Make various variables const (read-only).

These changes should generally improve correctness/maintainability.
A nice side benefit is that several kilobytes move from initialized
data to text segment, allowing them to be shared across processes and
probably reducing copy-on-write overhead while forking a new backend.
Unfortunately this doesn't seem to help libpq in the same way (at least
not when it's compiled with -fpic on x86_64), but we can hope the linker
at least collects all nominally-const data together even if it's not
actually part of the text segment.

Also, make pg_encname_tbl[] static in encnames.c, since there seems
no very good reason for any other code to use it; per a suggestion
from Wim Lewis, who independently submitted a patch that was mostly
a subset of this one.

Oskari Saarenmaa, with some editorialization by me

Author: tglsfdc

src/backend/catalog/objectaddress.c

@@ -101,7 +101,7 @@ typedef struct
 										 * class? */
 } ObjectPropertyType;
 
-static ObjectPropertyType ObjectProperty[] =
+static const ObjectPropertyType ObjectProperty[] =
 {
 	{
 		CastRelationId,
@@ -431,7 +431,7 @@ static ObjectAddress get_object_address_type(ObjectType objtype,
 						List *objname, bool missing_ok);
 static ObjectAddress get_object_address_opcf(ObjectType objtype, List *objname,
 						List *objargs, bool missing_ok);
-static ObjectPropertyType *get_object_property_data(Oid class_id);
+static const ObjectPropertyType *get_object_property_data(Oid class_id);
 
 static void getRelationDescription(StringInfo buffer, Oid relid);
 static void getOpFamilyDescription(StringInfo buffer, Oid opfid);
@@ -1297,7 +1297,7 @@ get_object_namespace(const ObjectAddress *address)
 	HeapTuple	tuple;
 	bool		isnull;
 	Oid			oid;
-	ObjectPropertyType *property;
+	const ObjectPropertyType *property;
 
 	/* If not owned by a namespace, just return InvalidOid. */
 	property = get_object_property_data(address->classId);
@@ -1329,71 +1329,71 @@ get_object_namespace(const ObjectAddress *address)
 Oid
 get_object_oid_index(Oid class_id)
 {
-	ObjectPropertyType *prop = get_object_property_data(class_id);
+	const ObjectPropertyType *prop = get_object_property_data(class_id);
 
 	return prop->oid_index_oid;
 }
 
 int
 get_object_catcache_oid(Oid class_id)
 {
-	ObjectPropertyType *prop = get_object_property_data(class_id);
+	const ObjectPropertyType *prop = get_object_property_data(class_id);
 
 	return prop->oid_catcache_id;
 }
 
 int
 get_object_catcache_name(Oid class_id)
 {
-	ObjectPropertyType *prop = get_object_property_data(class_id);
+	const ObjectPropertyType *prop = get_object_property_data(class_id);
 
 	return prop->name_catcache_id;
 }
 
 AttrNumber
 get_object_attnum_name(Oid class_id)
 {
-	ObjectPropertyType *prop = get_object_property_data(class_id);
+	const ObjectPropertyType *prop = get_object_property_data(class_id);
 
 	return prop->attnum_name;
 }
 
 AttrNumber
 get_object_attnum_namespace(Oid class_id)
 {
-	ObjectPropertyType *prop = get_object_property_data(class_id);
+	const ObjectPropertyType *prop = get_object_property_data(class_id);
 
 	return prop->attnum_namespace;
 }
 
 AttrNumber
 get_object_attnum_owner(Oid class_id)
 {
-	ObjectPropertyType *prop = get_object_property_data(class_id);
+	const ObjectPropertyType *prop = get_object_property_data(class_id);
 
 	return prop->attnum_owner;
 }
 
 AttrNumber
 get_object_attnum_acl(Oid class_id)
 {
-	ObjectPropertyType *prop = get_object_property_data(class_id);
+	const ObjectPropertyType *prop = get_object_property_data(class_id);
 
 	return prop->attnum_acl;
 }
 
 AclObjectKind
 get_object_aclkind(Oid class_id)
 {
-	ObjectPropertyType *prop = get_object_property_data(class_id);
+	const ObjectPropertyType *prop = get_object_property_data(class_id);
 
 	return prop->acl_kind;
 }
 
 bool
 get_object_namensp_unique(Oid class_id)
 {
-	ObjectPropertyType *prop = get_object_property_data(class_id);
+	const ObjectPropertyType *prop = get_object_property_data(class_id);
 
 	return prop->is_nsp_name_unique;
 }
@@ -1419,10 +1419,10 @@ is_objectclass_supported(Oid class_id)
 /*
  * Find ObjectProperty structure by class_id.
  */
-static ObjectPropertyType *
+static const ObjectPropertyType *
 get_object_property_data(Oid class_id)
 {
-	static ObjectPropertyType *prop_last = NULL;
+	static const ObjectPropertyType *prop_last = NULL;
 	int			index;
 
