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PG16 compatibility - varnullingrels additions (#7107) 

PG16 compatibility - part 7

Check out part 1 42d956888d
part 2 0d503dd5ac
part 3 907d72e60d
part 4 7c6b4ce103
part 5 6056cb2c29
part 6 b36c431abb
part 7 ee3153fe50

This commit is in the series of PG16 compatibility commits. PG16 introduced a new entry
varnnullingrels to Var, which represents our partkey in pg_dist_partition.
This commit does the necessary changes in Citus to support this.
Relevant PG commit:
2489d76c49
2489d76c4906f4461a364ca8ad7e0751ead8aa0d

More PG16 compatibility commits are coming soon ...
pull/7122/head
Naisila Puka 2023-08-15 13:07:55 +03:00 committed by GitHub
parent ee3153fe50
commit 2c50b5f7ff
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
20 changed files with 100 additions and 19 deletions
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9
src/backend/distributed/sql/udfs/citus_finish_pg_upgrade/12.1-1.sql generated
View File

@ -106,6 +106,15 @@ BEGIN
-- restore citus catalog tables
--
INSERT INTO pg_catalog.pg_dist_partition SELECT * FROM public.pg_dist_partition;
-- if we are upgrading from PG14/PG15 to PG16+,
-- we need to regenerate the partkeys because they will include varnullingrels as well.
UPDATE pg_catalog.pg_dist_partition
SET partkey = column_name_to_column(pg_dist_partkeys_pre_16_upgrade.logicalrelid, col_name)
FROM public.pg_dist_partkeys_pre_16_upgrade
WHERE pg_dist_partkeys_pre_16_upgrade.logicalrelid = pg_dist_partition.logicalrelid;
DROP TABLE public.pg_dist_partkeys_pre_16_upgrade;
INSERT INTO pg_catalog.pg_dist_shard SELECT * FROM public.pg_dist_shard;
INSERT INTO pg_catalog.pg_dist_placement SELECT * FROM public.pg_dist_placement;
INSERT INTO pg_catalog.pg_dist_node_metadata SELECT * FROM public.pg_dist_node_metadata;

9
src/backend/distributed/sql/udfs/citus_finish_pg_upgrade/latest.sql
View File

@ -106,6 +106,15 @@ BEGIN
-- restore citus catalog tables
--
INSERT INTO pg_catalog.pg_dist_partition SELECT * FROM public.pg_dist_partition;
-- if we are upgrading from PG14/PG15 to PG16+,
-- we need to regenerate the partkeys because they will include varnullingrels as well.
UPDATE pg_catalog.pg_dist_partition
SET partkey = column_name_to_column(pg_dist_partkeys_pre_16_upgrade.logicalrelid, col_name)
FROM public.pg_dist_partkeys_pre_16_upgrade
WHERE pg_dist_partkeys_pre_16_upgrade.logicalrelid = pg_dist_partition.logicalrelid;
DROP TABLE public.pg_dist_partkeys_pre_16_upgrade;
INSERT INTO pg_catalog.pg_dist_shard SELECT * FROM public.pg_dist_shard;
INSERT INTO pg_catalog.pg_dist_placement SELECT * FROM public.pg_dist_placement;
INSERT INTO pg_catalog.pg_dist_node_metadata SELECT * FROM public.pg_dist_node_metadata;

7
src/backend/distributed/sql/udfs/citus_prepare_pg_upgrade/12.1-1.sql generated
View File

@ -84,6 +84,13 @@ BEGIN
objects.colocationid
FROM pg_catalog.pg_dist_object objects,
pg_catalog.pg_identify_object_as_address(objects.classid, objects.objid, objects.objsubid) address;
-- if we are upgrading from PG14/PG15 to PG16+,
-- we will need to regenerate the partkeys because they will include varnullingrels as well.
-- so we save the partkeys as column names here
CREATE TABLE IF NOT EXISTS public.pg_dist_partkeys_pre_16_upgrade AS
SELECT logicalrelid, column_to_column_name(logicalrelid, partkey) as col_name
FROM pg_catalog.pg_dist_partition WHERE partkey IS NOT NULL AND partkey NOT ILIKE '%varnullingrels%';
END;
$cppu$;

