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Remove logic for converting a table to a view.

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Up to now we have allowed manual creation of an ON SELECT rule on
a table to convert it into a view.  That was never anything but a
horrid, error-prone hack though.  pg_dump used to rely on that
behavior to deal with cases involving circular dependencies,
where a dependency loop could be broken by separating the creation
of a view from installation of its ON SELECT rule.  However, we
changed pg_dump to use CREATE OR REPLACE VIEW for that in commit
d8c05aff5 (which was later back-patched as far as 9.4), so there's
not a good argument anymore for continuing to support the behavior.

The proximate reason for axing it now is that we found that the
new statistics code has failure modes associated with the relkind
change caused by this behavior.  We'll patch around that in v15,
but going forward it seems like a better idea to get rid of the
need to support relkind changes.

Discussion: https://postgr.es/m/CALDaNm2yXz+zOtv7y5zBd5WKT8O0Ld3YxikuU3dcyCvxF7gypA@mail.gmail.com
This commit is contained in:
Tom Lane 2022-12-02 12:14:32 -05:00
parent 66456da150
commit b23cd185fd
8 changed files with 45 additions and 305 deletions
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28
doc/src/sgml/rules.sgml
View File

@ -280,14 +280,16 @@
<para>
Views in <productname>PostgreSQL</productname> are implemented
using the rule system. In fact, there is essentially no difference
between:
using the rule system. A view is basically an empty table (having no
actual storage) with an <literal>ON SELECT DO INSTEAD</literal> rule.
Conventionally, that rule is named <literal>_RETURN</literal>.
So a view like
<programlisting>
CREATE VIEW myview AS SELECT * FROM mytab;
</programlisting>
compared against the two commands:
is very nearly the same thing as
<programlisting>
CREATE TABLE myview (<replaceable>same column list as mytab</replaceable>);
@ -295,13 +297,17 @@ CREATE RULE "_RETURN" AS ON SELECT TO myview DO INSTEAD
SELECT * FROM mytab;
</programlisting>
because this is exactly what the <command>CREATE VIEW</command>
command does internally. This has some side effects. One of them
is that the information about a view in the
<productname>PostgreSQL</productname> system catalogs is exactly
the same as it is for a table. So for the parser, there is
absolutely no difference between a table and a view. They are the
same thing: relations.
although you can't actually write that, because tables are not
allowed to have <literal>ON SELECT</literal> rules.
</para>
<para>
A view can also have other kinds of <literal>DO INSTEAD</literal>
rules, allowing <command>INSERT</command>, <command>UPDATE</command>,
or <command>DELETE</command> commands to be performed on the view
despite its lack of underlying storage.
This is discussed further below, in
<xref linkend="rules-views-update"/>.
</para>
<sect2 id="rules-select">
@ -1111,7 +1117,7 @@ SELECT word FROM words ORDER BY word &lt;-&gt; 'caterpiler' LIMIT 10;
<para>
Rules that are defined on <command>INSERT</command>, <command>UPDATE</command>,
and <command>DELETE</command> are significantly different from the view rules
described in the previous section. First, their <command>CREATE
described in the previous sections. First, their <command>CREATE
RULE</command> command allows more:
<itemizedlist>

