This change allows seeing the names of columns of `master_add_node`,
using `SELECT * FROM master_add_node(...)` by specifying output
columns in UDF definition.
So far placements were assigned an Oid, but that was just used to track
insertion order. It also did so incompletely, as it was not preserved
across changes of the shard state. The behaviour around oid wraparound
was also not entirely as intended.
The newly introduced, explicitly assigned, IDs are preserved across
shard-state changes.
The prime goal of this change is not to improve ordering of task
assignment policies, but to make it easier to reference shards. The
newly introduced UpdateShardPlacementState() makes use of that, and so
will the in-progress connection and transaction management changes.
Related to #786
This change adds the `pg_dist_node` table that contains the information
about the workers in the cluster, replacing the previously used
`pg_worker_list.conf` file (or the one specified with `citus.worker_list_file`).
Upon update, `pg_worker_list.conf` file is read and `pg_dist_node` table is
populated with the file's content. After that, `pg_worker_list.conf` file
is renamed to `pg_worker_list.conf.obsolete`
For adding and removing nodes, the change also includes two new UDFs:
`master_add_node` and `master_remove_node`, which require superuser
permissions.
'citus.worker_list_file' guc is kept for update purposes but not used after the
update is finished.
Eren Basak
Andres Freund
Brian Cloutier