Cleanup the contrib/lo module: there is no need anymore to implement

a physically separate type.  Defining 'lo' as a domain over OID works
just fine and is more efficient.  Improve documentation and fix up the
test script.  (Would like to turn test script into a proper regression
test, but right now its output is not constant because of numeric OIDs;
plus it makes Unix-specific assumptions about files it can import.)

Author: tglsfdc

contrib/lo/README.lo

@@ -8,62 +8,81 @@ also), is that the specification assumes that references to BLOBS (Binary
 Large OBjectS) are stored within a table, and if that entry is changed, the
 associated BLOB is deleted from the database.
 
-As PostgreSQL stands, this doesn't occur. It allocates an OID for each object,
-and it is up to the application to store, and ultimately delete the objects.
-
-Now this is fine for new postgresql specific applications, but existing ones
-using JDBC or ODBC wont delete the objects, arising to orphaning - objects
+As PostgreSQL stands, this doesn't occur.  Large objects are treated as
+objects in their own right; a table entry can reference a large object by
+OID, but there can be multiple table entries referencing the same large
+object OID, so the system doesn't delete the large object just because you
+change or remove one such entry.
+
+Now this is fine for new PostgreSQL-specific applications, but existing ones
+using JDBC or ODBC won't delete the objects, resulting in orphaning - objects
 that are not referenced by anything, and simply occupy disk space.
 
+
 The Fix
 
 I've fixed this by creating a new data type 'lo', some support functions, and
-a Trigger which handles the orphaning problem.
+a Trigger which handles the orphaning problem.  The trigger essentially just
+does a 'lo_unlink' whenever you delete or modify a value referencing a large
+object.  When you use this trigger, you are assuming that there is only one
+database reference to any large object that is referenced in a
+trigger-controlled column!
+
+The 'lo' type was created because we needed to differentiate between plain
+OIDs and Large Objects. Currently the JDBC driver handles this dilemma easily,
+but (after talking to Byron), the ODBC driver needed a unique type. They had
+created an 'lo' type, but not the solution to orphaning.
+
+You don't actually have to use the 'lo' type to use the trigger, but it may be
+convenient to use it to keep track of which columns in your database represent
+large objects that you are managing with the trigger.
 
-The 'lo' type was created because we needed to differenciate between normal
-Oid's and Large Objects. Currently the JDBC driver handles this dilema easily,
-but (after talking to Byron), the ODBC driver needed a unique type. They had created an 'lo' type, but not the solution to orphaning.
 
 Install
 
 Ok, first build the shared library, and install. Typing 'make install' in the
 contrib/lo directory should do it.
 
-Then, as the postgres super user, run the lo.sql script. This will install the
-type, and define the support functions.
+Then, as the postgres super user, run the lo.sql script in any database that
+needs the features. This will install the type, and define the support
+functions.  You can run the script once in template1, and the objects will be
+inherited by subsequently-created databases.
+
 
 How to Use
 
 The easiest way is by an example:
 
-> create table image (title text,raster lo);
-> create trigger t_image before update or delete on image for each row execute procedure lo_manage(raster);
+> create table image (title text, raster lo);
+> create trigger t_raster before update or delete on image
+>   for each row execute procedure lo_manage(raster);
 
-Here, a trigger is created for each column that contains a lo type.
+Create a trigger for each column that contains a lo type, and give the column
+name as the trigger procedure argument.  You can have more than one trigger on
+a table if you need multiple lo columns in the same table, but don't forget to
+give a different name to each trigger.
 
-Issues
 
-* dropping a table will still orphan any objects it contains, as the trigger
-  is not actioned.
+Issues
 
-  For now, precede the 'drop table' with 'delete from {table}'. However, this
-  could be fixed by having 'drop table' perform an additional
+* Dropping a table will still orphan any objects it contains, as the trigger
+  is not executed.
 
-      'select lo_unlink({colname}::oid) from {tablename}'
+  Avoid this by preceding the 'drop table' with 'delete from {table}'.
 
-  for each column, before actually dropping the table.
+  If you already have, or suspect you have, orphaned large objects, see
+  the contrib/vacuumlo module to help you clean them up.  It's a good idea
+  to run contrib/vacuumlo occasionally as a back-stop to the lo_manage
+  trigger.
 
 * Some frontends may create their own tables, and will not create the
   associated trigger(s). Also, users may not remember (or know) to create
   the triggers.
 
-  This can be solved, but would involve changes to the parser.
-
 As the ODBC driver needs a permanent lo type (& JDBC could be optimised to
 use it if it's Oid is fixed), and as the above issues can only be fixed by
 some internal changes, I feel it should become a permanent built-in type.
 
 I'm releasing this into contrib, just to get it out, and tested.
 
