In 367bc426a1c22b9f6badb06cd41fc438fd034639, I introduced a
CheckIndexCompatible() that approves btree and hash indexes having changed to
a different operator class within the same operator family. To make that
valid, I also tightened the operator family contracts for those access methods
to address casts. However, I've found two retained formal hazards. They're
boring and perhaps unlikely to harm real users, but I'd rather nail them down
just in case.
First, opclasses like array_ops have polymorphic opcintype. Members of such
operator classes could, in general, change behavior arbitrarily in response to
get_fn_expr_argtype(). No core polymorphic operator family member does this.
Nor could they, for no core index access method sets fn_expr. In the absence
of responses to my previous inquiry[1] on the topic, I'm taking the position
that the lack of fn_expr in these calls is an isolated implementation detail
that could change at any time. Therefore, we should only preserve an index of
polymorphic operator class when the old and new opcintype match exactly. This
patch's test suite addition illustrates one ALTER TABLE ALTER TYPE affected by
this new restriction: a conversion from an array type to a domain over that
array type will now require an index rebuild.
Second, as a thought experiment, consider a database with these three types:
1. int4, the core type.
2. int4neg, stores to disk as the negation of its logical value. Includes a
complete set of operators in the integer_ops btree family, but defines no
casts to other integer_ops-represented types.
3. int4other, stores to disk like int4. No operators. Has a implicit binary
coercion cast to int4 and an explicit binary coercion cast to int4neg.
Suppose a table in this database has a column of type int4other with an index
of default operator class. By virtue of the implicit binary coercion and lack
of other candidates, the index will use int4_ops. Now, change the type of
that column from int4other to int4neg. The operator class changes to
int4neg_ops, still within the integer_ops family, and we do not rebuild the
index. However, the logical sign of each value just flipped, making the index
invalid. Where did CheckIndexCompatible() miss? An operator family only
promises cast-compatibility when there exists an implicit or binary coercion
cast between the types in question. There's no int4->int4neg cast here, not
even a multiple-step pathway. CheckIndexCompatible() assumes that our ability
to perform a no-rewrite ALTER TABLE ALTER TYPE implies the existence of such a
cast. It does imply that for the before-and-after _table column types_, but
it's the before-and-after _opcintype_ that matter here.
I think we could close this hazard by having CheckIndexCompatible() test for
an actual implicit or binary coercion cast between the opcintype of the old
and new operator classes. However, I'm not confident to say that no similar
problem would remain. Therefore, I propose ceasing to optimize intra-family
index operator transitions and simply requiring exact matches of operator
classes and exclusion operators. This does not remove any actual optimization
for changes among core types, and it will be simpler to validate. (I designed
the current rules under the misapprehension that varchar_ops was the default
operator class for varchar columns. However, varchar_ops is a copy of
text_ops apart from the name and being non-default. We ship no operator with
a varchar operand, relying instead on binary coercion to text.)
This patch does not, however, remove the new terms from the operator family
contracts. While core PostgreSQL will no longer depend on them, they may
again prove handy for future optimizations like this. I remain of the opinion
that they're already widely (perhaps even universally) obeyed.
This patch conflicts trivially with my patch "Avoid FK validations for
no-rewrite ALTER TABLE ALTER TYPE" in that they both add test cases to the
same location in alter_table.sql. They're otherwise independent, albeit
reflecting parallel principles.
Thanks,
nm
[1]
http://archives.postgresql.org/message-id/20111229211711.ga8...@tornado.leadboat.com
diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index 712b0b0..1bf1de5 100644
*** a/src/backend/commands/indexcmds.c
--- b/src/backend/commands/indexcmds.c
***************
*** 23,28 ****
--- 23,29 ----
#include "catalog/pg_opclass.h"
#include "catalog/pg_opfamily.h"
#include "catalog/pg_tablespace.h"
+ #include "catalog/pg_type.h"
#include "commands/dbcommands.h"
#include "commands/defrem.h"
#include "commands/tablecmds.h"
***************
*** 52,57 ****
--- 53,59 ----
/* non-export function prototypes */
static void CheckPredicate(Expr *predicate);
static void ComputeIndexAttrs(IndexInfo *indexInfo,
+ Oid *typeOidP,
Oid *collationOidP,
Oid *classOidP,
int16 *colOptionP,
***************
*** 87,104 **** static void RangeVarCallbackForReindexIndex(const RangeVar
*relation,
* of columns and that if one has an expression column or predicate, both do.
* Errors arising from the attribute list still apply.
*
! * Most column type changes that can skip a table rewrite will not invalidate
! * indexes. For btree and hash indexes, we assume continued validity when
! * each column of an index would have the same operator family before and
! * after the change. Since we do not document a contract for GIN or GiST
! * operator families, we require an exact operator class match for them and
! * for any other access methods.
! *
! * DefineIndex always verifies that each exclusion operator shares an operator
! * family with its corresponding index operator class. For access methods
! * having no operator family contract, confirm that the old and new indexes
! * use the exact same exclusion operator. For btree and hash, there's nothing
! * more to check.
*
* We do not yet implement a test to verify compatibility of expression
* columns or predicates, so assume any such index is incompatible.