189
src/backend/rewrite/rewriteDefine.c
View File

@ -239,7 +239,6 @@ DefineQueryRewrite(const char *rulename,
Relation event_relation;
ListCell *l;
Query *query;
bool RelisBecomingView = false;
Oid ruleId = InvalidOid;
ObjectAddress address;
@ -311,7 +310,18 @@ DefineQueryRewrite(const char *rulename,
/*
* Rules ON SELECT are restricted to view definitions
*
* So there cannot be INSTEAD NOTHING, ...
* So this had better be a view, ...
*/
if (event_relation->rd_rel->relkind != RELKIND_VIEW &&
event_relation->rd_rel->relkind != RELKIND_MATVIEW)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("relation \"%s\" cannot have ON SELECT rules",
RelationGetRelationName(event_relation)),
errdetail_relkind_not_supported(event_relation->rd_rel->relkind)));
/*
* ... there cannot be INSTEAD NOTHING, ...
*/
if (action == NIL)
ereport(ERROR,
@ -407,93 +417,6 @@ DefineQueryRewrite(const char *rulename,
ViewSelectRuleName)));
rulename = pstrdup(ViewSelectRuleName);
}
/*
* Are we converting a relation to a view?
*
* If so, check that the relation is empty because the storage for the
* relation is going to be deleted. Also insist that the rel not be
* involved in partitioning, nor have any triggers, indexes, child or
* parent tables, RLS policies, or RLS enabled. (Note: some of these
* tests are too strict, because they will reject relations that once
* had such but don't anymore. But we don't really care, because this
* whole business of converting relations to views is just an obsolete
* kluge to allow dump/reload of views that participate in circular
* dependencies.)
*/
if (event_relation->rd_rel->relkind != RELKIND_VIEW &&
event_relation->rd_rel->relkind != RELKIND_MATVIEW)
{
TableScanDesc scanDesc;
Snapshot snapshot;
TupleTableSlot *slot;
if (event_relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("cannot convert partitioned table \"%s\" to a view",
RelationGetRelationName(event_relation))));
/* only case left: */
Assert(event_relation->rd_rel->relkind == RELKIND_RELATION);
if (event_relation->rd_rel->relispartition)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("cannot convert partition \"%s\" to a view",
RelationGetRelationName(event_relation))));
snapshot = RegisterSnapshot(GetLatestSnapshot());
scanDesc = table_beginscan(event_relation, snapshot, 0, NULL);
slot = table_slot_create(event_relation, NULL);
if (table_scan_getnextslot(scanDesc, ForwardScanDirection, slot))
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("could not convert table \"%s\" to a view because it is not empty",
RelationGetRelationName(event_relation))));
ExecDropSingleTupleTableSlot(slot);
table_endscan(scanDesc);
UnregisterSnapshot(snapshot);
if (event_relation->rd_rel->relhastriggers)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("could not convert table \"%s\" to a view because it has triggers",
RelationGetRelationName(event_relation)),
errhint("In particular, the table cannot be involved in any foreign key relationships.")));
if (event_relation->rd_rel->relhasindex)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("could not convert table \"%s\" to a view because it has indexes",
RelationGetRelationName(event_relation))));
if (event_relation->rd_rel->relhassubclass)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("could not convert table \"%s\" to a view because it has child tables",
RelationGetRelationName(event_relation))));
if (has_superclass(RelationGetRelid(event_relation)))
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("could not convert table \"%s\" to a view because it has parent tables",
RelationGetRelationName(event_relation))));
if (event_relation->rd_rel->relrowsecurity)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("could not convert table \"%s\" to a view because it has row security enabled",
RelationGetRelationName(event_relation))));
if (relation_has_policies(event_relation))
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("could not convert table \"%s\" to a view because it has row security policies",
RelationGetRelationName(event_relation))));
RelisBecomingView = true;
}
}
else
{
@ -569,94 +492,6 @@ DefineQueryRewrite(const char *rulename,
SetRelationRuleStatus(event_relid, true);
}
/* ---------------------------------------------------------------------
* If the relation is becoming a view:
* - delete the associated storage files
* - get rid of any system attributes in pg_attribute; a view shouldn't
* have any of those
* - remove the toast table; there is no need for it anymore, and its
* presence would make vacuum slightly more complicated
* - set relkind to RELKIND_VIEW, and adjust other pg_class fields
* to be appropriate for a view
*
* NB: we had better have AccessExclusiveLock to do this ...
* ---------------------------------------------------------------------
*/
if (RelisBecomingView)
{
Relation relationRelation;
Oid toastrelid;
HeapTuple classTup;
Form_pg_class classForm;
relationRelation = table_open(RelationRelationId, RowExclusiveLock);
toastrelid = event_relation->rd_rel->reltoastrelid;
/* drop storage while table still looks like a table */
RelationDropStorage(event_relation);
DeleteSystemAttributeTuples(event_relid);
/*
* Drop the toast table if any. (This won't take care of updating the
* toast fields in the relation's own pg_class entry; we handle that
* below.)
*/
if (OidIsValid(toastrelid))
{
ObjectAddress toastobject;
/*
* Delete the dependency of the toast relation on the main
* relation so we can drop the former without dropping the latter.
*/
deleteDependencyRecordsFor(RelationRelationId, toastrelid,
false);
/* Make deletion of dependency record visible */
CommandCounterIncrement();
/* Now drop toast table, including its index */
toastobject.classId = RelationRelationId;
toastobject.objectId = toastrelid;
toastobject.objectSubId = 0;
performDeletion(&toastobject, DROP_RESTRICT,
PERFORM_DELETION_INTERNAL);
}
/*
* SetRelationRuleStatus may have updated the pg_class row, so we must
* advance the command counter before trying to update it again.
*/
CommandCounterIncrement();
/*
* Fix pg_class entry to look like a normal view's, including setting
* the correct relkind and removal of reltoastrelid of the toast table
* we potentially removed above.
*/
classTup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(event_relid));
if (!HeapTupleIsValid(classTup))
elog(ERROR, "cache lookup failed for relation %u", event_relid);
classForm = (Form_pg_class) GETSTRUCT(classTup);
classForm->relam = InvalidOid;
classForm->reltablespace = InvalidOid;
classForm->relpages = 0;
classForm->reltuples = -1;
classForm->relallvisible = 0;
classForm->reltoastrelid = InvalidOid;
classForm->relhasindex = false;
classForm->relkind = RELKIND_VIEW;
classForm->relfrozenxid = InvalidTransactionId;
classForm->relminmxid = InvalidMultiXactId;
classForm->relreplident = REPLICA_IDENTITY_NOTHING;
CatalogTupleUpdate(relationRelation, &classTup->t_self, classTup);
heap_freetuple(classTup);
table_close(relationRelation, RowExclusiveLock);
}
ObjectAddressSet(address, RewriteRelationId, ruleId);
/* Close rel, but keep lock till commit... */

