Reorder subskiplsn in pg_subscription to avoid alignment issues.

The column 'subskiplsn' uses TYPALIGN_DOUBLE (which has 4 bytes alignment
on AIX) for storage. But the C Struct (Form_pg_subscription) has 8-byte
alignment for this field, so retrieving it from storage causes an
unaligned read.

To fix this, we rearranged the 'subskiplsn' column in the catalog so that
it naturally comes at an 8-byte boundary.

We have fixed a similar problem in commit f3b421d. This patch adds a
test to avoid a similar mistake in the future.

Reported-by: Noah Misch
Diagnosed-by: Noah Misch, Masahiko Sawada, Amit Kapila
Author: Masahiko Sawada
Reviewed-by: Noah Misch, Amit Kapila
Discussion: https://postgr.es/m/[email protected]
	    https://postgr.es/m/CAD21AoDeScrsHhLyEPYqN3sydg6PxAPVBboK=30xJfUVihNZDA@mail.gmail.com

Author: Amit Kapila

doc/src/sgml/catalogs.sgml

@@ -7823,6 +7823,16 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>subskiplsn</structfield> <type>pg_lsn</type>
+      </para>
+      <para>
+       Finish LSN of the transaction whose changes are to be skipped, if a valid
+       LSN; otherwise <literal>0/0</literal>.
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>subname</structfield> <type>name</type>
@@ -7893,16 +7903,6 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       </para></entry>
      </row>
 
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>subskiplsn</structfield> <type>pg_lsn</type>
-      </para>
-      <para>
-       Finish LSN of the transaction whose changes are to be skipped, if a valid
-       LSN; otherwise <literal>0/0</literal>.
-      </para></entry>
-     </row>
-
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>subconninfo</structfield> <type>text</type>

src/backend/catalog/pg_subscription.c

@@ -63,14 +63,14 @@ GetSubscription(Oid subid, bool missing_ok)
 	sub = (Subscription *) palloc(sizeof(Subscription));
 	sub->oid = subid;
 	sub->dbid = subform->subdbid;
+	sub->skiplsn = subform->subskiplsn;
 	sub->name = pstrdup(NameStr(subform->subname));
 	sub->owner = subform->subowner;
 	sub->enabled = subform->subenabled;
 	sub->binary = subform->subbinary;
 	sub->stream = subform->substream;
 	sub->twophasestate = subform->subtwophasestate;
 	sub->disableonerr = subform->subdisableonerr;
-	sub->skiplsn = subform->subskiplsn;
 
 	/* Get conninfo */
 	datum = SysCacheGetAttr(SUBSCRIPTIONOID,

src/backend/catalog/system_views.sql

@@ -1285,8 +1285,8 @@ REVOKE ALL ON pg_replication_origin_status FROM public;
 
 -- All columns of pg_subscription except subconninfo are publicly readable.
 REVOKE ALL ON pg_subscription FROM public;
-GRANT SELECT (oid, subdbid, subname, subowner, subenabled, subbinary,
-              substream, subtwophasestate, subdisableonerr, subskiplsn, subslotname,
+GRANT SELECT (oid, subdbid, subskiplsn, subname, subowner, subenabled,
+              subbinary, substream, subtwophasestate, subdisableonerr, subslotname,
               subsynccommit, subpublications)
     ON pg_subscription TO public;
 

src/backend/commands/subscriptioncmds.c

@@ -596,6 +596,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 							   Anum_pg_subscription_oid);
 	values[Anum_pg_subscription_oid - 1] = ObjectIdGetDatum(subid);
 	values[Anum_pg_subscription_subdbid - 1] = ObjectIdGetDatum(MyDatabaseId);
+	values[Anum_pg_subscription_subskiplsn - 1] = LSNGetDatum(InvalidXLogRecPtr);
 	values[Anum_pg_subscription_subname - 1] =
 		DirectFunctionCall1(namein, CStringGetDatum(stmt->subname));
 	values[Anum_pg_subscription_subowner - 1] = ObjectIdGetDatum(owner);
@@ -607,7 +608,6 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 					 LOGICALREP_TWOPHASE_STATE_PENDING :
 					 LOGICALREP_TWOPHASE_STATE_DISABLED);
 	values[Anum_pg_subscription_subdisableonerr - 1] = BoolGetDatum(opts.disableonerr);
-	values[Anum_pg_subscription_subskiplsn - 1] = LSNGetDatum(InvalidXLogRecPtr);
 	values[Anum_pg_subscription_subconninfo - 1] =
 		CStringGetTextDatum(conninfo);
 	if (opts.slot_name)