7
src/backend/distributed/sql/udfs/citus_prepare_pg_upgrade/latest.sql
View File

@ -84,6 +84,13 @@ BEGIN
objects.colocationid
FROM pg_catalog.pg_dist_object objects,
pg_catalog.pg_identify_object_as_address(objects.classid, objects.objid, objects.objsubid) address;
-- if we are upgrading from PG14/PG15 to PG16+,
-- we will need to regenerate the partkeys because they will include varnullingrels as well.
-- so we save the partkeys as column names here
CREATE TABLE IF NOT EXISTS public.pg_dist_partkeys_pre_16_upgrade AS
SELECT logicalrelid, column_to_column_name(logicalrelid, partkey) as col_name
FROM pg_catalog.pg_dist_partition WHERE partkey IS NOT NULL AND partkey NOT ILIKE '%varnullingrels%';
END;
$cppu$;

1
src/test/regress/bin/normalize.sed
View File

@ -302,5 +302,6 @@ s/(NOTICE: issuing CREATE EXTENSION IF NOT EXISTS citus_columnar WITH SCHEMA p
s/, password_required=false//g
s/provide the file or change sslmode/provide the file, use the system's trusted roots with sslrootcert=system, or change sslmode/g
s/(:varcollid [0-9]+) :varlevelsup 0/\1 :varnullingrels (b) :varlevelsup 0/g
#endif /* PG_VERSION_NUM < PG_VERSION_16 */

2
src/test/regress/expected/citus_local_tables.out
View File

@ -635,7 +635,7 @@ FROM pg_dist_partition WHERE logicalrelid = 'citus_local_table_4'::regclass;
SELECT column_name_to_column('citus_local_table_4', 'a');
column_name_to_column
---------------------------------------------------------------------
{VAR :varno 1 :varattno 1 :vartype 23 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1}
{VAR :varno 1 :varattno 1 :vartype 23 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1}
(1 row)
SELECT master_update_shard_statistics(shardid)

4
src/test/regress/expected/citus_local_tables_mx.out
View File

@ -769,8 +769,8 @@ SELECT logicalrelid, partmethod, partkey FROM pg_dist_partition
ORDER BY logicalrelid;
logicalrelid | partmethod | partkey
---------------------------------------------------------------------
parent_dropped_col | h | {VAR :varno 1 :varattno 1 :vartype 1082 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1}
parent_dropped_col_2 | h | {VAR :varno 1 :varattno 5 :vartype 23 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 5 :location -1}
parent_dropped_col | h | {VAR :varno 1 :varattno 1 :vartype 1082 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1}
parent_dropped_col_2 | h | {VAR :varno 1 :varattno 5 :vartype 23 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 5 :location -1}
(2 rows)
-- some tests for view propagation on citus local tables

11
src/test/regress/expected/metadata_sync_helpers.out
View File

@ -1284,8 +1284,17 @@ BEGIN TRANSACTION ISOLATION LEVEL READ COMMITTED;
SET application_name to 'citus_internal gpid=10000000001';
-- with an ugly trick, update the vartype of table from int to bigint
-- so that making two tables colocated fails
UPDATE pg_dist_partition SET partkey = '{VAR :varno 1 :varattno 1 :vartype 20 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnoold 1 :varoattno 1 :location -1}'
-- include varnullingrels for PG16
SHOW server_version \gset
SELECT substring(:'server_version', '\d+')::int >= 16 AS server_version_ge_16
\gset
\if :server_version_ge_16
UPDATE pg_dist_partition SET partkey = '{VAR :varno 1 :varattno 1 :vartype 20 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 1 :varnoold 1 :varoattno 1 :location -1}'
WHERE logicalrelid = 'test_2'::regclass;
\else
UPDATE pg_dist_partition SET partkey = '{VAR :varno 1 :varattno 1 :vartype 20 :vartypmod -1 :varcollid 0 :varlevelsup 1 :varnoold 1 :varoattno 1 :location -1}'
WHERE logicalrelid = 'test_2'::regclass;
\endif
SELECT citus_internal_update_relation_colocation('test_2'::regclass, 251);
ERROR: cannot colocate tables test_2 and test_3
ROLLBACK;

