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Teja Mupparti 5ba7efbc0e Support MERGE on distributed tables with restrictions 
This implements the phase - II of MERGE sql support

Support routable query where all the tables in the merge-sql are distributed, co-located, and both the source and
target relations are joined on the distribution column with a constant qual. This should be a Citus single-task
query. Below is an example.

SELECT create_distributed_table('t1', 'id');
SELECT create_distributed_table('s1', 'id', colocate_with => ‘t1’);

MERGE INTO t1
USING s1 ON t1.id = s1.id AND t1.id = 100
WHEN MATCHED THEN
UPDATE SET val = s1.val + 10
WHEN MATCHED THEN
DELETE
WHEN NOT MATCHED THEN
INSERT (id, val, src) VALUES (s1.id, s1.val, s1.src)

Basically, MERGE checks to see if

There are a minimum of two distributed tables (source and a target).
All the distributed tables are indeed colocated.
MERGE relations are joined on the distribution column
MERGE .. USING .. ON target.dist_key = source.dist_key
The query should touch only a single shard i.e. JOIN AND with a constant qual
MERGE .. USING .. ON target.dist_key = source.dist_key AND target.dist_key = <>
If any of the conditions are not met, it raises an exception.

(cherry picked from commit 44c387b978)

This implements MERGE phase3

Support pushdown query where all the tables in the merge-sql are Citus-distributed, co-located, and both
the source and target relations are joined on the distribution column. This will generate multiple tasks
which execute independently after pushdown.

SELECT create_distributed_table('t1', 'id');
SELECT create_distributed_table('s1', 'id', colocate_with => ‘t1’);

MERGE INTO t1
USING s1
ON t1.id = s1.id
        WHEN MATCHED THEN
                UPDATE SET val = s1.val + 10
        WHEN MATCHED THEN
                DELETE
        WHEN NOT MATCHED THEN
                INSERT (id, val, src) VALUES (s1.id, s1.val, s1.src)

*The only exception for both the phases II and III is, UPDATEs and INSERTs must be done on the same shard-group
as the joined key; for example, below scenarios are NOT supported as the key-value to be inserted/updated is not
guaranteed to be on the same node as the id distribution-column.

MERGE INTO target t
USING source s ON (t.customer_id = s.customer_id)
WHEN NOT MATCHED THEN - -
     INSERT(customer_id, …) VALUES (<non-local-constant-key-value>, ……);

OR this scenario where we update the distribution column itself

MERGE INTO target t
USING source s On (t.customer_id = s.customer_id)
WHEN MATCHED THEN
     UPDATE SET customer_id = 100;

(cherry picked from commit fa7b8949a8)
 		2023-03-16 12:52:23 -07:00
..
columnar_freezing Pg15 support (#6085) 2022-08-24 17:59:17 +02:00
hammerdb rename citus hammerdb branch prefix as citus_github_push (#3925) 2020-06-18 21:11:58 +03:00
recovery Pg15 support (#6085) 2022-08-24 17:59:17 +02:00
regress Support MERGE on distributed tables with restrictions 2023-03-16 12:52:23 -07:00