Pushing down the CALLs to the node that the CALL is executed is
dangerous and could lead to infinite recursion.
When the coordinator added as worker, Citus was by chance preventing
this. The coordinator was marked as "not metadatasynced" node
in pg_dist_node, which prevented CALL/function delegation to happen.
With this commit, we do the following:
- Fix metadatasynced column for the coordinator on pg_dist_node
- Prevent pushdown of function/procedure to the same node that
the function/procedure is being executed. Today, we do not sync
pg_dist_object (e.g., distributed functions metadata) to the
worker nodes. But, even if we do it now, the function call delegation
would prevent the infinite recursion.
* Not allow removing a single node with ref tables
We should not allow removing a node if it is the only node in the
cluster and there is a data on it. We have this check for distributed
tables but we didn't have it for reference tables.
* Update src/test/regress/expected/single_node.out
Co-authored-by: Onur Tirtir <onurcantirtir@gmail.com>
* Update src/test/regress/sql/single_node.sql
Co-authored-by: Onur Tirtir <onurcantirtir@gmail.com>
The reason we should use ActiveReadableNodeList instead of ActiveReadableNonCoordinatorNodeList is that if coordinator is added to cluster as a worker, it should be counted as well. Otherwise if there is only coordinator in the cluster, the count will be 0, hence we get a warning.
In MultiTaskTrackerExecute, we should connect to coordinator if it is
added to the cluster because it will also be assigned tasks.
ActiveReadableWorkerNodeList doesn't include coordinator, however if
coordinator is added as a worker, we should also include that while
planning. The current methods are very easily misusable and this
requires a refactoring to make the distinction between methods that
include coordinator and that don't very explicit as they can introduce
subtle/major bugs pretty easily.
Static analysis found an issue where we could dereference `NULL`, because
`CreateDummyPlacement` could return `NULL` when there were no workers. This
PR changes it so that it never returns `NULL`, which was intended by
@marcocitus when doing this change: https://github.com/citusdata/citus/pull/3887/files#r438136433
While adding tests for citus on a single node I also added some more basic
tests and it turns out we error out on repartition joins. This has been
present since `shouldhaveshards` was introduced and is not trivial to fix.
So I created a separate issue for this: https://github.com/citusdata/citus/issues/3996
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