Re-order pg_attribute columns to eliminate some padding space.

Now that attcompression is just a char, there's a lot of wasted
padding space after it.  Move it into the group of char-wide
columns to save a net of 4 bytes per pg_attribute entry.  While
we're at it, swap the order of attstorage and attalign to make for
a more logical grouping of these columns.

Also re-order actions in related code to match the new field ordering.

This patch also fixes one outright bug: equalTupleDescs() failed to
compare attcompression.  That could, for example, cause relcache
reload to fail to adopt a new value following a change.

Michael Paquier and Tom Lane, per a gripe from Andres Freund.

Discussion: https://postgr.es/m/20210517204803.iyk5wwvwgtjcmc5w@alap3.anarazel.de

doc/src/sgml/catalogs.sgml

@@ -1236,6 +1236,15 @@
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>attalign</structfield> <type>char</type>
+      </para>
+      <para>
+       A copy of <literal>pg_type.typalign</literal> of this column's type
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>attstorage</structfield> <type>char</type>
@@ -1249,10 +1258,13 @@
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>attalign</structfield> <type>char</type>
+       <structfield>attcompression</structfield> <type>char</type>
       </para>
       <para>
-       A copy of <literal>pg_type.typalign</literal> of this column's type
+       The current compression method of the column.  If it is an invalid
+       compression method (<literal>'\0'</literal>) then column data will not
+       be compressed.  Otherwise, <literal>'p'</literal> = pglz compression or
+       <literal>'l'</literal> = <productname>LZ4</productname> compression.
       </para></entry>
      </row>
 
@@ -1355,18 +1367,6 @@
       </para></entry>
      </row>
 
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>attcompression</structfield> <type>char</type>
-      </para>
-      <para>
-       The current compression method of the column.  If it is an invalid
-       compression method (<literal>'\0'</literal>) then column data will not
-       be compressed.  Otherwise, <literal>'p'</literal> = pglz compression or
-       <literal>'l'</literal> = <productname>LZ4</productname> compression.
-      </para></entry>
-     </row>
-
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>attacl</structfield> <type>aclitem[]</type>

src/backend/access/common/tupdesc.c

@@ -424,7 +424,8 @@ equalTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2)
 		 * general it seems safer to check them always.
 		 *
 		 * attcacheoff must NOT be checked since it's possibly not set in both
-		 * copies.
+		 * copies.  We also intentionally ignore atthasmissing, since that's
+		 * not very relevant in tupdescs, which lack the attmissingval field.
 		 */
 		if (strcmp(NameStr(attr1->attname), NameStr(attr2->attname)) != 0)
 			return false;
@@ -440,9 +441,11 @@ equalTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2)
 			return false;
 		if (attr1->attbyval != attr2->attbyval)
 			return false;
+		if (attr1->attalign != attr2->attalign)
+			return false;
 		if (attr1->attstorage != attr2->attstorage)
 			return false;
-		if (attr1->attalign != attr2->attalign)
+		if (attr1->attcompression != attr2->attcompression)
 			return false;
 		if (attr1->attnotnull != attr2->attnotnull)
 			return false;
@@ -460,7 +463,7 @@ equalTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2)
 			return false;
 		if (attr1->attcollation != attr2->attcollation)
 			return false;
-		/* attacl, attoptions and attfdwoptions are not even present... */
+		/* variable-length fields are not even present... */
 	}
 
 	if (tupdesc1->constr != NULL)
@@ -639,12 +642,11 @@ TupleDescInitEntry(TupleDesc desc,
 	att->attbyval = typeForm->typbyval;
 	att->attalign = typeForm->typalign;
 	att->attstorage = typeForm->typstorage;
-	att->attcollation = typeForm->typcollation;
-
 	if (IsStorageCompressible(typeForm->typstorage))
 		att->attcompression = GetDefaultToastCompression();
 	else
 		att->attcompression = InvalidCompressionMethod;
+	att->attcollation = typeForm->typcollation;
 
 	ReleaseSysCache(tuple);
 }
@@ -709,6 +711,7 @@ TupleDescInitBuiltinEntry(TupleDesc desc,
 			att->attbyval = false;
 			att->attalign = TYPALIGN_INT;
 			att->attstorage = TYPSTORAGE_EXTENDED;
+			att->attcompression = GetDefaultToastCompression();
 			att->attcollation = DEFAULT_COLLATION_OID;
 			break;
 