 Peter Mount <peter@retep.org.uk> June 13 1998
-

contrib/lo/lo.c

@@ -1,7 +1,7 @@
 /*
- *	PostgreSQL type definitions for managed LargeObjects.
+ *	PostgreSQL definitions for managed Large Objects.
  *
- *	$PostgreSQL: pgsql/contrib/lo/lo.c,v 1.14 2003/11/29 19:51:35 pgsql Exp $
+ *	$PostgreSQL: pgsql/contrib/lo/lo.c,v 1.15 2005/06/23 00:06:37 tgl Exp $
  *
  */
 
@@ -21,117 +21,12 @@
 #define atooid(x)  ((Oid) strtoul((x), NULL, 10))
 
 
-/*
- *	This is the internal storage format for managed large objects
- *
- */
-
-typedef Oid Blob;
-
-/*
- *	Various forward declarations:
- */
-
-Blob	   *lo_in(char *str);	/* Create from String		*/
-char	   *lo_out(Blob * addr);	/* Output oid as String		*/
-Oid			lo_oid(Blob * addr);	/* Return oid as an oid		*/
-Blob	   *lo(Oid oid);		/* Return Blob based on oid */
-Datum		lo_manage(PG_FUNCTION_ARGS);		/* Trigger handler		   */
-
-/*
- * This creates a large object, and sets its OID to the value in the
- * supplied string.
- *
- * If the string is empty, then a new LargeObject is created, and its oid
- * is placed in the resulting lo.
- */
-Blob *
-lo_in(char *str)
-{
-	Blob	   *result;
-	Oid			oid;
-	int			count;
-
-	if (strlen(str) > 0)
-	{
-		count = sscanf(str, "%u", &oid);
-
-		if (count < 1)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("error in parsing \"%s\"", str)));
-
-		if (oid == InvalidOid)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("illegal oid: \"%s\"", str)));
-	}
-	else
-	{
-		/*
-		 * There is no Oid passed, so create a new one
-		 */
-		oid = DatumGetObjectId(DirectFunctionCall1(lo_creat,
-								   Int32GetDatum(INV_READ | INV_WRITE)));
-		if (oid == InvalidOid)
-			/* internal error */
-			elog(ERROR, "InvalidOid returned from lo_creat");
-	}
-
-	result = (Blob *) palloc(sizeof(Blob));
-
-	*result = oid;
-
-	return (result);
-}
-
-/*
- * This simply outputs the Oid of the Blob as a string.
- */
-char *
-lo_out(Blob * addr)
-{
-	char	   *result;
-
-	if (addr == NULL)
-		return (NULL);
-
-	result = (char *) palloc(32);
-	snprintf(result, 32, "%u", *addr);
-	return (result);
-}
-
-/*
- * This function converts Blob to oid.
- *
- * eg: select lo_export(raster::oid,'/path/file') from table;
- *
- */
-Oid
-lo_oid(Blob * addr)
-{
-	if (addr == NULL)
-		return InvalidOid;
-	return (Oid) (*addr);
-}
-
-/*
- * This function is used so we can convert oid's to lo's
- *
- * ie:	insert into table values(lo_import('/path/file')::lo);
- *
- */
-Blob *
-lo(Oid oid)
-{
-	Blob	   *result = (Blob *) palloc(sizeof(Blob));
+/* forward declarations */
+Datum		lo_manage(PG_FUNCTION_ARGS);
 
-	*result = oid;
-	return (result);
-}
 
 /*
- * This handles the trigger that protects us from orphaned large objects
+ * This is the trigger that protects us from orphaned large objects
  */
 PG_FUNCTION_INFO_V1(lo_manage);
 
@@ -144,11 +39,10 @@ lo_manage(PG_FUNCTION_ARGS)
 	TupleDesc	tupdesc;		/* Tuple Descriptor				*/
 	HeapTuple	rettuple;		/* Tuple to be returned			*/
 	bool		isdelete;		/* are we deleting?				*/
-	HeapTuple	newtuple = NULL;	/* The new value for tuple		*/
+	HeapTuple	newtuple;		/* The new value for tuple		*/
 	HeapTuple	trigtuple;		/* The original value of tuple	*/
 
-	if (!CALLED_AS_TRIGGER(fcinfo))
-		/* internal error */
+	if (!CALLED_AS_TRIGGER(fcinfo))		/* internal error */
 		elog(ERROR, "not fired by trigger manager");
 
 	/*
@@ -168,9 +62,12 @@ lo_manage(PG_FUNCTION_ARGS)
 	/* Are we deleting the row? */
 	isdelete = TRIGGER_FIRED_BY_DELETE(trigdata->tg_event);
 
