/*
* get_table_colocation_id returns colocation id of given distributed table.
*/
Datum
get_table_colocation_id(PG_FUNCTION_ARGS)
{
Oid distributedTableId = PG_GETARG_OID(0);
uint32 colocationId = TableColocationId(distributedTableId);
PG_RETURN_INT32(colocationId);
}
/*
* ErrorIfUnsupportedForeignConstraint runs checks related to foreign constraints and
* errors out if it is not possible to create one of the foreign constraint in distributed
* environment.
*
* To support foreign constraints, we require that;
* - If referencing and referenced tables are hash-distributed
* - Referencing and referenced tables are co-located.
* - Foreign constraint is defined over distribution column.
* - ON DELETE/UPDATE SET NULL, ON DELETE/UPDATE SET DEFAULT and ON UPDATE CASCADE options
* are not used.
* - Replication factors of referencing and referenced table are 1.
* - If referenced table is a reference table
* - ON DELETE/UPDATE SET NULL, ON DELETE/UPDATE SET DEFAULT and ON UPDATE CASCADE options
* are not used on the distribution key of the referencing column.
* - If referencing table is a reference table, error out
*/
void
ErrorIfUnsupportedForeignConstraint(Relation relation, char distributionMethod,
Var *distributionColumn, uint32 colocationId)
{
Relation pgConstraint = NULL;
SysScanDesc scanDescriptor = NULL;
ScanKeyData scanKey[1];
int scanKeyCount = 1;
HeapTuple heapTuple = NULL;
Oid referencingTableId = relation->rd_id;
Oid referencedTableId = InvalidOid;
uint32 referencedTableColocationId = INVALID_COLOCATION_ID;
Var *referencedTablePartitionColumn = NULL;
Datum referencingColumnsDatum = 0;
Datum *referencingColumnArray = NULL;
int referencingColumnCount = 0;
Datum referencedColumnsDatum = 0;
Datum *referencedColumnArray = NULL;
int referencedColumnCount = 0;
bool isNull = false;
int attrIdx = 0;
bool foreignConstraintOnPartitionColumn = false;
bool selfReferencingTable = false;
bool referencedTableIsAReferenceTable = false;
bool referencingColumnsIncludeDistKey = false;
pgConstraint = heap_open(ConstraintRelationId, AccessShareLock);
ScanKeyInit(&scanKey[0], Anum_pg_constraint_conrelid, BTEqualStrategyNumber, F_OIDEQ,
relation->rd_id);
scanDescriptor = systable_beginscan(pgConstraint, ConstraintRelidIndexId, true, NULL,
scanKeyCount, scanKey);
heapTuple = systable_getnext(scanDescriptor);
while (HeapTupleIsValid(heapTuple))
{
Form_pg_constraint constraintForm = (Form_pg_constraint) GETSTRUCT(heapTuple);
bool singleReplicatedTable = true;
if (constraintForm->contype != CONSTRAINT_FOREIGN)
{
heapTuple = systable_getnext(scanDescriptor);
continue;
}
/*
* We should make this check in this loop because the error message will only
* be given if the table has a foreign constraint and the table is a reference
* table.
*/
if (distributionMethod == DISTRIBUTE_BY_NONE)
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot create foreign key constraint because "
"reference tables are not supported as the "
"referencing table of a foreign constraint"),
errdetail("Reference tables are only supported as the "
"referenced table of a foreign key when the "
"referencing table is a hash distributed "
"table")));
}
referencedTableId = constraintForm->confrelid;
selfReferencingTable = referencingTableId == referencedTableId;
/*
* Some checks are not meaningful if foreign key references the table itself.
* Therefore we will skip those checks.
*/
if (!selfReferencingTable)
{
if (!IsDistributedTable(referencedTableId))
{
ereport(ERROR, (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
errmsg("cannot create foreign key constraint"),
errdetail("Referenced table must be a distributed "
"table.")));
}
/*
* PartitionMethod errors out when it is called for non-distributed
* tables. This is why we make this check under !selfReferencingTable
* and after !IsDistributedTable(referencedTableId).
*/
if (PartitionMethod(referencedTableId) == DISTRIBUTE_BY_NONE)
{
referencedTableIsAReferenceTable = true;
}
/*
* To enforce foreign constraints, tables must be co-located unless a
* reference table is referenced.
*/
referencedTableColocationId = TableColocationId(referencedTableId);
if (colocationId == INVALID_COLOCATION_ID ||
(colocationId != referencedTableColocationId &&
!referencedTableIsAReferenceTable))
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot create foreign key constraint since "
"relations are not colocated or not referencing "
"a reference table"),
errdetail(
"A distributed table can only have foreign keys "
"if it is referencing another colocated hash "
"distributed table or a reference table")));
}
referencedTablePartitionColumn = DistPartitionKey(referencedTableId);
}
else
{
/*
* If the referenced table is not a reference table, the distribution
* column in referencing table should be the distribution column in
* referenced table as well.
