Ok, attached is the lo type, which goes some way with Large Object

Orphaning that occurs with JDBC & ODBC.

Contents:

contrib/lo/Makefile contrib/lo/README contrib/lo/lo.c contrib/lo/lo.sql.in

These are just test stuff - not essential

contrib/lo/test.sql contrib/lo/drop.sql

Peter Mount

contrib/lo/Makefile

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+#
+#	PostgreSQL lo type
+#
+#	Makefile pinched from the ip-mac contrib package
+#
+#	$Id: Makefile,v 1.1 1998/06/16 07:07:11 momjian Exp $
+
+SRCDIR= ../../src
+
+include $(SRCDIR)/Makefile.global
+
+CONTRIBDIR=$(LIBDIR)/modules
+
+CFLAGS+= $(CFLAGS_SL) -I$(SRCDIR)/include
+
+ifdef REFINT_VERBOSE
+CFLAGS+= -DREFINT_VERBOSE
+endif
+
+TARGETS= lo$(DLSUFFIX) lo.sql
+
+CLEANFILES+= $(TARGETS)
+
+all:: $(TARGETS)
+
+install:: all $(CONTRIBDIR)
+	for f in *$(DLSUFFIX); do $(INSTALL) -c $$f $(CONTRIBDIR)/$$f; done
+
+$(CONTRIBDIR):
+	mkdir -p $(CONTRIBDIR)
+
+%.sql: %.sql.in
+	rm -f $@; \
+	C=`pwd`; \
+	sed -e "s:_OBJWD_:$(CONTRIBDIR):g" \
+	    -e "s:_DLSUFFIX_:$(DLSUFFIX):g" < $< > $@
+
+clean: 
+	rm -f $(TARGETS) *.o

contrib/lo/README

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+PostgreSQL type extension for managing Large Objects
+----------------------------------------------------
+
+$Id: README,v 1.1 1998/06/16 07:07:11 momjian Exp $
+
+Overview
+
+One of the problems with the JDBC driver (and this affects the ODBC driver
+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
+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.
+
+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.
+
+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);
+
+Here, a trigger is created for each column that contains a lo type.
+
+Issues
+
+* dropping a table will still orphan any objects it contains, as the trigger
+  is not actioned.
+
+  For now, precede the 'drop table' with 'delete from {table}'. However, this
+  could be fixed by having 'drop table' perform an additional
+
+      'select lo_unlink({colname}::oid) from {tablename}'
+
+  for each column, before actually dropping the table.
+
+* 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/drop.sql

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+--
+-- This removes the type (and a test table)
+-- It's used just for development
+--
+
+-- remove our test table
+drop table a;
+
+-- now drop any sql based functions associated with the lo type
+drop function oid(lo);
+
+-- now drop the type
+drop type lo;
+
+-- as the type is gone, remove the C based functions
+drop function lo_in(opaque);
+drop function lo_out(opaque);
+drop function lo(oid);
+drop function lo_manage();
+
+-- the lo stuff is now removed from the system

