Rethink definition of pg_attribute.attcompression.

Redefine '\0' (InvalidCompressionMethod) as meaning "if we need to
compress, use the current setting of default_toast_compression".
This allows '\0' to be a suitable default choice regardless of
datatype, greatly simplifying code paths that initialize tupledescs
and the like.  It seems like a more user-friendly approach as well,
because now the default compression choice doesn't migrate into table
definitions, meaning that changing default_toast_compression is
usually sufficient to flip an installation's behavior; one needn't
tediously issue per-column ALTER SET COMPRESSION commands.

Along the way, fix a few minor bugs and documentation issues
with the per-column-compression feature.  Adopt more robust
APIs for SetIndexStorageProperties and GetAttributeCompression.

Bump catversion because typical contents of attcompression will now
be different.  We could get away without doing that, but it seems
better to ensure v14 installations all agree on this.  (We already
forced initdb for beta2, anyway.)

Discussion: https://postgr.es/m/626613.1621787110@sss.pgh.pa.us

1 files changed, 20 insertions, 18 deletions

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index aaf1a51f685..9ee90e3f13a 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -561,6 +561,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 %type <node>	TableConstraint TableLikeClause
 %type <ival>	TableLikeOptionList TableLikeOption
+%type <str>		column_compression opt_column_compression
 %type <list>	ColQualList
 %type <node>	ColConstraint ColConstraintElem ConstraintAttr
 %type <ival>	key_actions key_delete key_match key_update key_action
@@ -609,7 +610,6 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <list>		hash_partbound
 %type <defelt>		hash_partbound_elem
 
-%type <str>	optColumnCompression
 
 /*
  * Non-keyword token types.  These are hard-wired into the "flex" lexer.
@@ -2302,6 +2302,15 @@ alter_table_cmd:
 					n->def = (Node *) makeString($6);
 					$$ = (Node *)n;
 				}
+			/* ALTER TABLE <name> ALTER [COLUMN] <colname> SET COMPRESSION <cm> */
+			| ALTER opt_column ColId SET column_compression
+				{
+					AlterTableCmd *n = makeNode(AlterTableCmd);
+					n->subtype = AT_SetCompression;
+					n->name = $3;
+					n->def = (Node *) makeString($5);
+					$$ = (Node *)n;
+				}
 			/* ALTER TABLE <name> ALTER [COLUMN] <colname> ADD GENERATED ... AS IDENTITY ... */
 			| ALTER opt_column ColId ADD_P GENERATED generated_when AS IDENTITY_P OptParenthesizedSeqOptList
 				{
@@ -2346,15 +2355,6 @@ alter_table_cmd:
 					n->missing_ok = true;
 					$$ = (Node *)n;
 				}
-			/* ALTER TABLE <name> ALTER [COLUMN] <colname> SET (COMPRESSION <cm>) */
-			| ALTER opt_column ColId SET optColumnCompression
-				{
-					AlterTableCmd *n = makeNode(AlterTableCmd);
-					n->subtype = AT_SetCompression;
-					n->name = $3;
-					n->def = (Node *) makeString($5);
-					$$ = (Node *)n;
-				}
 			/* ALTER TABLE <name> DROP [COLUMN] IF EXISTS <colname> [RESTRICT|CASCADE] */
 			| DROP opt_column IF_P EXISTS ColId opt_drop_behavior
 				{
@@ -3462,7 +3462,7 @@ TypedTableElement:
 			| TableConstraint					{ $$ = $1; }
 		;
 
-columnDef:	ColId Typename optColumnCompression create_generic_options ColQualList
+columnDef:	ColId Typename opt_column_compression create_generic_options ColQualList
 				{
 					ColumnDef *n = makeNode(ColumnDef);
 					n->colname = $1;
@@ -3522,13 +3522,15 @@ columnOptions:	ColId ColQualList
 				}
 		;
 
-optColumnCompression:
-					COMPRESSION name
-					{
-						$$ = $2;
-					}
-					| /*EMPTY*/	{ $$ = NULL; }
-				;
+column_compression:
+			COMPRESSION ColId						{ $$ = $2; }
+			| COMPRESSION DEFAULT					{ $$ = pstrdup("default"); }
+		;
+
+opt_column_compression:
+			column_compression						{ $$ = $1; }
+			| /*EMPTY*/								{ $$ = NULL; }
+		;
 
 ColQualList:
 			ColQualList ColConstraint				{ $$ = lappend($1, $2); }