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Fix deadlock adding named constraint with long partition name (#7799) #8540

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Merged
codeforall merged 6 commits into from
Apr 30, 2026
Merged

Fix deadlock adding named constraint with long partition name (#7799) #8540

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cd90ec1
Fix deadlock adding named constraint with long partition name (#7799)
codeforall Apr 8, 2026
9cfd6a8
Merge branch 'main' into muusama/7799
ihalatci Apr 16, 2026
1d482ec
Merge branch 'main' into muusama/7799
codeforall Apr 30, 2026
3ab67c2
Address review comments: extend comment and add EXCLUDE/FK tests
codeforall Apr 30, 2026
b3f7aae
Guard EXCLUDE test with PG17+ version check and add alternate output …
codeforall Apr 30, 2026
e1b7135
Fix PG16 alternate output: include command text inside version-guarde…
codeforall Apr 30, 2026
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36 changes: 36 additions & 0 deletions src/backend/distributed/commands/table.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1000,6 +1000,28 @@ SwitchToSequentialAndLocalExecutionIfConstraintNameTooLong(Oid relationId,
return;
}

/*
* For non-index constraints (CHECK, FOREIGN KEY), PostgreSQL propagates
* the exact same constraint name from the parent to all partition children
* (see ATAddCheckConstraint and addFkConstraint in tablecmds.c). Since
* user-provided identifiers are already bounded by NAMEDATALEN at parse
* time, the inherited name can never be too long on partition shards.
*
* This also correctly handles unnamed non-index constraints whose
* conname was assigned by PrepareAlterTableStmtForConstraint(), since
* those generated names are also bounded by NAMEDATALEN.
*
* Only index-backed constraints (PRIMARY KEY, UNIQUE, EXCLUDE) need this
* check because PostgreSQL auto-generates new names for partition child
* indexes based on the partition table name (see generateClonedIndexStmt
* in parse_utilcmd.c which sets idxname = NULL), and those generated
* names can exceed NAMEDATALEN when the partition name is long.
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@colm-mchugh colm-mchugh Apr 30, 2026

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nit: the check also (correctly) applies to handling unnamed non-index constraints (e.g., unnamed CHECK) whose conname was assigned by PrepareAlterTableStmtForConstraint() earlier, right ? Those generated names are also bounded by NAMEDATALEN, so this early return is correct for them too. How about extending the comment to describe that also, with something like:

 * This also correctly handles unnamed non-index constraints whose 
 * conname was assigned by PrepareAlterTableStmtForConstraint(), since
 * those generated names are also bounded by NAMEDATALEN.

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@codeforall codeforall Apr 30, 2026

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Good catch! I've extended the comment to document this.

*/
if (constraint->conname != NULL && !ConstrTypeUsesIndex(constraint->contype))
{
return;
}

char *longestPartitionShardName = get_rel_name(longestNamePartitionId);
ShardInterval *shardInterval = LoadShardIntervalWithLongestShardName(
longestNamePartitionId);
Expand Down Expand Up @@ -1375,6 +1397,9 @@ PreprocessAlterTableStmt(Node *node, const char *alterTableCommand,
leftRelationId,
constraint);
}

SwitchToSequentialAndLocalExecutionIfConstraintNameTooLong(
leftRelationId, constraint);
}

/*
Expand All @@ -1397,6 +1422,17 @@ PreprocessAlterTableStmt(Node *node, const char *alterTableCommand,
constraint);
}
}
else if (constraint->conname != NULL)
{
/*
* When the user provides an explicit constraint name, we still
* need to check if the resulting constraint name on the shards
* of partitions would be too long, and if so, switch to
* sequential execution to prevent self-deadlocks.
*/
SwitchToSequentialAndLocalExecutionIfConstraintNameTooLong(
leftRelationId, constraint);
}
}
else if (alterTableType == AT_DropConstraint)
{
Expand Down
173 changes: 173 additions & 0 deletions src/test/regress/expected/multi_alter_table_add_constraints.out
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Expand Up @@ -701,6 +701,179 @@ DROP SCHEMA sc3 CASCADE;
NOTICE: drop cascades to 2 other objects
DETAIL: drop cascades to table sc3.alter_add_prim_key
drop cascades to table sc3.alter_add_unique
-- Test that named constraints on partitioned tables with long partition names
-- switch to sequential execution to prevent self-deadlocks (issue #7799)
CREATE SCHEMA test_named_constraint_long_partition;
SET search_path TO 'test_named_constraint_long_partition';
CREATE TABLE dist_partitioned_table (dist_col int, another_col int, partition_col timestamp)
PARTITION BY RANGE (partition_col);
CREATE TABLE p1 PARTITION OF dist_partitioned_table
FOR VALUES FROM ('2021-01-01') TO ('2022-01-01');
CREATE TABLE longlonglonglonglonglonglonglonglonglonglonglonglonglonglongabc
PARTITION OF dist_partitioned_table
FOR VALUES FROM ('2020-01-01') TO ('2021-01-01');
SELECT create_distributed_table('dist_partitioned_table', 'partition_col');
create_distributed_table
---------------------------------------------------------------------