*/
referencedTablePartitionColumn = distributionColumn;
}
/*
* Column attributes are not available in Form_pg_constraint, therefore we need
* to find them in the system catalog. After finding them, we iterate over column
* attributes together because partition column must be at the same place in both
* referencing and referenced side of the foreign key constraint
*/
referencingColumnsDatum = SysCacheGetAttr(CONSTROID, heapTuple,
Anum_pg_constraint_conkey, &isNull);
referencedColumnsDatum = SysCacheGetAttr(CONSTROID, heapTuple,
Anum_pg_constraint_confkey, &isNull);
deconstruct_array(DatumGetArrayTypeP(referencingColumnsDatum), INT2OID, 2, true,
's', &referencingColumnArray, NULL, &referencingColumnCount);
deconstruct_array(DatumGetArrayTypeP(referencedColumnsDatum), INT2OID, 2, true,
's', &referencedColumnArray, NULL, &referencedColumnCount);
Assert(referencingColumnCount == referencedColumnCount);
for (attrIdx = 0; attrIdx < referencingColumnCount; ++attrIdx)
{
AttrNumber referencingAttrNo = DatumGetInt16(referencingColumnArray[attrIdx]);
AttrNumber referencedAttrNo = DatumGetInt16(referencedColumnArray[attrIdx]);
if (distributionColumn->varattno == referencingAttrNo &&
(!referencedTableIsAReferenceTable &&
referencedTablePartitionColumn->varattno == referencedAttrNo))
{
foreignConstraintOnPartitionColumn = true;
}
if (distributionColumn->varattno == referencingAttrNo)
{
referencingColumnsIncludeDistKey = true;
}
}
/*
* If columns in the foreign key includes the distribution key from the
* referencing side, we do not allow update/delete operations through
* foreign key constraints (e.g. ... ON UPDATE SET NULL)
*/
if (referencingColumnsIncludeDistKey)
{
/*
* ON DELETE SET NULL and ON DELETE SET DEFAULT is not supported. Because we do
* not want to set partition column to NULL or default value.
*/
if (constraintForm->confdeltype == FKCONSTR_ACTION_SETNULL ||
constraintForm->confdeltype == FKCONSTR_ACTION_SETDEFAULT)
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot create foreign key constraint"),
errdetail("SET NULL or SET DEFAULT is not supported"
" in ON DELETE operation when distribution "
"key is included in the foreign key constraint")));
}
/*
* ON UPDATE SET NULL, ON UPDATE SET DEFAULT and UPDATE CASCADE is not supported.
* Because we do not want to set partition column to NULL or default value. Also
* cascading update operation would require re-partitioning. Updating partition
* column value is not allowed anyway even outside of foreign key concept.
*/
if (constraintForm->confupdtype == FKCONSTR_ACTION_SETNULL ||
constraintForm->confupdtype == FKCONSTR_ACTION_SETDEFAULT ||
constraintForm->confupdtype == FKCONSTR_ACTION_CASCADE)
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot create foreign key constraint"),
errdetail("SET NULL, SET DEFAULT or CASCADE is not "
"supported in ON UPDATE operation when "
"distribution key included in the foreign "
"constraint.")));
}
}
/*
* if tables are hash-distributed and colocated, we need to make sure that
* the distribution key is included in foreign constraint.
*/
if (!referencedTableIsAReferenceTable && !foreignConstraintOnPartitionColumn)
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot create foreign key constraint"),
errdetail("Foreign keys are supported in two cases, "
"either in between two colocated tables including "
"partition column in the same ordinal in the both "
"tables or from distributed to reference tables")));
}
/*
* We do not allow to create foreign constraints if shard replication factor is
* greater than 1. Because in our current design, multiple replicas may cause
* locking problems and inconsistent shard contents.
*
* Note that we allow referenced table to be a reference table (e.g., not a
* single replicated table). This is allowed since (a) we are sure that
* placements always be in the same state (b) executors are aware of reference
* tables and handle concurrency related issues accordingly.
*/
if (IsDistributedTable(referencingTableId))
{
/* check whether ALTER TABLE command is applied over single replicated table */
if (!SingleReplicatedTable(referencingTableId))
{
singleReplicatedTable = false;
}
}
else
{
Assert(distributionMethod == DISTRIBUTE_BY_HASH);
/* check whether creating single replicated table with foreign constraint */
if (ShardReplicationFactor > 1)
{
singleReplicatedTable = false;
}
}
if (!singleReplicatedTable)
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot create foreign key constraint"),
errdetail("Citus Community Edition currently supports "
"foreign key constraints only for "
"\"citus.shard_replication_factor = 1\"."),
errhint("Please change \"citus.shard_replication_factor to "
"1\". To learn more about using foreign keys with "
"other replication factors, please contact us at "
"https://citusdata.com/about/contact_us.")));
}
heapTuple = systable_getnext(scanDescriptor);
}
/* clean up scan and close system catalog */
systable_endscan(scanDescriptor);
heap_close(pgConstraint, AccessShareLock);
}
