code
* Simplify directory structure for SQL code
* Simplify table hierarchy: remove root table and make chunk tables
* inherit directly from main table
* Change chunk table suffix from _data to _chunk
* Simplify schema usage: _timescaledb_internal for internal functions.
* _timescaledb_catalog for metadata tables.
* Remove postgres_fdw dependency
* Improve code comments in sql code