(1 row)

-- Check "ADD CONSTRAINT ... PRIMARY KEY" with explicit name switches to sequential
SET client_min_messages TO DEBUG1;
ALTER TABLE dist_partitioned_table ADD CONSTRAINT my_pk PRIMARY KEY(partition_col);
DEBUG: the constraint name on the shards of the partition is too long, switching to sequential and local execution mode to prevent self deadlocks: longlonglonglonglonglonglonglonglonglonglonglo_537570f5_14_pkey
DEBUG: ALTER TABLE / ADD PRIMARY KEY will create implicit index "my_pk" for table "dist_partitioned_table"
DEBUG: ALTER TABLE / ADD PRIMARY KEY will create implicit index "longlonglonglonglonglonglonglonglonglonglonglonglonglonglo_pkey" for table "longlonglonglonglonglonglonglonglonglonglonglonglonglonglongabc"
DEBUG: ALTER TABLE / ADD PRIMARY KEY will create implicit index "p1_pkey" for table "p1"
DEBUG: verifying table "p1"
DEBUG: verifying table "longlonglonglonglonglonglonglonglonglonglonglonglonglonglongabc"
RESET client_min_messages;
-- Verify constraint is created on the coordinator
SELECT con.conname
FROM pg_catalog.pg_constraint con
INNER JOIN pg_catalog.pg_class rel ON rel.oid = con.conrelid
INNER JOIN pg_catalog.pg_namespace nsp ON nsp.oid = rel.relnamespace
WHERE rel.relname = 'dist_partitioned_table'
AND con.contype = 'p';
conname
---------------------------------------------------------------------
my_pk
(1 row)

ALTER TABLE dist_partitioned_table DROP CONSTRAINT my_pk;
-- Check "ADD CONSTRAINT ... UNIQUE" with explicit name switches to sequential
SET client_min_messages TO DEBUG1;
ALTER TABLE dist_partitioned_table ADD CONSTRAINT my_uq UNIQUE(partition_col);
DEBUG: the constraint name on the shards of the partition is too long, switching to sequential and local execution mode to prevent self deadlocks: longlonglonglonglonglonglonglonglonglonglongl_partition_col_key
DEBUG: ALTER TABLE / ADD UNIQUE will create implicit index "my_uq" for table "dist_partitioned_table"
DEBUG: ALTER TABLE / ADD UNIQUE will create implicit index "longlonglonglonglonglonglonglonglonglonglongl_partition_col_key" for table "longlonglonglonglonglonglonglonglonglonglonglonglonglonglongabc"
DEBUG: ALTER TABLE / ADD UNIQUE will create implicit index "p1_partition_col_key" for table "p1"
RESET client_min_messages;
SELECT con.conname
FROM pg_catalog.pg_constraint con
INNER JOIN pg_catalog.pg_class rel ON rel.oid = con.conrelid
INNER JOIN pg_catalog.pg_namespace nsp ON nsp.oid = rel.relnamespace
WHERE rel.relname = 'dist_partitioned_table'
AND con.contype = 'u';
conname
---------------------------------------------------------------------
my_uq
(1 row)

ALTER TABLE dist_partitioned_table DROP CONSTRAINT my_uq;
-- Check "ADD CONSTRAINT ... CHECK" with explicit name does NOT switch to sequential
-- because PG propagates the user-provided name to partitions as-is (no auto-generation)
SET client_min_messages TO DEBUG1;
ALTER TABLE dist_partitioned_table ADD CONSTRAINT my_chk CHECK(dist_col > another_col);
DEBUG: verifying table "p1"
DEBUG: verifying table "longlonglonglonglonglonglonglonglonglonglonglonglonglonglongabc"
RESET client_min_messages;
SELECT con.conname
FROM pg_catalog.pg_constraint con
INNER JOIN pg_catalog.pg_class rel ON rel.oid = con.conrelid
INNER JOIN pg_catalog.pg_namespace nsp ON nsp.oid = rel.relnamespace
WHERE rel.relname = 'dist_partitioned_table'
AND con.contype = 'c';
conname
---------------------------------------------------------------------
my_chk
(1 row)

