Do not return NULL for error cases in satisfies_hash_partition().

Since this function is used as a CHECK constraint condition,
returning NULL is tantamount to returning TRUE, which would have the
effect of letting in a row that doesn't satisfy the hash condition.
Admittedly, the cases for which this is done should be unreachable
in practice, but that doesn't make it any less a bad idea.  It also
seems like a dartboard was used to decide which error cases should
throw errors as opposed to returning NULL.

For the checks for NULL input values, I just switched it to returning
false.  There's some argument that an error would be better; but the
case really should be can't-happen in a generated hash constraint,
so it's likely not worth more code for.

For the parent-relation-open-failure case, it seems like we might
as well let relation_open throw an error, instead of having an
impossible-to-diagnose constraint failure.

Back-patch to v11 where this code came in.

Discussion: https://postgr.es/m/24067.1605134819@sss.pgh.pa.us

diff --git a/src/backend/partitioning/partbounds.c b/src/backend/partitioning/partbounds.c
index ac0c495972720b1f0012a6f2b99aa3c4d4ee4d75..299f5deb3290afd54facdd62e5c0765699599d54 100644 (file)
--- a/src/backend/partitioning/partbounds.c
+++ b/src/backend/partitioning/partbounds.c
@@ -4684,6 +4684,8 @@ compute_partition_hash_value(int partnatts, FmgrInfo *partsupfunc, Oid *partcoll
  *
  * Returns true if remainder produced when this computed single hash value is
  * divided by the given modulus is equal to given remainder, otherwise false.
+ * NB: it's important that this never return null, as the constraint machinery
+ * would consider that to be a "pass".
  *
  * See get_qual_for_hash() for usage.
  */
@@ -4708,9 +4710,9 @@ satisfies_hash_partition(PG_FUNCTION_ARGS)
    ColumnsHashData *my_extra;
    uint64      rowHash = 0;
 
-   /* Return null if the parent OID, modulus, or remainder is NULL. */
+   /* Return false if the parent OID, modulus, or remainder is NULL. */
    if (PG_ARGISNULL(0) || PG_ARGISNULL(1) || PG_ARGISNULL(2))
-       PG_RETURN_NULL();
+       PG_RETURN_BOOL(false);
    parentId = PG_GETARG_OID(0);
    modulus = PG_GETARG_INT32(1);
    remainder = PG_GETARG_INT32(2);
@@ -4740,14 +4742,11 @@ satisfies_hash_partition(PG_FUNCTION_ARGS)
        int         j;
 
        /* Open parent relation and fetch partition key info */
-       parent = try_relation_open(parentId, AccessShareLock);
-       if (parent == NULL)
-           PG_RETURN_NULL();
+       parent = relation_open(parentId, AccessShareLock);
        key = RelationGetPartitionKey(parent);
 
        /* Reject parent table that is not hash-partitioned. */
-       if (parent->rd_rel->relkind != RELKIND_PARTITIONED_TABLE ||
-           key->strategy != PARTITION_STRATEGY_HASH)
+       if (key == NULL || key->strategy != PARTITION_STRATEGY_HASH)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("\"%s\" is not a hash partitioned table",

diff --git a/src/test/regress/expected/hash_part.out b/src/test/regress/expected/hash_part.out
index 91ec7c6f589cc48daa1d712af5a4a4d0e93acac5..4c74e4b7069b8d567f42c355538fe9967899b437 100644 (file)
--- a/src/test/regress/expected/hash_part.out
+++ b/src/test/regress/expected/hash_part.out
@@ -10,11 +10,7 @@ CREATE TABLE mchash1
   PARTITION OF mchash FOR VALUES WITH (MODULUS 4, REMAINDER 0);
 -- invalid OID, no such table
 SELECT satisfies_hash_partition(0, 4, 0, NULL);
- satisfies_hash_partition 
---------------------------
- 
-(1 row)
-
+ERROR:  could not open relation with OID 0
 -- not partitioned
 SELECT satisfies_hash_partition('tenk1'::regclass, 4, 0, NULL);
 ERROR:  "tenk1" is not a hash partitioned table
@@ -34,14 +30,14 @@ ERROR:  remainder for hash partition must be less than modulus
 SELECT satisfies_hash_partition('mchash'::regclass, NULL, 0, NULL);
  satisfies_hash_partition 
 --------------------------
- 
+ f
 (1 row)
 
 -- remainder is null
 SELECT satisfies_hash_partition('mchash'::regclass, 4, NULL, NULL);
  satisfies_hash_partition 
 --------------------------
- 
+ f
 (1 row)
 
 -- too many arguments