 	/*

src/backend/commands/conversioncmds.c

@@ -46,7 +46,7 @@ CreateConversionCommand(CreateConversionStmt *stmt)
 	const char *from_encoding_name = stmt->for_encoding_name;
 	const char *to_encoding_name = stmt->to_encoding_name;
 	List	   *func_name = stmt->func_name;
-	static Oid	funcargs[] = {INT4OID, INT4OID, CSTRINGOID, INTERNALOID, INT4OID};
+	static const Oid funcargs[] = {INT4OID, INT4OID, CSTRINGOID, INTERNALOID, INT4OID};
 	char		result[1];
 
 	/* Convert list of names to a name and namespace */

src/backend/regex/regc_lex.c

@@ -716,10 +716,10 @@ static int						/* not actually used, but convenient for RETV */
 lexescape(struct vars * v)
 {
 	chr			c;
-	static chr	alert[] = {
+	static const chr alert[] = {
 		CHR('a'), CHR('l'), CHR('e'), CHR('r'), CHR('t')
 	};
-	static chr	esc[] = {
+	static const chr esc[] = {
 		CHR('E'), CHR('S'), CHR('C')
 	};
 	const chr  *save;

src/backend/regex/regcomp.c

@@ -274,7 +274,7 @@ struct vars
 
 
 /* static function list */
-static struct fns functions = {
+static const struct fns functions = {
 	rfree,						/* regfree insides */
 };
 

src/backend/regex/regerror.c

@@ -34,10 +34,10 @@
 #include "regex/regguts.h"
 
 /* unknown-error explanation */
-static char unk[] = "*** unknown regex error code 0x%x ***";
+static const char unk[] = "*** unknown regex error code 0x%x ***";
 
 /* struct to map among codes, code names, and explanations */
-static struct rerr
+static const struct rerr
 {
 	int			code;
 	const char *name;
@@ -62,7 +62,7 @@ pg_regerror(int errcode,		/* error code, or REG_ATOI or REG_ITOA */
 			char *errbuf,		/* result buffer (unless errbuf_size==0) */
 			size_t errbuf_size) /* available space in errbuf, can be 0 */
 {
-	struct rerr *r;
+	const struct rerr *r;
 	const char *msg;
 	char		convbuf[sizeof(unk) + 50];		/* 50 = plenty for int */
 	size_t		len;

src/backend/tsearch/wparser_def.c

@@ -789,7 +789,7 @@ p_isspecial(TParser *prs)
 	 */
 	if (GetDatabaseEncoding() == PG_UTF8 && prs->usewide)
 	{
-		static pg_wchar strange_letter[] = {
+		static const pg_wchar strange_letter[] = {
 			/*
 			 * use binary search, so elements should be ordered
 			 */
@@ -1023,7 +1023,7 @@ p_isspecial(TParser *prs)
 			0xAA34,				/* CHAM CONSONANT SIGN RA */
 			0xAA4D				/* CHAM CONSONANT SIGN FINAL H */
 		};
-		pg_wchar   *StopLow = strange_letter,
+		const pg_wchar *StopLow = strange_letter,
 				   *StopHigh = strange_letter + lengthof(strange_letter),
 				   *StopMiddle;
 		pg_wchar	c;

src/backend/utils/adt/datetime.c

@@ -59,10 +59,10 @@ const int	day_tab[2][13] =
 	{31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31, 0}
 };
 
-char	   *months[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
+const char *const months[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
 "Jul", "Aug", "Sep", "Oct", "Nov", "Dec", NULL};
 
-char	   *days[] = {"Sunday", "Monday", "Tuesday", "Wednesday",
+const char *const days[] = {"Sunday", "Monday", "Tuesday", "Wednesday",
 "Thursday", "Friday", "Saturday", NULL};
 
 
@@ -186,7 +186,7 @@ static const datetkn datetktbl[] = {
 
 static int	szdatetktbl = sizeof datetktbl / sizeof datetktbl[0];
 
-static datetkn deltatktbl[] = {
+static const datetkn deltatktbl[] = {
 	/* text, token, lexval */
 	{"@", IGNORE_DTF, 0},		/* postgres relative prefix */
 	{DAGO, AGO, 0},				/* "ago" indicates negative time offset */