--- 89,105 ----
* of columns and that if one has an expression column or predicate, both do.
* Errors arising from the attribute list still apply.
*
! * Most column type changes that can skip a table rewrite do not invalidate
! * indexes. We ackowledge this when all operator classes, collations and
! * exclusion operators match. Though we could further permit intra-opfamily
! * changes for btree and hash indexes, that adds subtle complexity with no
! * concrete benefit for core types.
!
! * When a comparison or exclusion operator has a polymorphic input type, the
! * actual input types must also match. This defends against the possibility
! * that operators could vary behavior in response to get_fn_expr_argtype().
! * At present, this hazard is theoretical: check_exclusion_constraint() and
! * all core index access methods decline to set fn_expr for such calls.
*
* We do not yet implement a test to verify compatibility of expression
* columns or predicates, so assume any such index is incompatible.
***************
*** 111,116 **** CheckIndexCompatible(Oid oldId,
--- 112,118 ----
List *exclusionOpNames)
{
bool isconstraint;
+ Oid *typeObjectId;
Oid *collationObjectId;
Oid *classObjectId;
Oid accessMethodId;
***************
*** 123,132 **** CheckIndexCompatible(Oid oldId,
int numberOfAttributes;
int old_natts;
bool isnull;
- bool family_am;
bool ret = true;
oidvector *old_indclass;
oidvector *old_indcollation;
int i;
Datum d;
--- 125,134 ----
int numberOfAttributes;
int old_natts;
bool isnull;
bool ret = true;
oidvector *old_indclass;
oidvector *old_indcollation;
+ Relation irel;
int i;
Datum d;
***************
*** 168,177 **** CheckIndexCompatible(Oid oldId,
indexInfo->ii_ExclusionOps = NULL;
indexInfo->ii_ExclusionProcs = NULL;
indexInfo->ii_ExclusionStrats = NULL;
collationObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
classObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
coloptions = (int16 *) palloc(numberOfAttributes * sizeof(int16));
! ComputeIndexAttrs(indexInfo, collationObjectId, classObjectId,
coloptions, attributeList,
exclusionOpNames, relationId,
accessMethodName, accessMethodId,
--- 170,181 ----
indexInfo->ii_ExclusionOps = NULL;
indexInfo->ii_ExclusionProcs = NULL;
indexInfo->ii_ExclusionStrats = NULL;
+ typeObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
collationObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
classObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
coloptions = (int16 *) palloc(numberOfAttributes * sizeof(int16));
! ComputeIndexAttrs(indexInfo,
! typeObjectId, collationObjectId,
classObjectId,
coloptions, attributeList,
exclusionOpNames, relationId,
accessMethodName, accessMethodId,
***************
*** 191,202 **** CheckIndexCompatible(Oid oldId,
return false;
}
! /*
! * If the old and new operator class of any index column differ in
! * operator family or collation, regard the old index as incompatible.
! * For access methods other than btree and hash, a family match has no
! * defined meaning; require an exact operator class match.
! */
old_natts = ((Form_pg_index) GETSTRUCT(tuple))->indnatts;
Assert(old_natts == numberOfAttributes);
--- 195,201 ----
return false;
}
! /* Any change in operator class or collation breaks compatibility. */
old_natts = ((Form_pg_index) GETSTRUCT(tuple))->indnatts;
Assert(old_natts == numberOfAttributes);
***************
*** 208,259 **** CheckIndexCompatible(Oid oldId,
Assert(!isnull);
old_indclass = (oidvector *) DatumGetPointer(d);
! family_am = accessMethodId == BTREE_AM_OID || accessMethodId ==
HASH_AM_OID;
!
! for (i = 0; i < old_natts; i++)
! {
! Oid old_class = old_indclass->values[i];
! Oid new_class = classObjectId[i];
!
! if (!(old_indcollation->values[i] == collationObjectId[i]
! && (old_class == new_class
! || (family_am &&
(get_opclass_family(old_class)
! ==
get_opclass_family(new_class))))))
! {
! ret = false;
! break;
! }
! }
ReleaseSysCache(tuple);
! /*
! * For btree and hash, exclusion operators need only fall in the same
! * operator family; ComputeIndexAttrs already verified that much. If we
! * get this far, we know that the index operator family has not changed,
! * and we're done. For other access methods, require exact matches for
! * all exclusion operators.
! */
! if (ret && !family_am && indexInfo->ii_ExclusionOps != NULL)
{
- Relation irel;
Oid *old_operators, *old_procs;
uint16 *old_strats;
- /* Caller probably already holds a stronger lock. */
- irel = index_open(oldId, AccessShareLock);
RelationGetExclusionInfo(irel, &old_operators, &old_procs,
&old_strats);
! for (i = 0; i < old_natts; i++)
! if (old_operators[i] != indexInfo->ii_ExclusionOps[i])
! {
! ret = false;
! break;
! }
! index_close(irel, NoLock);
}
return ret;
}
--- 207,248 ----
Assert(!isnull);
old_indclass = (oidvector *) DatumGetPointer(d);
! ret = (memcmp(old_indclass->values, classObjectId,
! old_natts * sizeof(Oid)) == 0 &&
! memcmp(old_indcollation->values, collationObjectId,
! old_natts * sizeof(Oid)) == 0);
ReleaseSysCache(tuple);
! /* For polymorphic opcintype, column type changes break compatibility.
