* Add support for dist insert select by selecting from a reference
table.
This was the only pushable insert .. select case that
#6773 didn't cover.
* For the cases where we insert into a Citus table but the INSERT ..
SELECT
query cannot be pushed down, allow pull-to-coordinator when possible.
Remove the checks that we had at the very beginning of
CreateInsertSelectPlanInternal so that we can try insert .. select via
pull-to-coordinator for the cases where we cannot push-down the insert
.. select query. What we support via pull-to-coordinator is still
limited due to lacking of logical planner support for SELECT queries,
but this commit at least allows using pull-to-coordinator for the cases
where the select query can be planned via router planner, without
limiting ourselves to restrictive top-level checks.
Also introduce some additional restrictions into
CreateDistributedInsertSelectPlan for the cases it was missing to check
for null-shard-key tables. Indeed, it would make more sense to have
those checks for distributed tables in general, via separate PRs against
main branch. See https://github.com/citusdata/citus/pull/6817.
* Add support for inserting into a Postgres table.
Enable router planner and a limited version of INSERT .. SELECT planner
for the queries that reference colocated null shard key tables.
* SELECT / UPDATE / DELETE / MERGE is supported as long as it's a router
query.
* INSERT .. SELECT is supported as long as it only references colocated
null shard key tables.
Note that this is not only limited to distributed INSERT .. SELECT but
also
covers a limited set of query types that require pull-to-coordinator,
e.g.,
due to LIMIT clause, generate_series() etc. ...
(Ideally distributed INSERT .. SELECT could handle such queries too,
e.g.,
when we're only referencing tables that don't have a shard key, but
today
this is not the case. See
https://github.com/citusdata/citus/pull/6773#discussion_r1140130562.
Onur Tirtir