2
src/test/regress/expected/multi_extension.out
View File

@ -986,7 +986,7 @@ DELETE FROM pg_dist_shard WHERE shardid = 1;
CREATE TABLE e_transactions(order_id varchar(255) NULL, transaction_id int) PARTITION BY LIST(transaction_id);
CREATE TABLE orders_2020_07_01
PARTITION OF e_transactions FOR VALUES IN (1,2,3);
INSERT INTO pg_dist_partition VALUES ('e_transactions'::regclass,'h', '{VAR :varno 1 :varattno 1 :vartype 1043 :vartypmod 259 :varcollid 100 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1}', 7, 's');
INSERT INTO pg_dist_partition VALUES ('e_transactions'::regclass,'h', '{VAR :varno 1 :varattno 1 :vartype 1043 :vartypmod 259 :varcollid 100 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1}', 7, 's');
SELECT
(metadata->>'partitioned_citus_table_exists_pre_11')::boolean as partitioned_citus_table_exists_pre_11,
(metadata->>'partitioned_citus_table_exists_pre_11') IS NULL as is_null

4
src/test/regress/expected/multi_metadata_sync.out
View File

@ -533,7 +533,7 @@ SELECT * FROM pg_dist_node ORDER BY nodeid;
SELECT * FROM pg_dist_partition WHERE logicalrelid::text LIKE 'mx_testing_schema%' ORDER BY logicalrelid::text;
logicalrelid | partmethod | partkey | colocationid | repmodel | autoconverted
---------------------------------------------------------------------
mx_testing_schema.mx_test_table | h | {VAR :varno 1 :varattno 1 :vartype 23 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 2 | s | f
mx_testing_schema.mx_test_table | h | {VAR :varno 1 :varattno 1 :vartype 23 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 2 | s | f
(1 row)
SELECT * FROM pg_dist_shard WHERE logicalrelid::text LIKE 'mx_testing_schema%' ORDER BY shardid;
@ -672,7 +672,7 @@ SELECT * FROM pg_dist_node ORDER BY nodeid;
SELECT * FROM pg_dist_partition WHERE logicalrelid::text LIKE 'mx_testing_schema%' ORDER BY logicalrelid::text;
logicalrelid | partmethod | partkey | colocationid | repmodel | autoconverted
---------------------------------------------------------------------
mx_testing_schema.mx_test_table | h | {VAR :varno 1 :varattno 1 :vartype 23 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 2 | s | f
mx_testing_schema.mx_test_table | h | {VAR :varno 1 :varattno 1 :vartype 23 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 2 | s | f
(1 row)
SELECT * FROM pg_dist_shard WHERE logicalrelid::text LIKE 'mx_testing_schema%' ORDER BY shardid;

4
src/test/regress/expected/multi_metadata_sync_0.out
View File

@ -533,7 +533,7 @@ SELECT * FROM pg_dist_node ORDER BY nodeid;
SELECT * FROM pg_dist_partition WHERE logicalrelid::text LIKE 'mx_testing_schema%' ORDER BY logicalrelid::text;
logicalrelid | partmethod | partkey | colocationid | repmodel | autoconverted
---------------------------------------------------------------------
mx_testing_schema.mx_test_table | h | {VAR :varno 1 :varattno 1 :vartype 23 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 2 | s | f
mx_testing_schema.mx_test_table | h | {VAR :varno 1 :varattno 1 :vartype 23 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 2 | s | f
(1 row)
SELECT * FROM pg_dist_shard WHERE logicalrelid::text LIKE 'mx_testing_schema%' ORDER BY shardid;
@ -672,7 +672,7 @@ SELECT * FROM pg_dist_node ORDER BY nodeid;
SELECT * FROM pg_dist_partition WHERE logicalrelid::text LIKE 'mx_testing_schema%' ORDER BY logicalrelid::text;
logicalrelid | partmethod | partkey | colocationid | repmodel | autoconverted
---------------------------------------------------------------------
mx_testing_schema.mx_test_table | h | {VAR :varno 1 :varattno 1 :vartype 23 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 2 | s | f
mx_testing_schema.mx_test_table | h | {VAR :varno 1 :varattno 1 :vartype 23 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 2 | s | f
(1 row)
SELECT * FROM pg_dist_shard WHERE logicalrelid::text LIKE 'mx_testing_schema%' ORDER BY shardid;