*/
! irel = index_open(oldId, AccessShareLock); /* caller probably has a
lock */
! for (i = 0; i < old_natts && ret; i++)
! ret =
(!IsPolymorphicType(get_opclass_input_type(classObjectId[i])) ||
! irel->rd_att->attrs[i]->atttypid == typeObjectId[i]);
!
! /* Any change in exclusion operator selections breaks compatibility. */
! if (ret && indexInfo->ii_ExclusionOps != NULL)
{
Oid *old_operators, *old_procs;
uint16 *old_strats;
RelationGetExclusionInfo(irel, &old_operators, &old_procs,
&old_strats);
+ ret = memcmp(old_operators, indexInfo->ii_ExclusionOps,
+ old_natts * sizeof(Oid)) == 0;
! /* Require an exact input type match for polymorphic operators.
*/
! for (i = 0; i < old_natts && ret; i++)
! {
! Oid left,
! right;
! op_input_types(indexInfo->ii_ExclusionOps[i], &left,
&right);
! ret = (!(IsPolymorphicType(left) ||
IsPolymorphicType(right)) ||
! irel->rd_att->attrs[i]->atttypid ==
typeObjectId[i]);
! }
}
+ index_close(irel, NoLock);
return ret;
}
***************
*** 315,320 **** DefineIndex(RangeVar *heapRelation,
--- 304,310 ----
bool quiet,
bool concurrent)
{
+ Oid *typeObjectId;
Oid *collationObjectId;
Oid *classObjectId;
Oid accessMethodId;
***************
*** 550,559 **** DefineIndex(RangeVar *heapRelation,
indexInfo->ii_Concurrent = concurrent;
indexInfo->ii_BrokenHotChain = false;
collationObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
classObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
coloptions = (int16 *) palloc(numberOfAttributes * sizeof(int16));
! ComputeIndexAttrs(indexInfo, collationObjectId, classObjectId,
coloptions, attributeList,
exclusionOpNames, relationId,
accessMethodName, accessMethodId,
--- 540,551 ----
indexInfo->ii_Concurrent = concurrent;
indexInfo->ii_BrokenHotChain = false;
+ typeObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
collationObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
classObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
coloptions = (int16 *) palloc(numberOfAttributes * sizeof(int16));
! ComputeIndexAttrs(indexInfo,
! typeObjectId, collationObjectId,
classObjectId,
coloptions, attributeList,
exclusionOpNames, relationId,
accessMethodName, accessMethodId,
***************
*** 980,985 **** CheckPredicate(Expr *predicate)
--- 972,978 ----
*/
static void
ComputeIndexAttrs(IndexInfo *indexInfo,
+ Oid *typeOidP,
Oid *collationOidP,
Oid *classOidP,
int16 *colOptionP,
***************
*** 1108,1113 **** ComputeIndexAttrs(IndexInfo *indexInfo,
--- 1101,1108 ----
}
}
+ typeOidP[attn] = atttype;
+
/*
* Apply collation override if any
*/
diff --git a/src/test/regress/expected/index 57096f2..5e11d3b 100644
*** a/src/test/regress/expected/alter_table.out
--- b/src/test/regress/expected/alter_table.out
***************
*** 1656,1661 **** where oid = 'test_storage'::regclass;
--- 1656,1671 ----
t
(1 row)
+ -- SET DATA TYPE without a rewrite
+ SET client_min_messages = debug1;
+ CREATE DOMAIN other_textarr AS text[];
+ CREATE TABLE norewrite_array(c text[] PRIMARY KEY);
+ NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index
"norewrite_array_pkey" for table "norewrite_array"
+ DEBUG: building index "norewrite_array_pkey" on table "norewrite_array"
+ ALTER TABLE norewrite_array ALTER c TYPE text[]; -- no work
+ ALTER TABLE norewrite_array ALTER c TYPE other_textarr; -- rebuild index
+ DEBUG: building index "norewrite_array_pkey" on table "norewrite_array"
+ RESET client_min_messages;
--
-- lock levels
--
diff --git a/src/test/regress/sql/alter_table.sqindex faafb22..b546134 100644
*** a/src/test/regress/sql/alter_table.sql
--- b/src/test/regress/sql/alter_table.sql
***************
*** 1190,1195 **** select reltoastrelid <> 0 as has_toast_table
--- 1190,1203 ----
from pg_class
where oid = 'test_storage'::regclass;
+ -- SET DATA TYPE without a rewrite
+ SET client_min_messages = debug1;
+ CREATE DOMAIN other_textarr AS text[];
+ CREATE TABLE norewrite_array(c text[] PRIMARY KEY);
+ ALTER TABLE norewrite_array ALTER c TYPE text[]; -- no work
+ ALTER TABLE norewrite_array ALTER c TYPE other_textarr; -- rebuild index
+ RESET client_min_messages;
+
--
-- lock levels
--
--
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