contrib/lo/lo.c

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+/*
+ *	PostgreSQL type definitions for managed LargeObjects.
+ *
+ *	$Id: lo.c,v 1.1 1998/06/16 07:07:11 momjian Exp $
+ *
+ */
+
+#include <stdio.h>
+
+#include <postgres.h>
+#include <utils/palloc.h>
+
+/* Required for largeobjects */
+#include <libpq/libpq-fs.h>
+#include <libpq/be-fsstubs.h>
+
+/* Required for SPI */
+#include <executor/spi.h>
+
+/* Required for triggers */
+#include <commands/trigger.h>
+
+/* required for tolower() */
+
+/*
+ *	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	*/
+HeapTuple	lo_manage(void);		/* Trigger handler			*/
+
+/*
+ * This creates a large object, and set's 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, "%d", &oid);
+	  
+	  if (count < 1)
+		{
+		  elog(ERROR, "lo_in: error in parsing \"%s\"", str);
+		  return (NULL);
+		}
+	  
+	  if(oid < 0)
+		{
+		  elog(ERROR, "lo_in: illegal oid \"%s\"", str);
+		  return (NULL);
+		}
+	}
+  else
+	{
+	  /*
+	   * There is no Oid passed, so create a new one
+	   */
+	  oid = lo_creat(INV_READ|INV_WRITE);
+	  if(oid == InvalidOid)
+		{
+		  elog(ERROR,"lo_in: InvalidOid returned from lo_creat");
+		  return (NULL);
+		}
+	}
+  
+  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);
+  sprintf(result,"%d",*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));
+  *result = oid;
+  return (result);
+}
+
+/*
+ * This handles the trigger that protects us from orphaned large objects
+ */
+HeapTuple
+lo_manage(void)
+{
+  int attnum;					/* attribute number to monitor	*/
+  char **args;					/* Args containing attr name	*/
+  TupleDesc	tupdesc;			/* Tuple Descriptor				*/
+  HeapTuple	rettuple;			/* Tuple to be returned			*/
+  bool		isdelete;			/* are we deleting?				*/
+  HeapTuple newtuple=NULL;		/* The new value for tuple		*/
+  HeapTuple trigtuple;			/* The original value of tuple	*/
+  
+  if (!CurrentTriggerData)
+	elog(ERROR, "lo: triggers are not initialized");
+  
+  /*
+   * Fetch some values from CurrentTriggerData
+   */
+  newtuple	= CurrentTriggerData->tg_newtuple;
+  trigtuple	= CurrentTriggerData->tg_trigtuple;
+  tupdesc	= CurrentTriggerData->tg_relation->rd_att;
+  args		= CurrentTriggerData->tg_trigger->tgargs;
+  
+  /* tuple to return to Executor */
+  if (TRIGGER_FIRED_BY_UPDATE(CurrentTriggerData->tg_event))
+	rettuple = newtuple;
+  else
+	rettuple = trigtuple;
+  
+  /* Are we deleting the row? */
+  isdelete = TRIGGER_FIRED_BY_DELETE(CurrentTriggerData->tg_event);
+  
+  /* Were done with it */
+  CurrentTriggerData = NULL;
+  
+  /* Get the column were interested in */
+  attnum = SPI_fnumber(tupdesc,args[0]);
+  
+  /*
+   * Handle updates
+   *
+   * Here, if the value of the monitored attribute changes, then the
+   * large object associated with the original value is unlinked.
+   */
+  if(newtuple!=NULL) {
+	char *orig = SPI_getvalue(trigtuple,tupdesc,attnum);
+	char *newv = SPI_getvalue(newtuple,tupdesc,attnum);
+	
+	if((orig != newv && (orig==NULL || newv==NULL)) || (orig!=NULL && newv!=NULL && strcmp(orig,newv)))
+	  lo_unlink(atoi(orig));
+	
+	if(newv)
+	  pfree(newv);
+	if(orig)
+	  pfree(orig);
+  }
+  
+  /*
+   * Handle deleting of rows
+   *
+   * Here, we unlink the large object associated with the managed attribute
+   *
+   */
+  if(isdelete) {
+	char *orig = SPI_getvalue(trigtuple,tupdesc,attnum);
+	
+	if(orig != NULL) {
+	  lo_unlink(atoi(orig));
+	  
+	  pfree(orig);
+	}
+  }
+  
+  return (rettuple);
+}

contrib/lo/lo.sql.in

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+--
+--	PostgreSQL code for LargeObjects
+--
+--	$Id: lo.sql.in,v 1.1 1998/06/16 07:07:11 momjian Exp $
+--
+
+load '_OBJWD_/lo_DLSUFFIX_';
+
+--
+--	Create the data type
+--
+
+-- used by the lo type, it takes an oid and returns an lo object
+create function lo_in(opaque)
+	returns opaque
+	as '_OBJWD_/lo_DLSUFFIX_'
+	language 'c';
+
+-- used by the lo type, it returns the oid of the object
+create function lo_out(opaque)
+	returns opaque
+	as '_OBJWD_/lo_DLSUFFIX_'
+	language 'c';
+
+-- 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 '_OBJWD_/lo_DLSUFFIX_'
+	language 'c';
+
+-- 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 '_OBJWD_/lo_DLSUFFIX_'
+	language 'c';
+
+-- This is used in triggers
+create function lo_manage()
+	returns opaque
+	as '_OBJWD_/lo_DLSUFFIX_'
+	language 'c';
+
+-- This allows us to map lo to oid
+--
+-- eg:
+--    create table a (image lo);
+--    select image::oid from a;
+--
+create function oid(lo) returns oid as 'select lo_oid($1)' language 'sql';
+

contrib/lo/test.sql

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+--
+-- This runs some common tests against the type
+--
+-- It's used just for development
+--
+
+-- ignore any errors here - simply drop the table if it already exists
+drop table a;
+
+-- create the test table
+create table a (fname name,image lo);
+
+-- insert a null object
+insert into a values ('null');
+
+-- insert an empty large object
+insert into a values ('empty','');
+
+-- insert a large object based on a file
+insert into a values ('/etc/group',lo_import('/etc/group')::lo);
+
+-- now select the table
+select * from a;
+
+-- this select also returns an oid based on the lo column
+select *,image::oid from a;
+
+-- now test the trigger
+create trigger t_a before update or delete on a for each row execute procedure lo_manage(image);
+
+-- insert
+insert into a values ('aa','');
+select * from a where fname like 'aa%';
+
+-- update
+update a set image=lo_import('/etc/group')::lo where fname='aa';
+select * from a where fname like 'aa%';
+
+-- update the 'empty' row which should be null
+update a set image=lo_import('/etc/hosts')::lo where fname='empty';
+select * from a where fname like 'empty%';
+update a set image=null where fname='empty';
+select * from a where fname like 'empty%';
+
+-- delete the entry
+delete from a where fname='aa';
+select * from a where fname like 'aa%';
+
+-- This deletes the table contents. Note, if you comment this out, and
+-- expect the drop table to remove the objects, think again. The trigger
+-- doesn't get thrown by drop table.
+delete from a;
+
+-- finally drop the table
+drop table a;
+
+-- end of tests