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202204062
+#define CATALOG_VERSION_NO	202204071
 
 #endif

src/include/catalog/pg_subscription.h

@@ -54,6 +54,10 @@ CATALOG(pg_subscription,6100,SubscriptionRelationId) BKI_SHARED_RELATION BKI_ROW
 
 	Oid			subdbid BKI_LOOKUP(pg_database);	/* Database the
 													 * subscription is in. */
+
+	XLogRecPtr	subskiplsn;		/* All changes finished at this LSN are
+								 * skipped */
+
 	NameData	subname;		/* Name of the subscription */
 
 	Oid			subowner BKI_LOOKUP(pg_authid); /* Owner of the subscription */
@@ -71,9 +75,6 @@ CATALOG(pg_subscription,6100,SubscriptionRelationId) BKI_SHARED_RELATION BKI_ROW
 	bool		subdisableonerr;	/* True if a worker error should cause the
 									 * subscription to be disabled */
 
-	XLogRecPtr	subskiplsn;		/* All changes finished at this LSN are
-								 * skipped */
-
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
 	/* Connection string to the publisher */
 	text		subconninfo BKI_FORCE_NOT_NULL;
@@ -103,6 +104,8 @@ typedef struct Subscription
 	Oid			oid;			/* Oid of the subscription */
 	Oid			dbid;			/* Oid of the database which subscription is
 								 * in */
+	XLogRecPtr	skiplsn;		/* All changes finished at this LSN are
+								 * skipped */
 	char	   *name;			/* Name of the subscription */
 	Oid			owner;			/* Oid of the subscription owner */
 	bool		enabled;		/* Indicates if the subscription is enabled */
@@ -113,8 +116,6 @@ typedef struct Subscription
 	bool		disableonerr;	/* Indicates if the subscription should be
 								 * automatically disabled if a worker error
 								 * occurs */
-	XLogRecPtr	skiplsn;		/* All changes finished at this LSN are
-								 * skipped */
 	char	   *conninfo;		/* Connection string to the publisher */
 	char	   *slotname;		/* Name of the replication slot */
 	char	   *synccommit;		/* Synchronous commit setting for worker */

src/test/regress/expected/sanity_check.out

@@ -25,3 +25,32 @@ SELECT relname, relkind
 ---------+---------
 (0 rows)
 
+--
+-- When ALIGNOF_DOUBLE==4 (e.g. AIX), the C ABI may impose 8-byte alignment on
+-- some of the C types that correspond to TYPALIGN_DOUBLE SQL types.  To ensure
+-- catalog C struct layout matches catalog tuple layout, arrange for the tuple
+-- offset of each fixed-width, attalign='d' catalog column to be divisible by 8
+-- unconditionally.  Keep such columns before the first NameData column of the
+-- catalog, since packagers can override NAMEDATALEN to an odd number.
+--
+WITH check_columns AS (
+ SELECT relname, attname,
+  array(
+   SELECT t.oid
+    FROM pg_type t JOIN pg_attribute pa ON t.oid = pa.atttypid
+    WHERE pa.attrelid = a.attrelid AND
+          pa.attnum > 0 AND pa.attnum <= a.attnum
+    ORDER BY pa.attnum) AS coltypes
+ FROM pg_attribute a JOIN pg_class c ON c.oid = attrelid
+  JOIN pg_namespace n ON c.relnamespace = n.oid
+ WHERE attalign = 'd' AND relkind = 'r' AND
+  attnotnull AND attlen <> -1 AND n.nspname = 'pg_catalog'
+)
+SELECT relname, attname, coltypes, get_column_offset(coltypes)
+ FROM check_columns
+ WHERE get_column_offset(coltypes) % 8 != 0 OR
+       'name'::regtype::oid = ANY(coltypes);
+ relname | attname | coltypes | get_column_offset 
+---------+---------+----------+-------------------
+(0 rows)
+

src/test/regress/expected/test_setup.out

@@ -206,6 +206,10 @@ CREATE FUNCTION ttdummy ()
     RETURNS trigger
     AS :'regresslib'
     LANGUAGE C;
+CREATE FUNCTION get_column_offset (oid[])
+    RETURNS int
+    AS :'regresslib'
+    LANGUAGE C STRICT STABLE PARALLEL SAFE;
 -- Use hand-rolled hash functions and operator classes to get predictable
 -- result on different machines.  The hash function for int4 simply returns
 -- the sum of the values passed to it and the one for text returns the length

src/test/regress/regress.c

@@ -41,6 +41,7 @@
 #include "storage/spin.h"
 #include "utils/builtins.h"
 #include "utils/geo_decls.h"
+#include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
 #include "utils/typcache.h"
@@ -1216,3 +1217,47 @@ binary_coercible(PG_FUNCTION_ARGS)
 
