Disallow unlogged materialized views.

The initial implementation of this feature was really unsupportable,
because it's relying on the physical size of an on-disk file to carry the
relation's populated/unpopulated state, which is at least a modularity
violation and could have serious long-term consequences.  We could say that
an unlogged matview goes to empty on crash, but not everybody likes that
definition, so let's just remove the feature for 9.3.  We can add it back
when we have a less klugy implementation.

I left the grammar and tab-completion support for CREATE UNLOGGED
MATERIALIZED VIEW in place, since it's harmless and allows delivering a
more specific error message about the unsupported feature.

I'm committing this separately to ease identification of what should be
reverted when/if we are able to re-enable the feature.

Author: tglsfdc

doc/src/sgml/ref/create_materialized_view.sgml

@@ -21,7 +21,7 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-CREATE [ UNLOGGED ] MATERIALIZED VIEW <replaceable>table_name</replaceable>
+CREATE MATERIALIZED VIEW <replaceable>table_name</replaceable>
     [ (<replaceable>column_name</replaceable> [, ...] ) ]
     [ WITH ( <replaceable class="PARAMETER">storage_parameter</replaceable> [= <replaceable class="PARAMETER">value</replaceable>] [, ... ] ) ]
     [ TABLESPACE <replaceable class="PARAMETER">tablespace_name</replaceable> ]
@@ -54,16 +54,6 @@ CREATE [ UNLOGGED ] MATERIALIZED VIEW <replaceable>table_name</replaceable>
   <title>Parameters</title>
 
   <variablelist>
-   <varlistentry>
-    <term><literal>UNLOGGED</></term>
-    <listitem>
-     <para>
-      If specified, the materialized view will be unlogged.
-      Refer to <xref linkend="sql-createtable"> for details.
-     </para>
-    </listitem>
-   </varlistentry>
-
    <varlistentry>
     <term><replaceable>table_name</replaceable></term>
     <listitem>

src/backend/parser/analyze.c

@@ -2166,6 +2166,18 @@ transformCreateTableAsStmt(ParseState *pstate, CreateTableAsStmt *stmt)
 					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 					 errmsg("materialized views may not be defined using bound parameters")));
 
+		/*
+		 * For now, we disallow unlogged materialized views, because it
+		 * seems like a bad idea for them to just go to empty after a crash.
+		 * (If we could mark them as unpopulated, that would be better, but
+		 * that requires catalog changes which crash recovery can't presently
+		 * handle.)
+		 */
+		if (stmt->into->rel->relpersistence == RELPERSISTENCE_UNLOGGED)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("materialized views cannot be UNLOGGED")));
+
 		/*
 		 * At runtime, we'll need a copy of the parsed-but-not-rewritten Query
 		 * for purposes of creating the view's ON SELECT rule.  We stash that

src/test/regress/expected/matview.out

@@ -279,59 +279,8 @@ SELECT * FROM tvvm;
 (1 row)
 
 -- test diemv when the mv does not exist
-DROP MATERIALIZED VIEW IF EXISTS tum;
-NOTICE:  materialized view "tum" does not exist, skipping
--- make sure that an unlogged materialized view works (in the absence of a crash)
-CREATE UNLOGGED MATERIALIZED VIEW tum AS SELECT type, sum(amt) AS totamt FROM t GROUP BY type WITH NO DATA;
-SELECT pg_relation_is_scannable('tum'::regclass);
- pg_relation_is_scannable 
---------------------------
- f
-(1 row)
-
-SELECT * FROM tum;
-ERROR:  materialized view "tum" has not been populated
-HINT:  Use the REFRESH MATERIALIZED VIEW command.
-REFRESH MATERIALIZED VIEW tum;
-SELECT pg_relation_is_scannable('tum'::regclass);
- pg_relation_is_scannable 
---------------------------
- t
-(1 row)
-
-SELECT * FROM tum;
- type | totamt 
-------+--------
- y    |     12
- z    |     24
- x    |      5
-(3 rows)
-
-REFRESH MATERIALIZED VIEW tum WITH NO DATA;
-SELECT pg_relation_is_scannable('tum'::regclass);
- pg_relation_is_scannable 
---------------------------
- f
-(1 row)
-
-SELECT * FROM tum;
-ERROR:  materialized view "tum" has not been populated
-HINT:  Use the REFRESH MATERIALIZED VIEW command.
-REFRESH MATERIALIZED VIEW tum WITH DATA;
-SELECT pg_relation_is_scannable('tum'::regclass);
- pg_relation_is_scannable 
---------------------------
- t
-(1 row)
-
-SELECT * FROM tum;
- type | totamt 
-------+--------
- y    |     12
- z    |     24
- x    |      5
-(3 rows)
-
+DROP MATERIALIZED VIEW IF EXISTS no_such_mv;
+NOTICE:  materialized view "no_such_mv" does not exist, skipping
 -- test join of mv and view
 SELECT type, m.totamt AS mtot, v.totamt AS vtot FROM tm m LEFT JOIN tv v USING (type) ORDER BY type;
  type | mtot | vtot 
@@ -341,8 +290,6 @@ SELECT type, m.totamt AS mtot, v.totamt AS vtot FROM tm m LEFT JOIN tv v USING (
  z    |   24 |   24
 (3 rows)
 
--- test diemv when the mv does exist
-DROP MATERIALIZED VIEW IF EXISTS tum;
 -- make sure that dependencies are reported properly when they block the drop
 DROP TABLE t;
 ERROR:  cannot drop table t because other objects depend on it

src/test/regress/sql/matview.sql

@@ -87,28 +87,11 @@ SELECT * FROM tvmm;
 SELECT * FROM tvvm;
 
 -- test diemv when the mv does not exist
-DROP MATERIALIZED VIEW IF EXISTS tum;
-
--- make sure that an unlogged materialized view works (in the absence of a crash)
-CREATE UNLOGGED MATERIALIZED VIEW tum AS SELECT type, sum(amt) AS totamt FROM t GROUP BY type WITH NO DATA;
-SELECT pg_relation_is_scannable('tum'::regclass);
-SELECT * FROM tum;
-REFRESH MATERIALIZED VIEW tum;
-SELECT pg_relation_is_scannable('tum'::regclass);
-SELECT * FROM tum;
-REFRESH MATERIALIZED VIEW tum WITH NO DATA;
-SELECT pg_relation_is_scannable('tum'::regclass);
-SELECT * FROM tum;
-REFRESH MATERIALIZED VIEW tum WITH DATA;
-SELECT pg_relation_is_scannable('tum'::regclass);
-SELECT * FROM tum;
+DROP MATERIALIZED VIEW IF EXISTS no_such_mv;
 
 -- test join of mv and view
 SELECT type, m.totamt AS mtot, v.totamt AS vtot FROM tm m LEFT JOIN tv v USING (type) ORDER BY type;
 
--- test diemv when the mv does exist
-DROP MATERIALIZED VIEW IF EXISTS tum;
-
 -- make sure that dependencies are reported properly when they block the drop
 DROP TABLE t;