@@ -717,6 +720,7 @@ TupleDescInitBuiltinEntry(TupleDesc desc,
 			att->attbyval = true;
 			att->attalign = TYPALIGN_CHAR;
 			att->attstorage = TYPSTORAGE_PLAIN;
+			att->attcompression = InvalidCompressionMethod;
 			att->attcollation = InvalidOid;
 			break;
 
@@ -725,6 +729,7 @@ TupleDescInitBuiltinEntry(TupleDesc desc,
 			att->attbyval = true;
 			att->attalign = TYPALIGN_INT;
 			att->attstorage = TYPSTORAGE_PLAIN;
+			att->attcompression = InvalidCompressionMethod;
 			att->attcollation = InvalidOid;
 			break;
 
@@ -733,6 +738,7 @@ TupleDescInitBuiltinEntry(TupleDesc desc,
 			att->attbyval = FLOAT8PASSBYVAL;
 			att->attalign = TYPALIGN_DOUBLE;
 			att->attstorage = TYPSTORAGE_PLAIN;
+			att->attcompression = InvalidCompressionMethod;
 			att->attcollation = InvalidOid;
 			break;
 

src/backend/access/spgist/spgutils.c

@@ -165,8 +165,8 @@ fillTypeDesc(SpGistTypeDesc *desc, Oid type)
 	typtup = (Form_pg_type) GETSTRUCT(tp);
 	desc->attlen = typtup->typlen;
 	desc->attbyval = typtup->typbyval;
-	desc->attstorage = typtup->typstorage;
 	desc->attalign = typtup->typalign;
+	desc->attstorage = typtup->typstorage;
 	ReleaseSysCache(tp);
 }
 
@@ -304,8 +304,8 @@ getSpGistTupleDesc(Relation index, SpGistTypeDesc *keyType)
 		att->attalign = keyType->attalign;
 		att->attstorage = keyType->attstorage;
 		/* We shouldn't need to bother with making these valid: */
-		att->attcollation = InvalidOid;
 		att->attcompression = InvalidCompressionMethod;
+		att->attcollation = InvalidOid;
 		/* In case we changed typlen, we'd better reset following offsets */
 		for (int i = spgFirstIncludeColumn; i < outTupDesc->natts; i++)
 			TupleDescAttr(outTupDesc, i)->attcacheoff = -1;

src/backend/bootstrap/bootstrap.c

@@ -699,8 +699,8 @@ DefineAttr(char *name, char *type, int attnum, int nullness)
 		attrtypes[attnum]->atttypid = Ap->am_oid;
 		attrtypes[attnum]->attlen = Ap->am_typ.typlen;
 		attrtypes[attnum]->attbyval = Ap->am_typ.typbyval;
-		attrtypes[attnum]->attstorage = Ap->am_typ.typstorage;
 		attrtypes[attnum]->attalign = Ap->am_typ.typalign;
+		attrtypes[attnum]->attstorage = Ap->am_typ.typstorage;
 		attrtypes[attnum]->attcollation = Ap->am_typ.typcollation;
 		/* if an array type, assume 1-dimensional attribute */
 		if (Ap->am_typ.typelem != InvalidOid && Ap->am_typ.typlen < 0)
@@ -713,8 +713,8 @@ DefineAttr(char *name, char *type, int attnum, int nullness)
 		attrtypes[attnum]->atttypid = TypInfo[typeoid].oid;
 		attrtypes[attnum]->attlen = TypInfo[typeoid].len;
 		attrtypes[attnum]->attbyval = TypInfo[typeoid].byval;
-		attrtypes[attnum]->attstorage = TypInfo[typeoid].storage;
 		attrtypes[attnum]->attalign = TypInfo[typeoid].align;
+		attrtypes[attnum]->attstorage = TypInfo[typeoid].storage;
 		attrtypes[attnum]->attcollation = TypInfo[typeoid].collation;
 		/* if an array type, assume 1-dimensional attribute */
 		if (TypInfo[typeoid].elem != InvalidOid &&
@@ -724,6 +724,11 @@ DefineAttr(char *name, char *type, int attnum, int nullness)
 			attrtypes[attnum]->attndims = 0;
 	}
 
