Improve error, on ALTER TABLE SET DISTRIBUTED BY on non-hashable type.

Old error:

ERROR:  cannot use expression as distribution key, because it is not hashable (cdbmutate.c:1329)

The new error is the same you get with CREATE TABLE. While we're at it,
also change "can't" contraction to "cannot" in the error message, to
follow the PostgreSQL error message guidelines.

src/backend/commands/tablecmds.c

@@ -15163,6 +15163,7 @@ ATExecSetDistributedBy(Relation rel, Node *node, AlterTableCmd *cmd)
 					char	   *colName = strVal((Value *)lfirst(lc));
 					HeapTuple	tuple;
 					AttrNumber	attnum;
+					Form_pg_attribute attform;
 
 					tuple = SearchSysCacheAttName(RelationGetRelid(rel), colName);
 
@@ -15172,8 +15173,8 @@ ATExecSetDistributedBy(Relation rel, Node *node, AlterTableCmd *cmd)
 								 errmsg("column \"%s\" of relation \"%s\" does not exist",
 										colName,
 										RelationGetRelationName(rel))));
-
-					attnum = ((Form_pg_attribute) GETSTRUCT(tuple))->attnum;
+					attform = (Form_pg_attribute) GETSTRUCT(tuple);
+					attnum = attform->attnum;
 
 					/* Prevent them from altering a system attribute */
 					if (attnum <= 0)
@@ -15182,6 +15183,15 @@ ATExecSetDistributedBy(Relation rel, Node *node, AlterTableCmd *cmd)
 								 errmsg("cannot distribute by system column \"%s\"",
 										colName)));
 
+					/* The attribute must be hashable. */
+					if (!isGreenplumDbHashable(attform->atttypid))
+					{
+						ereport(ERROR,
+								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+								 errmsg("type \"%s\" cannot be a part of a distribution key",
+										format_type_be(attform->atttypid))));
+					}
+
 					policykeys = lappend_int(policykeys, attnum);
 
 					ReleaseSysCache(tuple);

src/backend/parser/parse_utilcmd.c

@@ -2141,8 +2141,7 @@ transformDistributedBy(CreateStmtContext *cxt,
 						{
 							ereport(ERROR,
 									(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-									 errmsg("type \"%s\" can't be a part of a "
-										 "distribution key",
+									 errmsg("type \"%s\" cannot be a part of a distribution key",
 										 format_type_be(typeOid))));
 						}
 

src/test/regress/expected/qp_gist_indexes3.out

@@ -239,13 +239,17 @@ CREATE UNIQUE INDEX ShouldNotExist ON gisttable_pktest USING GiST (poli);
 ERROR:  access method "gist" does not support unique indexes
 CREATE UNIQUE INDEX ShouldNotExist ON gisttable_pktest USING GiST (bullseye);
 ERROR:  access method "gist" does not support unique indexes
--- Test whether geometric types can be part of a primary key.
+-- Test whether geometric types can be part of a distribution key.
 CREATE TABLE GistTable2 (id INTEGER, property BOX) DISTRIBUTED BY (property);
-ERROR:  type "box" can't be a part of a distribution key
+ERROR:  type "box" cannot be a part of a distribution key
 CREATE TABLE GistTable2 (id INTEGER, poli POLYGON) DISTRIBUTED BY (poli);
-ERROR:  type "polygon" can't be a part of a distribution key
+ERROR:  type "polygon" cannot be a part of a distribution key
 CREATE TABLE GistTable2 (id INTEGER, bullseye CIRCLE) DISTRIBUTED BY (bullseye);
-ERROR:  type "circle" can't be a part of a distribution key
+ERROR:  type "circle" cannot be a part of a distribution key
+-- Same with ALTER TABLE.
+CREATE TABLE GistTable2 (id INTEGER, property BOX) DISTRIBUTED RANDOMLY;
+ALTER TABLE GistTable2 SET DISTRIBUTED BY (property);
+ERROR:  type "box" cannot be a part of a distribution key
 -- ----------------------------------------------------------------------
 -- Test: test09NegativeTests.sql
 -- ----------------------------------------------------------------------
@@ -287,11 +291,12 @@ ERROR:  hash indexes are not supported
 -- ----------------------------------------------------------------------
 -- start_ignore
 drop schema qp_gist_indexes3 cascade;
-NOTICE:  drop cascades to 6 other objects
+NOTICE:  drop cascades to 7 other objects
 DETAIL:  drop cascades to table gisttable3
 drop cascades to function to_box(text)
 drop cascades to function insertintogisttable3(integer)
 drop cascades to function insertmanyintogisttable3(integer,integer)
 drop cascades to table gisttable_pktest
+drop cascades to table gisttable2
 drop cascades to table gisttable14
 -- end_ignore