8
src/test/modules/test_ddl_deparse/expected/create_rule.out
View File

@ -1,6 +1,8 @@
---
--- CREATE_RULE
---
--- Note: views' ON SELECT rules are tested elsewhere.
---
CREATE RULE rule_1 AS
ON INSERT
TO datatype_table
@ -16,12 +18,6 @@ CREATE RULE rule_3 AS
TO datatype_table
DO ALSO NOTHING;
NOTICE: DDL test: type simple, tag CREATE RULE
CREATE RULE "_RETURN" AS
ON SELECT
TO like_datatype_table
DO INSTEAD
SELECT * FROM datatype_view;
NOTICE: DDL test: type simple, tag CREATE RULE
CREATE RULE rule_3 AS
ON DELETE
TO like_datatype_table

8
src/test/modules/test_ddl_deparse/sql/create_rule.sql
View File

@ -1,6 +1,8 @@
---
--- CREATE_RULE
---
--- Note: views' ON SELECT rules are tested elsewhere.
---
CREATE RULE rule_1 AS
@ -18,12 +20,6 @@ CREATE RULE rule_3 AS
TO datatype_table
DO ALSO NOTHING;
CREATE RULE "_RETURN" AS
ON SELECT
TO like_datatype_table
DO INSTEAD
SELECT * FROM datatype_view;
CREATE RULE rule_3 AS
ON DELETE
TO like_datatype_table

22
src/test/regress/expected/rowsecurity.out
View File

@ -3942,28 +3942,6 @@ DROP ROLE regress_rls_frank; -- succeeds
ROLLBACK TO q;
ROLLBACK; -- cleanup
--
-- Converting table to view
--
BEGIN;
CREATE TABLE t (c int);
CREATE POLICY p ON t USING (c % 2 = 1);
ALTER TABLE t ENABLE ROW LEVEL SECURITY;
SAVEPOINT q;
CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD
SELECT * FROM generate_series(1,5) t0(c); -- fails due to row-level security enabled
ERROR: could not convert table "t" to a view because it has row security enabled
ROLLBACK TO q;
ALTER TABLE t DISABLE ROW LEVEL SECURITY;
SAVEPOINT q;
CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD
SELECT * FROM generate_series(1,5) t0(c); -- fails due to policy p on t
ERROR: could not convert table "t" to a view because it has row security policies
ROLLBACK TO q;
DROP POLICY p ON t;
CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD
SELECT * FROM generate_series(1,5) t0(c); -- succeeds
ROLLBACK;
--
-- Policy expression handling
--
BEGIN;