2
src/test/regress/expected/multi_prune_shard_list.out
View File

@ -86,7 +86,7 @@ SELECT prune_using_both_values('pruning', 'tomato', 'rose');
SELECT debug_equality_expression('pruning');
debug_equality_expression
---------------------------------------------------------------------
{OPEXPR :opno 98 :opfuncid 67 :opresulttype 16 :opretset false :opcollid 0 :inputcollid 100 :args ({VAR :varno 1 :varattno 1 :vartype 25 :vartypmod -1 :varcollid 100 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} {CONST :consttype 25 :consttypmod -1 :constcollid 100 :constlen -1 :constbyval false :constisnull true :location -1 :constvalue <>}) :location -1}
{OPEXPR :opno 98 :opfuncid 67 :opresulttype 16 :opretset false :opcollid 0 :inputcollid 100 :args ({VAR :varno 1 :varattno 1 :vartype 25 :vartypmod -1 :varcollid 100 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} {CONST :consttype 25 :consttypmod -1 :constcollid 100 :constlen -1 :constbyval false :constisnull true :location -1 :constvalue <>}) :location -1}
(1 row)
-- print the initial ordering of shard intervals

2
src/test/regress/expected/single_shard_table_udfs.out
View File

@ -121,7 +121,7 @@ FROM pg_dist_partition WHERE logicalrelid = 'null_dist_key_table'::regclass;
SELECT column_name_to_column('null_dist_key_table', 'a');
column_name_to_column
---------------------------------------------------------------------
{VAR :varno 1 :varattno 1 :vartype 23 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1}
{VAR :varno 1 :varattno 1 :vartype 23 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1}
(1 row)
SELECT master_update_shard_statistics(shardid)

12
src/test/regress/expected/start_stop_metadata_sync.out
View File

@ -158,12 +158,12 @@ SELECT * FROM test_matview;
SELECT * FROM pg_dist_partition WHERE logicalrelid::text LIKE 'events%' ORDER BY logicalrelid::text;
logicalrelid | partmethod | partkey | colocationid | repmodel | autoconverted
---------------------------------------------------------------------
events | h | {VAR :varno 1 :varattno 1 :vartype 1184 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 980000 | s | f
events_2021_feb | h | {VAR :varno 1 :varattno 1 :vartype 1184 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 980000 | s | f
events_2021_jan | h | {VAR :varno 1 :varattno 1 :vartype 1184 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 980000 | s | f
events_replicated | h | {VAR :varno 1 :varattno 1 :vartype 1184 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 980001 | c | f
events_replicated_2021_feb | h | {VAR :varno 1 :varattno 1 :vartype 1184 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 980001 | c | f
events_replicated_2021_jan | h | {VAR :varno 1 :varattno 1 :vartype 1184 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 980001 | c | f
events | h | {VAR :varno 1 :varattno 1 :vartype 1184 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 980000 | s | f
events_2021_feb | h | {VAR :varno 1 :varattno 1 :vartype 1184 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 980000 | s | f
events_2021_jan | h | {VAR :varno 1 :varattno 1 :vartype 1184 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 980000 | s | f
events_replicated | h | {VAR :varno 1 :varattno 1 :vartype 1184 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 980001 | c | f
events_replicated_2021_feb | h | {VAR :varno 1 :varattno 1 :vartype 1184 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 980001 | c | f
events_replicated_2021_jan | h | {VAR :varno 1 :varattno 1 :vartype 1184 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1} | 980001 | c | f
(6 rows)
SELECT count(*) > 0 FROM pg_dist_node;

9
src/test/regress/expected/upgrade_basic_after.out
View File

@ -400,3 +400,12 @@ SELECT * FROM t_range ORDER BY id;
(9 rows)
ROLLBACK;
-- There is a difference in partkey Var representation between PG16 and older versions
-- Sanity check here that we can properly do column_to_column_name
SELECT column_to_column_name(logicalrelid, partkey)
FROM pg_dist_partition WHERE partkey IS NOT NULL ORDER BY 1 LIMIT 1;
column_to_column_name
---------------------------------------------------------------------
a
(1 row)

