Deadlock when specifying constraint name for a parent table with a partition with a long name

[naisila]

Steps to reproduce:

-- create partitioned table
CREATE TABLE distributed_partitioned_table (
    id serial NOT NULL,
    partition_col int NOT NULL,
    PRIMARY KEY (id, partition_col)
) PARTITION BY RANGE (partition_col);

-- add normal length name partition
CREATE TABLE distributed_partitioned_table_p1 PARTITION OF distributed_partitioned_table 
FOR VALUES FROM (1) TO (100);

-- add long name partition
CREATE TABLE distributed_partitioned_table_p2_longlonglonglonglonglonglong_name PARTITION OF distributed_partitioned_table 
FOR VALUES FROM (100) TO (200);

-- distribute
SELECT create_distributed_table('distributed_partitioned_table', 'id');

-- Add a unique constraint with a name to the distributed partitioned table
-- this seems to deadlock sometimes for the long name partition
SET client_min_messages TO DEBUG1;
ALTER TABLE distributed_partitioned_table ADD CONSTRAINT dist_unique_named UNIQUE(id, partition_col);

ERROR:  canceling the transaction since it was involved in a distributed deadlock

[naisila]

We are only calling PrepareAlterTableStmtForConstraint in cases where we don't have a constraint name specified in the DDL.