+	if (IsStorageCompressible(attrtypes[attnum]->attstorage))
+		attrtypes[attnum]->attcompression = GetDefaultToastCompression();
+	else
+		attrtypes[attnum]->attcompression = InvalidCompressionMethod;
+
 	/*
 	 * If a system catalog column is collation-aware, force it to use C
 	 * collation, so that its behavior is independent of the database's
@@ -737,10 +742,6 @@ DefineAttr(char *name, char *type, int attnum, int nullness)
 	attrtypes[attnum]->attcacheoff = -1;
 	attrtypes[attnum]->atttypmod = -1;
 	attrtypes[attnum]->attislocal = true;
-	if (IsStorageCompressible(attrtypes[attnum]->attstorage))
-		attrtypes[attnum]->attcompression = GetDefaultToastCompression();
-	else
-		attrtypes[attnum]->attcompression = InvalidCompressionMethod;
 
 	if (nullness == BOOTCOL_NULL_FORCE_NOT_NULL)
 	{

src/backend/catalog/genbki.pl

@@ -897,8 +897,11 @@ sub morph_row_for_pgattr
 	$row->{atttypid}   = $type->{oid};
 	$row->{attlen}     = $type->{typlen};
 	$row->{attbyval}   = $type->{typbyval};
-	$row->{attstorage} = $type->{typstorage};
 	$row->{attalign}   = $type->{typalign};
+	$row->{attstorage} = $type->{typstorage};
+
+	$row->{attcompression} =
+	  $type->{typstorage} ne 'p' && $type->{typstorage} ne 'e' ? 'p' : '\0';
 
 	# set attndims if it's an array type
 	$row->{attndims} = $type->{typcategory} eq 'A' ? '1' : '0';
@@ -907,9 +910,6 @@ sub morph_row_for_pgattr
 	$row->{attcollation} =
 	  $type->{typcollation} ne '0' ? $C_COLLATION_OID : 0;
 
-	$row->{attcompression} =
-	  $type->{typstorage} ne 'p' && $type->{typstorage} ne 'e' ? 'p' : '\0';
-
 	if (defined $attr->{forcenotnull})
 	{
 		$row->{attnotnull} = 't';

src/backend/catalog/heap.c

@@ -146,7 +146,8 @@ static Node *cookConstraint(ParseState *pstate,
 /*
  * The initializers below do not include trailing variable length fields,
  * but that's OK - we're never going to reference anything beyond the
- * fixed-size portion of the structure anyway.
+ * fixed-size portion of the structure anyway.  Fields that can default
+ * to zeroes are also not mentioned.
  */
 
 static const FormData_pg_attribute a1 = {
@@ -157,8 +158,8 @@ static const FormData_pg_attribute a1 = {
 	.attcacheoff = -1,
 	.atttypmod = -1,
 	.attbyval = false,
-	.attstorage = TYPSTORAGE_PLAIN,
 	.attalign = TYPALIGN_SHORT,
+	.attstorage = TYPSTORAGE_PLAIN,
 	.attnotnull = true,
 	.attislocal = true,
 };
@@ -171,8 +172,8 @@ static const FormData_pg_attribute a2 = {
 	.attcacheoff = -1,
 	.atttypmod = -1,
 	.attbyval = true,
-	.attstorage = TYPSTORAGE_PLAIN,
 	.attalign = TYPALIGN_INT,
+	.attstorage = TYPSTORAGE_PLAIN,
 	.attnotnull = true,
 	.attislocal = true,
 };
@@ -185,8 +186,8 @@ static const FormData_pg_attribute a3 = {
 	.attcacheoff = -1,
 	.atttypmod = -1,
 	.attbyval = true,
-	.attstorage = TYPSTORAGE_PLAIN,
 	.attalign = TYPALIGN_INT,
+	.attstorage = TYPSTORAGE_PLAIN,
 	.attnotnull = true,
 	.attislocal = true,
 };
@@ -199,8 +200,8 @@ static const FormData_pg_attribute a4 = {
 	.attcacheoff = -1,
 	.atttypmod = -1,
 	.attbyval = true,
-	.attstorage = TYPSTORAGE_PLAIN,
 	.attalign = TYPALIGN_INT,
+	.attstorage = TYPSTORAGE_PLAIN,
 	.attnotnull = true,
 	.attislocal = true,
 };
@@ -213,8 +214,8 @@ static const FormData_pg_attribute a5 = {
 	.attcacheoff = -1,
 	.atttypmod = -1,
 	.attbyval = true,
-	.attstorage = TYPSTORAGE_PLAIN,
 	.attalign = TYPALIGN_INT,
+	.attstorage = TYPSTORAGE_PLAIN,
 	.attnotnull = true,
 	.attislocal = true,
 };
@@ -233,8 +234,8 @@ static const FormData_pg_attribute a6 = {
 	.attcacheoff = -1,
 	.atttypmod = -1,
 	.attbyval = true,
-	.attstorage = TYPSTORAGE_PLAIN,
 	.attalign = TYPALIGN_INT,
+	.attstorage = TYPSTORAGE_PLAIN,
 	.attnotnull = true,
 	.attislocal = true,
 };
@@ -779,8 +780,9 @@ InsertPgAttributeTuples(Relation pg_attribute_rel,
 		slot[slotCount]->tts_values[Anum_pg_attribute_attcacheoff - 1] = Int32GetDatum(-1);
 		slot[slotCount]->tts_values[Anum_pg_attribute_atttypmod - 1] = Int32GetDatum(attrs->atttypmod);
 		slot[slotCount]->tts_values[Anum_pg_attribute_attbyval - 1] = BoolGetDatum(attrs->attbyval);
-		slot[slotCount]->tts_values[Anum_pg_attribute_attstorage - 1] = CharGetDatum(attrs->attstorage);
 		slot[slotCount]->tts_values[Anum_pg_attribute_attalign - 1] = CharGetDatum(attrs->attalign);
+		slot[slotCount]->tts_values[Anum_pg_attribute_attstorage - 1] = CharGetDatum(attrs->attstorage);
+		slot[slotCount]->tts_values[Anum_pg_attribute_attcompression - 1] = CharGetDatum(attrs->attcompression);
 		slot[slotCount]->tts_values[Anum_pg_attribute_attnotnull - 1] = BoolGetDatum(attrs->attnotnull);
 		slot[slotCount]->tts_values[Anum_pg_attribute_atthasdef - 1] = BoolGetDatum(attrs->atthasdef);
 		slot[slotCount]->tts_values[Anum_pg_attribute_atthasmissing - 1] = BoolGetDatum(attrs->atthasmissing);
@@ -790,7 +792,6 @@ InsertPgAttributeTuples(Relation pg_attribute_rel,
 		slot[slotCount]->tts_values[Anum_pg_attribute_attislocal - 1] = BoolGetDatum(attrs->attislocal);
 		slot[slotCount]->tts_values[Anum_pg_attribute_attinhcount - 1] = Int32GetDatum(attrs->attinhcount);
 		slot[slotCount]->tts_values[Anum_pg_attribute_attcollation - 1] = ObjectIdGetDatum(attrs->attcollation);
-		slot[slotCount]->tts_values[Anum_pg_attribute_attcompression - 1] = CharGetDatum(attrs->attcompression);
 		if (attoptions && attoptions[natts] != (Datum) 0)
 			slot[slotCount]->tts_values[Anum_pg_attribute_attoptions - 1] = attoptions[natts];
 		else