 	PG_RETURN_BOOL(IsBinaryCoercible(srctype, targettype));
 }
+
+/*
+ * Return the column offset of the last data in the given array of
+ * data types.  The input data types must be fixed-length data types.
+ */
+PG_FUNCTION_INFO_V1(get_column_offset);
+Datum
+get_column_offset(PG_FUNCTION_ARGS)
+{
+	ArrayType	*ta = PG_GETARG_ARRAYTYPE_P(0);
+	Oid			*type_oids;
+	int			ntypes;
+	int			column_offset = 0;
+
+	if (ARR_HASNULL(ta) && array_contains_nulls(ta))
+		elog(ERROR, "argument must not contain nulls");
+
+	if (ARR_NDIM(ta) > 1)
+		elog(ERROR, "argument must be empty or one-dimensional array");
+
+	type_oids = (Oid *) ARR_DATA_PTR(ta);
+	ntypes = ArrayGetNItems(ARR_NDIM(ta), ARR_DIMS(ta));
+	for (int i = 0; i < ntypes; i++)
+	{
+		Oid typeoid = type_oids[i];
+		int16		typlen;
+		bool		typbyval;
+		char		typalign;
+
+		get_typlenbyvalalign(typeoid, &typlen, &typbyval, &typalign);
+
+		/* the data type must be fixed-length */
+		if (!(typbyval || (typlen > 0)))
+			elog(ERROR, "type %u is not fixed-length data type", typeoid);
+
+		column_offset = att_align_nominal(column_offset, typalign);
+
+		/* not include the last type size */
+		if (i != (ntypes - 1))
+			column_offset += typlen;
+	}
+
+	PG_RETURN_INT32(column_offset);
+}

src/test/regress/sql/sanity_check.sql

@@ -19,3 +19,29 @@ SELECT relname, relkind
   FROM pg_class
  WHERE relkind IN ('v', 'c', 'f', 'p', 'I')
        AND relfilenode <> 0;
+
+--
+-- When ALIGNOF_DOUBLE==4 (e.g. AIX), the C ABI may impose 8-byte alignment on
+-- some of the C types that correspond to TYPALIGN_DOUBLE SQL types.  To ensure
+-- catalog C struct layout matches catalog tuple layout, arrange for the tuple
+-- offset of each fixed-width, attalign='d' catalog column to be divisible by 8
+-- unconditionally.  Keep such columns before the first NameData column of the
+-- catalog, since packagers can override NAMEDATALEN to an odd number.
+--
+WITH check_columns AS (
+ SELECT relname, attname,
+  array(
+   SELECT t.oid
+    FROM pg_type t JOIN pg_attribute pa ON t.oid = pa.atttypid
+    WHERE pa.attrelid = a.attrelid AND
+          pa.attnum > 0 AND pa.attnum <= a.attnum
+    ORDER BY pa.attnum) AS coltypes
+ FROM pg_attribute a JOIN pg_class c ON c.oid = attrelid
+  JOIN pg_namespace n ON c.relnamespace = n.oid
+ WHERE attalign = 'd' AND relkind = 'r' AND
+  attnotnull AND attlen <> -1 AND n.nspname = 'pg_catalog'
+)
+SELECT relname, attname, coltypes, get_column_offset(coltypes)
+ FROM check_columns
+ WHERE get_column_offset(coltypes) % 8 != 0 OR
+       'name'::regtype::oid = ANY(coltypes);

src/test/regress/sql/test_setup.sql

@@ -253,6 +253,11 @@ CREATE FUNCTION ttdummy ()
     AS :'regresslib'
     LANGUAGE C;
 
+CREATE FUNCTION get_column_offset (oid[])
+    RETURNS int
+    AS :'regresslib'
+    LANGUAGE C STRICT STABLE PARALLEL SAFE;
+
 -- Use hand-rolled hash functions and operator classes to get predictable
 -- result on different machines.  The hash function for int4 simply returns
 -- the sum of the values passed to it and the one for text returns the length