ALTER TABLE dist_partitioned_table DROP CONSTRAINT my_chk;
-- Check "ADD CONSTRAINT ... EXCLUDE" with explicit name switches to sequential
-- because PG auto-generates new index names on partitions (same as PK/UNIQUE)
-- EXCLUDE on partitioned tables is only supported in PG17+
SHOW server_version \gset
SELECT substring(:'server_version', '\d+')::int >= 17 AS server_version_ge_17
\gset
\if :server_version_ge_17
SET client_min_messages TO DEBUG1;
ALTER TABLE dist_partitioned_table ADD CONSTRAINT my_excl EXCLUDE USING btree (partition_col WITH =);
DEBUG: the constraint name on the shards of the partition is too long, switching to sequential and local execution mode to prevent self deadlocks: longlonglonglonglonglonglonglonglonglonglong_partition_col_excl
DEBUG: ALTER TABLE / ADD EXCLUDE will create implicit index "my_excl" for table "dist_partitioned_table"
DEBUG: ALTER TABLE / ADD EXCLUDE will create implicit index "longlonglonglonglonglonglonglonglonglonglong_partition_col_excl" for table "longlonglonglonglonglonglonglonglonglonglonglonglonglonglongabc"
DEBUG: ALTER TABLE / ADD EXCLUDE will create implicit index "p1_partition_col_excl" for table "p1"
RESET client_min_messages;
SELECT con.conname
FROM pg_catalog.pg_constraint con
INNER JOIN pg_catalog.pg_class rel ON rel.oid = con.conrelid
INNER JOIN pg_catalog.pg_namespace nsp ON nsp.oid = rel.relnamespace
WHERE rel.relname = 'dist_partitioned_table'
AND con.contype = 'x';
conname
---------------------------------------------------------------------
my_excl
(1 row)

ALTER TABLE dist_partitioned_table DROP CONSTRAINT my_excl;
\endif
-- Check "ADD CONSTRAINT ... FOREIGN KEY" with explicit name does NOT switch to
-- sequential because PG propagates the user-provided name to partitions as-is
-- FK requires shard_replication_factor = 1, so create a separate table for this test
SET citus.shard_replication_factor TO 1;
CREATE TABLE fk_dist_partitioned_table (dist_col int, another_col int, partition_col timestamp)
PARTITION BY RANGE (partition_col);
CREATE TABLE fk_p1 PARTITION OF fk_dist_partitioned_table
FOR VALUES FROM ('2021-01-01') TO ('2022-01-01');
CREATE TABLE fk_longlonglonglonglonglonglonglonglonglonglonglonglonglongabc
PARTITION OF fk_dist_partitioned_table
FOR VALUES FROM ('2020-01-01') TO ('2021-01-01');
SELECT create_distributed_table('fk_dist_partitioned_table', 'partition_col');
create_distributed_table
---------------------------------------------------------------------

(1 row)

CREATE TABLE ref_table (ref_col timestamp PRIMARY KEY);
SELECT create_reference_table('ref_table');
create_reference_table
---------------------------------------------------------------------

(1 row)

SET client_min_messages TO DEBUG1;
ALTER TABLE fk_dist_partitioned_table ADD CONSTRAINT my_fk FOREIGN KEY (partition_col) REFERENCES ref_table(ref_col);
RESET client_min_messages;
SELECT con.conname
FROM pg_catalog.pg_constraint con
INNER JOIN pg_catalog.pg_class rel ON rel.oid = con.conrelid
INNER JOIN pg_catalog.pg_namespace nsp ON nsp.oid = rel.relnamespace
WHERE rel.relname = 'fk_dist_partitioned_table'
AND con.contype = 'f';
conname
---------------------------------------------------------------------
my_fk
(1 row)

ALTER TABLE fk_dist_partitioned_table DROP CONSTRAINT my_fk;
RESET citus.shard_replication_factor;
-- Check that we error out when adding a named constraint in a transaction block
-- after a parallel query has already been executed
BEGIN;
SELECT count(*) FROM dist_partitioned_table;
count
---------------------------------------------------------------------
0
(1 row)

ALTER TABLE dist_partitioned_table ADD CONSTRAINT my_pk PRIMARY KEY(partition_col);
ERROR: The constraint name (longlonglonglonglonglonglonglonglonglonglonglo_537570f5_14_pkey) on a shard is too long and could lead to deadlocks when executed in a transaction block after a parallel query
HINT: Try re-running the transaction with "SET LOCAL citus.multi_shard_modify_mode TO 'sequential';"
ROLLBACK;
-- try inside a sequential block -- should succeed
BEGIN;
SET LOCAL citus.multi_shard_modify_mode TO 'sequential';
SELECT count(*) FROM dist_partitioned_table;
count
---------------------------------------------------------------------
0
(1 row)

ALTER TABLE dist_partitioned_table ADD CONSTRAINT my_pk PRIMARY KEY(partition_col);
ROLLBACK;
SET client_min_messages TO ERROR;
DROP SCHEMA test_named_constraint_long_partition CASCADE;
SET search_path TO 'public';
CREATE SCHEMA test_auto_explain;
SET search_path TO 'test_auto_explain';
-- Test ALTER TABLE ... ADD CONSTRAINT ... does not cause a crash when auto_explain module is loaded
Expand Down
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