src/test/regress/expected/qp_gist_indexes3_optimizer.out

@@ -243,13 +243,17 @@ CREATE UNIQUE INDEX ShouldNotExist ON gisttable_pktest USING GiST (poli);
 ERROR:  access method "gist" does not support unique indexes
 CREATE UNIQUE INDEX ShouldNotExist ON gisttable_pktest USING GiST (bullseye);
 ERROR:  access method "gist" does not support unique indexes
--- Test whether geometric types can be part of a primary key.
+-- Test whether geometric types can be part of a distribution key.
 CREATE TABLE GistTable2 (id INTEGER, property BOX) DISTRIBUTED BY (property);
-ERROR:  type "box" can't be a part of a distribution key
+ERROR:  type "box" cannot be a part of a distribution key
 CREATE TABLE GistTable2 (id INTEGER, poli POLYGON) DISTRIBUTED BY (poli);
-ERROR:  type "polygon" can't be a part of a distribution key
+ERROR:  type "polygon" cannot be a part of a distribution key
 CREATE TABLE GistTable2 (id INTEGER, bullseye CIRCLE) DISTRIBUTED BY (bullseye);
-ERROR:  type "circle" can't be a part of a distribution key
+ERROR:  type "circle" cannot be a part of a distribution key
+-- Same with ALTER TABLE.
+CREATE TABLE GistTable2 (id INTEGER, property BOX) DISTRIBUTED RANDOMLY;
+ALTER TABLE GistTable2 SET DISTRIBUTED BY (property);
+ERROR:  type "box" cannot be a part of a distribution key
 -- ----------------------------------------------------------------------
 -- Test: test09NegativeTests.sql
 -- ----------------------------------------------------------------------
@@ -291,11 +295,12 @@ ERROR:  hash indexes are not supported
 -- ----------------------------------------------------------------------
 -- start_ignore
 drop schema qp_gist_indexes3 cascade;
-NOTICE:  drop cascades to 6 other objects
+NOTICE:  drop cascades to 7 other objects
 DETAIL:  drop cascades to table gisttable3
 drop cascades to function to_box(text)
 drop cascades to function insertintogisttable3(integer)
 drop cascades to function insertmanyintogisttable3(integer,integer)
 drop cascades to table gisttable_pktest
+drop cascades to table gisttable2
 drop cascades to table gisttable14
 -- end_ignore

src/test/regress/sql/qp_gist_indexes3.sql

@@ -211,11 +211,15 @@ CREATE UNIQUE INDEX ShouldNotExist ON gisttable_pktest USING GiST (poli);
 CREATE UNIQUE INDEX ShouldNotExist ON gisttable_pktest USING GiST (bullseye);
 
 
--- Test whether geometric types can be part of a primary key.
+-- Test whether geometric types can be part of a distribution key.
 CREATE TABLE GistTable2 (id INTEGER, property BOX) DISTRIBUTED BY (property);
 CREATE TABLE GistTable2 (id INTEGER, poli POLYGON) DISTRIBUTED BY (poli);
 CREATE TABLE GistTable2 (id INTEGER, bullseye CIRCLE) DISTRIBUTED BY (bullseye);
 
+-- Same with ALTER TABLE.
+CREATE TABLE GistTable2 (id INTEGER, property BOX) DISTRIBUTED RANDOMLY;
+ALTER TABLE GistTable2 SET DISTRIBUTED BY (property);
+
 -- ----------------------------------------------------------------------
 -- Test: test09NegativeTests.sql
 -- ----------------------------------------------------------------------