Before this commit, we always synced the metadata with superuser.
However, that creates various edge cases such as visibility errors
or self distributed deadlocks or complicates user access checks.
Instead, with this commit, we use the current user to sync the metadata.
Note that, `start_metadata_sync_to_node` still requires super user
because accessing certain metadata (like pg_dist_node) always require
superuser (e.g., the current user should be a superuser).
However, metadata syncing operations regarding the distributed
tables can now be done with regular users, as long as the user
is the owner of the table. A table owner can still insert non-sense
metadata, however it'd only affect its own table. So, we cannot do
anything about that.
With this commit, we implemented some basic features of reference tables.
To start with, a reference table is
* a distributed table whithout a distribution column defined on it
* the distributed table is single sharded
* and the shard is replicated to all nodes
Reference tables follows the same code-path with a single sharded
tables. Thus, broadcast JOINs are applicable to reference tables.
But, since the table is replicated to all nodes, table fetching is
not required any more.
Reference tables support the uniqueness constraints for any column.
Reference tables can be used in INSERT INTO .. SELECT queries with
the following rules:
* If a reference table is in the SELECT part of the query, it is
safe join with another reference table and/or hash partitioned
tables.
* If a reference table is in the INSERT part of the query, all
other participating tables should be reference tables.
Reference tables follow the regular co-location structure. Since
all reference tables are single sharded and replicated to all nodes,
they are always co-located with each other.
Queries involving only reference tables always follows router planner
and executor.
Reference tables can have composite typed columns and there is no need
to create/define the necessary support functions.
All modification queries, master_* UDFs, EXPLAIN, DDLs, TRUNCATE,
sequences, transactions, COPY, schema support works on reference
tables as expected. Plus, all the pre-requisites associated with
distribution columns are dismissed.
Text datums can't be directly accessed via the struct equivalence trick
used to access catalogs. That's because, as an optimization, they're
sometimes aligned to 1 byte ("text"'s alignment), and sometimes to 4
bytes. That depends on it being a short
varlena (cf. VARATT_NOT_PAD_BYTE) or not.
In the case at hand here, partkey became longer than 127 characters -
the boundary for short varlenas (cf. VARATT_CAN_MAKE_SHORT()). Thus it
became 4 byte/int aligned. Which lead to the direct struct access
accessing the wrong data.
The fix is simply to never access partkey that way - to enforce that,
hide partkey ehind the usual ifdef.
Fixes: #674
Ahmet Gedemenli
Onder Kalaci
SaitTalhaNisanci
Onder Kalaci
Metin Doslu
Marco Slot
Burak Yucesoy
Andres Freund
Jason Petersen