src/backend/catalog/index.c

@@ -345,8 +345,8 @@ ConstructTupleDescriptor(Relation heapRelation,
 			to->attndims = from->attndims;
 			to->atttypmod = from->atttypmod;
 			to->attbyval = from->attbyval;
-			to->attstorage = from->attstorage;
 			to->attalign = from->attalign;
+			to->attstorage = from->attstorage;
 			to->attcompression = from->attcompression;
 		}
 		else
@@ -373,16 +373,16 @@ ConstructTupleDescriptor(Relation heapRelation,
 			 */
 			to->atttypid = keyType;
 			to->attlen = typeTup->typlen;
+			to->atttypmod = exprTypmod(indexkey);
 			to->attbyval = typeTup->typbyval;
-			to->attstorage = typeTup->typstorage;
 			to->attalign = typeTup->typalign;
-			to->atttypmod = exprTypmod(indexkey);
+			to->attstorage = typeTup->typstorage;
 
 			/*
 			 * For expression columns, set attcompression invalid, since
 			 * there's no table column from which to copy the value. Whenever
 			 * we actually need to compress a value, we'll use whatever the
-			 * current value of default_compression_method is at that point in
+			 * current value of default_toast_compression is at that point in
 			 * time.
 			 */
 			to->attcompression = InvalidCompressionMethod;
@@ -464,6 +464,8 @@ ConstructTupleDescriptor(Relation heapRelation,
 			to->attbyval = typeTup->typbyval;
 			to->attalign = typeTup->typalign;
 			to->attstorage = typeTup->typstorage;
+			/* As above, use the default compression method in this case */
+			to->attcompression = InvalidCompressionMethod;
 