-	/* Get the column were interested in */
+	/* Get the column we're interested in */
 	attnum = SPI_fnumber(tupdesc, args[0]);
 
+	if (attnum <= 0)
+		elog(ERROR, "column \"%s\" does not exist", args[0]);
+
 	/*
 	 * Handle updates
 	 *
@@ -182,7 +79,7 @@ lo_manage(PG_FUNCTION_ARGS)
 		char	   *orig = SPI_getvalue(trigtuple, tupdesc, attnum);
 		char	   *newv = SPI_getvalue(newtuple, tupdesc, attnum);
 
-		if (orig != NULL && (newv == NULL || strcmp(orig, newv)))
+		if (orig != NULL && (newv == NULL || strcmp(orig, newv) != 0))
 			DirectFunctionCall1(lo_unlink,
 								ObjectIdGetDatum(atooid(orig)));
 
@@ -196,7 +93,6 @@ lo_manage(PG_FUNCTION_ARGS)
 	 * Handle deleting of rows
 	 *
 	 * Here, we unlink the large object associated with the managed attribute
-	 *
 	 */
 	if (isdelete)
 	{

contrib/lo/lo.sql.in

@@ -1,62 +1,29 @@
 --
---	PostgreSQL code for LargeObjects
+--	PostgreSQL code for managed Large Objects
 --
---	$PostgreSQL: pgsql/contrib/lo/lo.sql.in,v 1.12 2005/01/29 22:35:02 tgl Exp $
---
---
---	Create the data type
+--	$PostgreSQL: pgsql/contrib/lo/lo.sql.in,v 1.13 2005/06/23 00:06:37 tgl Exp $
 --
 
--- used by the lo type, it takes an oid and returns an lo object
-
 -- Adjust this setting to control where the objects get created.
 SET search_path = public;
 
-CREATE FUNCTION lo_in(cstring)
-RETURNS lo
-AS 'MODULE_PATHNAME'
-LANGUAGE C IMMUTABLE STRICT;
-
--- used by the lo type, it returns the oid of the object
-CREATE FUNCTION lo_out(lo)
-RETURNS cstring
-AS 'MODULE_PATHNAME'
-LANGUAGE C IMMUTABLE STRICT;
-
--- finally the type itself
-CREATE TYPE lo (
-	INTERNALLENGTH = 4,
-	EXTERNALLENGTH = variable,
-	INPUT = lo_in,
-	OUTPUT = lo_out
-);
-
--- this returns the oid associated with a lo object
-CREATE FUNCTION lo_oid(lo)
-RETURNS oid
-AS 'MODULE_PATHNAME'
-LANGUAGE C IMMUTABLE STRICT;
+--
+--	Create the data type ... now just a domain over OID
+--
 
--- same function, named to allow it to be used as a type coercion, eg:
---    CREATE TABLE a (image lo);
---    SELECT image::oid FROM a;
---
-CREATE FUNCTION oid(lo)
-RETURNS oid
-AS 'MODULE_PATHNAME', 'lo_oid'
-LANGUAGE C IMMUTABLE STRICT;
-CREATE CAST (lo as oid) WITH FUNCTION oid(lo) AS IMPLICIT;
+CREATE DOMAIN lo AS pg_catalog.oid;
 
--- this allows us to convert an oid to a managed lo object
--- ie: insert into test values (lo_import('/fullpath/file')::lo);
-CREATE FUNCTION lo(oid)
-RETURNS lo
-AS 'MODULE_PATHNAME'
-LANGUAGE C IMMUTABLE STRICT;
-CREATE CAST (oid as lo) WITH FUNCTION lo(oid) AS IMPLICIT;
+--
+-- For backwards compatibility, define a function named lo_oid.
+--
+-- The other functions that formerly existed are not needed because
+-- the implicit casts between a domain and its underlying type handle them.
+--
+CREATE FUNCTION lo_oid(lo) RETURNS pg_catalog.oid AS
+'SELECT $1::pg_catalog.oid' LANGUAGE SQL STRICT IMMUTABLE;
 
 -- This is used in triggers
 CREATE FUNCTION lo_manage()
-RETURNS trigger
+RETURNS pg_catalog.trigger
 AS 'MODULE_PATHNAME'
 LANGUAGE C;

contrib/lo/lo_drop.sql

@@ -1,15 +1,12 @@
 --
--- This removes the type (and a test table)
+-- This removes the LO type
 -- It's used just for development
 --
 
 -- Adjust this setting to control where the objects get created.
 SET search_path = public;
 
--- remove our test table
-DROP TABLE a;
-
--- now drop the type and associated C functions
+-- drop the type and associated functions
 DROP TYPE lo CASCADE;
 
 -- the trigger function has no dependency on the type, so drop separately