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Apply table and domain CHECK constraints in name order.

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Previously, CHECK constraints of the same scope were checked in whatever
order they happened to be read from pg_constraint.  (Usually, but not
reliably, this would be creation order for domain constraints and reverse
creation order for table constraints, because of differing implementation
details.)  Nondeterministic results of this sort are problematic at least
for testing purposes, and in discussion it was agreed to be a violation of
the principle of least astonishment.  Therefore, borrow the principle
already established for triggers, and apply such checks in name order
(using strcmp() sort rules).  This lets users control the check order
if they have a mind to.

Domain CHECK constraints still follow the rule of checking lower nested
domains' constraints first; the name sort only applies to multiple
constraints attached to the same domain.

In passing, I failed to resist the temptation to wordsmith a bit in
create_domain.sgml.

Apply to HEAD only, since this could result in a behavioral change in
existing applications, and the potential regression test failures have
not actually been observed in our buildfarm.
This commit is contained in:
Tom Lane
2015-03-23 16:59:29 -04:00
parent 871293fb7f
commit e5f455f59f
6 changed files with 129 additions and 24 deletions
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61
src/backend/utils/cache/typcache.c vendored
View File

@ -149,6 +149,7 @@ static int32 NextRecordTypmod = 0; /* number of entries used */
static void load_typcache_tupdesc(TypeCacheEntry *typentry);
static void load_rangetype_info(TypeCacheEntry *typentry);
static void load_domaintype_info(TypeCacheEntry *typentry);
static int dcs_cmp(const void *a, const void *b);
static void decr_dcc_refcount(DomainConstraintCache *dcc);
static void dccref_deletion_callback(void *arg);
static bool array_element_has_equality(TypeCacheEntry *typentry);
@ -650,6 +651,8 @@ load_domaintype_info(TypeCacheEntry *typentry)
Oid typeOid = typentry->type_id;
DomainConstraintCache *dcc;
bool notNull = false;
DomainConstraintState **ccons;
int cconslen;
Relation conRel;
MemoryContext oldcxt;
@ -666,9 +669,12 @@ load_domaintype_info(TypeCacheEntry *typentry)
/*
* We try to optimize the common case of no domain constraints, so don't
* create the dcc object and context until we find a constraint.
* create the dcc object and context until we find a constraint. Likewise
* for the temp sorting array.
*/
dcc = NULL;
ccons = NULL;
cconslen = 0;
/*
* Scan pg_constraint for relevant constraints. We want to find
@ -682,6 +688,7 @@ load_domaintype_info(TypeCacheEntry *typentry)
HeapTuple tup;
HeapTuple conTup;
Form_pg_type typTup;
int nccons = 0;
ScanKeyData key[1];
SysScanDesc scan;
@ -763,17 +770,45 @@ load_domaintype_info(TypeCacheEntry *typentry)
r->name = pstrdup(NameStr(c->conname));
r->check_expr = ExecInitExpr(check_expr, NULL);
/*
* Use lcons() here because constraints of parent domains should
* be applied earlier.
*/
dcc->constraints = lcons(r, dcc->constraints);
MemoryContextSwitchTo(oldcxt);
/* Accumulate constraints in an array, for sorting below */
if (ccons == NULL)
{
cconslen = 8;
ccons = (DomainConstraintState **)
palloc(cconslen * sizeof(DomainConstraintState *));
}
else if (nccons >= cconslen)
{
cconslen *= 2;
ccons = (DomainConstraintState **)
repalloc(ccons, cconslen * sizeof(DomainConstraintState *));
}
ccons[nccons++] = r;
}
systable_endscan(scan);
if (nccons > 0)
{
/*
* Sort the items for this domain, so that CHECKs are applied in a
* deterministic order.
*/
if (nccons > 1)
qsort(ccons, nccons, sizeof(DomainConstraintState *), dcs_cmp);
/*
* Now attach them to the overall list. Use lcons() here because
* constraints of parent domains should be applied earlier.
*/
oldcxt = MemoryContextSwitchTo(dcc->dccContext);
while (nccons > 0)
dcc->constraints = lcons(ccons[--nccons], dcc->constraints);
MemoryContextSwitchTo(oldcxt);
}
/* loop to next domain in stack */
typeOid = typTup->typbasetype;
ReleaseSysCache(tup);
@ -836,6 +871,18 @@ load_domaintype_info(TypeCacheEntry *typentry)
typentry->flags |= TCFLAGS_CHECKED_DOMAIN_CONSTRAINTS;
}
/*
* qsort comparator to sort DomainConstraintState pointers by name
*/
static int
dcs_cmp(const void *a, const void *b)
{
const DomainConstraintState *const * ca = (const DomainConstraintState *const *) a;
const DomainConstraintState *const * cb = (const DomainConstraintState *const *) b;
return strcmp((*ca)->name, (*cb)->name);
}
/*
* decr_dcc_refcount --- decrement a DomainConstraintCache's refcount,
* and free it if no references remain