9
src/test/regress/expected/upgrade_basic_before.out
View File

@ -65,3 +65,12 @@ UPDATE pg_dist_shard SET shardminvalue = '1', shardmaxvalue = '3' WHERE shardid
UPDATE pg_dist_shard SET shardminvalue = '5', shardmaxvalue = '7' WHERE shardid = :shardid2;
\copy t_range FROM STDIN with (DELIMITER ',')
\copy t_range FROM STDIN with (DELIMITER ',')
-- There is a difference in partkey Var representation between PG16 and older versions
-- Sanity check here that we can properly do column_to_column_name
SELECT column_to_column_name(logicalrelid, partkey)
FROM pg_dist_partition WHERE partkey IS NOT NULL ORDER BY 1 LIMIT 1;
column_to_column_name
---------------------------------------------------------------------
a
(1 row)

13
src/test/regress/sql/metadata_sync_helpers.sql
View File

@ -798,8 +798,19 @@ BEGIN TRANSACTION ISOLATION LEVEL READ COMMITTED;
SET application_name to 'citus_internal gpid=10000000001';
-- with an ugly trick, update the vartype of table from int to bigint
-- so that making two tables colocated fails
UPDATE pg_dist_partition SET partkey = '{VAR :varno 1 :varattno 1 :vartype 20 :vartypmod -1 :varcollid 0 :varlevelsup 0 :varnoold 1 :varoattno 1 :location -1}'
-- include varnullingrels for PG16
SHOW server_version \gset
SELECT substring(:'server_version', '\d+')::int >= 16 AS server_version_ge_16
\gset
\if :server_version_ge_16
UPDATE pg_dist_partition SET partkey = '{VAR :varno 1 :varattno 1 :vartype 20 :vartypmod -1 :varcollid 0 :varnullingrels (b) :varlevelsup 1 :varnoold 1 :varoattno 1 :location -1}'
WHERE logicalrelid = 'test_2'::regclass;
\else
UPDATE pg_dist_partition SET partkey = '{VAR :varno 1 :varattno 1 :vartype 20 :vartypmod -1 :varcollid 0 :varlevelsup 1 :varnoold 1 :varoattno 1 :location -1}'
WHERE logicalrelid = 'test_2'::regclass;
\endif
SELECT citus_internal_update_relation_colocation('test_2'::regclass, 251);
ROLLBACK;

2
src/test/regress/sql/multi_extension.sql
View File

@ -458,7 +458,7 @@ DELETE FROM pg_dist_shard WHERE shardid = 1;
CREATE TABLE e_transactions(order_id varchar(255) NULL, transaction_id int) PARTITION BY LIST(transaction_id);
CREATE TABLE orders_2020_07_01
PARTITION OF e_transactions FOR VALUES IN (1,2,3);
INSERT INTO pg_dist_partition VALUES ('e_transactions'::regclass,'h', '{VAR :varno 1 :varattno 1 :vartype 1043 :vartypmod 259 :varcollid 100 :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1}', 7, 's');
INSERT INTO pg_dist_partition VALUES ('e_transactions'::regclass,'h', '{VAR :varno 1 :varattno 1 :vartype 1043 :vartypmod 259 :varcollid 100 :varnullingrels (b) :varlevelsup 0 :varnosyn 1 :varattnosyn 1 :location -1}', 7, 's');
SELECT
(metadata->>'partitioned_citus_table_exists_pre_11')::boolean as partitioned_citus_table_exists_pre_11,

5
src/test/regress/sql/upgrade_basic_after.sql
View File

@ -143,3 +143,8 @@ SELECT * FROM t_range ORDER BY id;
ROLLBACK;
-- There is a difference in partkey Var representation between PG16 and older versions
-- Sanity check here that we can properly do column_to_column_name
SELECT column_to_column_name(logicalrelid, partkey)
FROM pg_dist_partition WHERE partkey IS NOT NULL ORDER BY 1 LIMIT 1;

5
src/test/regress/sql/upgrade_basic_before.sql
View File

@ -51,3 +51,8 @@ UPDATE pg_dist_shard SET shardminvalue = '5', shardmaxvalue = '7' WHERE shardid
6,3
7,4
\.
-- There is a difference in partkey Var representation between PG16 and older versions
-- Sanity check here that we can properly do column_to_column_name
SELECT column_to_column_name(logicalrelid, partkey)
FROM pg_dist_partition WHERE partkey IS NOT NULL ORDER BY 1 LIMIT 1;