 			ReleaseSysCache(tuple);
 		}

src/backend/commands/tablecmds.c

@@ -2640,8 +2640,8 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 				def->constraints = NIL;
 				def->location = -1;
 				if (CompressionMethodIsValid(attribute->attcompression))
-					def->compression = pstrdup(GetCompressionMethodName(
-																		attribute->attcompression));
+					def->compression =
+						pstrdup(GetCompressionMethodName(attribute->attcompression));
 				else
 					def->compression = NULL;
 				inhSchema = lappend(inhSchema, def);
@@ -6596,12 +6596,19 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	attribute.atttypid = typeOid;
 	attribute.attstattarget = (newattnum > 0) ? -1 : 0;
 	attribute.attlen = tform->typlen;
-	attribute.atttypmod = typmod;
 	attribute.attnum = newattnum;
-	attribute.attbyval = tform->typbyval;
 	attribute.attndims = list_length(colDef->typeName->arrayBounds);
-	attribute.attstorage = tform->typstorage;
+	attribute.atttypmod = typmod;
+	attribute.attbyval = tform->typbyval;
 	attribute.attalign = tform->typalign;
+	attribute.attstorage = tform->typstorage;
+	/* do not set compression in views etc */
+	if (rel->rd_rel->relkind == RELKIND_RELATION ||
+		rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+		attribute.attcompression = GetAttributeCompression(&attribute,
+														   colDef->compression);
+	else
+		attribute.attcompression = InvalidCompressionMethod;
 	attribute.attnotnull = colDef->is_not_null;
 	attribute.atthasdef = false;
 	attribute.atthasmissing = false;
@@ -6612,17 +6619,6 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	attribute.attinhcount = colDef->inhcount;
 	attribute.attcollation = collOid;
 
-	/*
-	 * lookup attribute's compression method and store it in the
-	 * attr->attcompression.
-	 */
-	if (rel->rd_rel->relkind == RELKIND_RELATION ||
-		rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
-		attribute.attcompression = GetAttributeCompression(&attribute,
-														   colDef->compression);
-	else
-		attribute.attcompression = InvalidCompressionMethod;
-
 	/* attribute.attacl is handled by InsertPgAttributeTuples() */
 
 	ReleaseSysCache(typeTuple);

src/include/access/spgist_private.h

@@ -137,8 +137,8 @@ typedef struct SpGistTypeDesc
 	Oid			type;
 	int16		attlen;
 	bool		attbyval;
-	char		attstorage;
 	char		attalign;
+	char		attstorage;
 } SpGistTypeDesc;
 
 typedef struct SpGistState

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202105121
+#define CATALOG_VERSION_NO	202105231
 
 #endif

src/include/catalog/pg_attribute.h

@@ -111,6 +111,12 @@ CATALOG(pg_attribute,1249,AttributeRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(75,
 	 */
 	bool		attbyval;
 
+	/*
+	 * attalign is a copy of the typalign field from pg_type for this
+	 * attribute.  See atttypid comments above.
+	 */
+	char		attalign;
+
 	/*----------
 	 * attstorage tells for VARLENA attributes, what the heap access
 	 * methods can do to it if a given tuple doesn't fit into a page.
@@ -120,10 +126,10 @@ CATALOG(pg_attribute,1249,AttributeRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(75,
 	char		attstorage;
 
 	/*
-	 * attalign is a copy of the typalign field from pg_type for this
-	 * attribute.  See atttypid comments above.
+	 * Compression method.  Must be InvalidCompressionMethod if and only if
+	 * typstorage is 'plain' or 'external'.
 	 */
-	char		attalign;
+	char		attcompression BKI_DEFAULT('\0');
 
 	/* This flag represents the "NOT NULL" constraint */
 	bool		attnotnull;
@@ -160,12 +166,6 @@ CATALOG(pg_attribute,1249,AttributeRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(75,
 	/* attribute's collation, if any */
 	Oid			attcollation BKI_LOOKUP_OPT(pg_collation);
 
-	/*
-	 * compression method.  Must be InvalidCompressionMethod if and only if
-	 * typstorage is 'plain' or 'external'.
-	 */
-	char		attcompression BKI_DEFAULT('\0');
-
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
 	/* NOTE: The following fields are not present in tuple descriptors. */
 
@@ -190,10 +190,10 @@ CATALOG(pg_attribute,1249,AttributeRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(75,
  * ATTRIBUTE_FIXED_PART_SIZE is the size of the fixed-layout,
  * guaranteed-not-null part of a pg_attribute row.  This is in fact as much
  * of the row as gets copied into tuple descriptors, so don't expect you
- * can access fields beyond attcollation except in a real tuple!
+ * can access the variable-length fields except in a real tuple!
  */
 #define ATTRIBUTE_FIXED_PART_SIZE \
-	(offsetof(FormData_pg_attribute,attcompression) + sizeof(char))
+	(offsetof(FormData_pg_attribute,attcollation) + sizeof(Oid))
 
 /* ----------------
  *		Form_pg_attribute corresponds to a pointer to a tuple with