46
src/test/regress/expected/rules.out
View File

@ -2707,54 +2707,26 @@ ERROR: cannot drop rule _RETURN on view rules_fooview because view rules_foovie
HINT: You can drop view rules_fooview instead.
drop view rules_fooview;
--
-- test conversion of table to view (needed to load some pg_dump files)
-- We used to allow converting a table to a view by creating a "_RETURN"
-- rule for it, but no more.
--
create table rules_fooview (x int, y text);
select xmin, * from rules_fooview;
xmin | x | y
------+---+---
(0 rows)
create rule "_RETURN" as on select to rules_fooview do instead
select 1 as x, 'aaa'::text as y;
select * from rules_fooview;
x | y
---+-----
1 | aaa
(1 row)
select xmin, * from rules_fooview; -- fail, views don't have such a column
ERROR: column "xmin" does not exist
LINE 1: select xmin, * from rules_fooview;
^
select reltoastrelid, relkind, relfrozenxid
from pg_class where oid = 'rules_fooview'::regclass;
reltoastrelid | relkind | relfrozenxid
---------------+---------+--------------
0 | v | 0
(1 row)
drop view rules_fooview;
-- cannot convert an inheritance parent or child to a view, though
create table rules_fooview (x int, y text);
create table rules_fooview_child () inherits (rules_fooview);
create rule "_RETURN" as on select to rules_fooview do instead
select 1 as x, 'aaa'::text as y;
ERROR: could not convert table "rules_fooview" to a view because it has child tables
create rule "_RETURN" as on select to rules_fooview_child do instead
select 1 as x, 'aaa'::text as y;
ERROR: could not convert table "rules_fooview_child" to a view because it has parent tables
drop table rules_fooview cascade;
NOTICE: drop cascades to table rules_fooview_child
ERROR: relation "rules_fooview" cannot have ON SELECT rules
DETAIL: This operation is not supported for tables.
drop table rules_fooview;
-- likewise, converting a partitioned table or partition to view is not allowed
create table rules_fooview (x int, y text) partition by list (x);
create rule "_RETURN" as on select to rules_fooview do instead
select 1 as x, 'aaa'::text as y;
ERROR: cannot convert partitioned table "rules_fooview" to a view
ERROR: relation "rules_fooview" cannot have ON SELECT rules
DETAIL: This operation is not supported for partitioned tables.
create table rules_fooview_part partition of rules_fooview for values in (1);
create rule "_RETURN" as on select to rules_fooview_part do instead
select 1 as x, 'aaa'::text as y;
ERROR: cannot convert partition "rules_fooview_part" to a view
ERROR: relation "rules_fooview_part" cannot have ON SELECT rules
DETAIL: This operation is not supported for tables.
drop table rules_fooview;
--
-- check for planner problems with complex inherited UPDATES

24
src/test/regress/sql/rowsecurity.sql
View File

@ -1713,30 +1713,6 @@ ROLLBACK TO q;
ROLLBACK; -- cleanup
--
-- Converting table to view
--
BEGIN;
CREATE TABLE t (c int);
CREATE POLICY p ON t USING (c % 2 = 1);
ALTER TABLE t ENABLE ROW LEVEL SECURITY;
SAVEPOINT q;
CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD
SELECT * FROM generate_series(1,5) t0(c); -- fails due to row-level security enabled
ROLLBACK TO q;
ALTER TABLE t DISABLE ROW LEVEL SECURITY;
SAVEPOINT q;
CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD
SELECT * FROM generate_series(1,5) t0(c); -- fails due to policy p on t
ROLLBACK TO q;
DROP POLICY p ON t;
CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD
SELECT * FROM generate_series(1,5) t0(c); -- succeeds
ROLLBACK;
--
-- Policy expression handling
--

25
src/test/regress/sql/rules.sql
View File

@ -884,33 +884,14 @@ drop rule "_RETURN" on rules_fooview;
drop view rules_fooview;
--
-- test conversion of table to view (needed to load some pg_dump files)
-- We used to allow converting a table to a view by creating a "_RETURN"
-- rule for it, but no more.
--
create table rules_fooview (x int, y text);
select xmin, * from rules_fooview;
create rule "_RETURN" as on select to rules_fooview do instead
select 1 as x, 'aaa'::text as y;
select * from rules_fooview;
select xmin, * from rules_fooview; -- fail, views don't have such a column
select reltoastrelid, relkind, relfrozenxid
from pg_class where oid = 'rules_fooview'::regclass;
drop view rules_fooview;
-- cannot convert an inheritance parent or child to a view, though
create table rules_fooview (x int, y text);
create table rules_fooview_child () inherits (rules_fooview);
create rule "_RETURN" as on select to rules_fooview do instead
select 1 as x, 'aaa'::text as y;
create rule "_RETURN" as on select to rules_fooview_child do instead
select 1 as x, 'aaa'::text as y;
drop table rules_fooview cascade;
drop table rules_fooview;
-- likewise, converting a partitioned table or partition to view is not allowed
create table rules_fooview (x int, y text) partition by list (x);