Re: [HACKERS] Backend problem with large objects

On Thu, 4 Feb 1999, Bruce Momjian wrote:

> Applied manually.  The patch did not apply cleanly, and needed a &tuple
> in inv_wrold, not tuple.

In the 4.6.2 release there are no &tuple arguments to inv_wrold around the
patch. Perhaps there is a patch you have applied that I need? Please see
below:

> > > On Tue, 2 Feb 1999, Tatsuo Ishii wrote:
> > > 
> > Ok. I think I have found the source of the problem. Please apply
> > included patches and try again.

Many thanks indeed for this. Unfortunately it doesn't completely work:  it
fixes the problem as reported, but when, instead of writing five
characters, one at a time, I write five at once, the backend dies in
the same place it did before. Here's the C code slightly modified to
reproduce the problem:

#include <stdio.h>
#include "libpq-fe.h"
#include "libpq/libpq-fs.h"

void exec_cmd(PGconn *conn, char *str);

main (int argc, char *argv[])
{  PGconn *conn;  int lobj_fd;  char buf[256];  int ret, i;  Oid lobj_id;
  conn = PQconnectdb("dbname=test");  if (PQstatus(conn) != CONNECTION_OK) {     fprintf(stderr, "Can't connect to
backend.\n");    fprintf(stderr, "ERROR: %s\n", PQerrorMessage(conn));     exit(1);  }  exec_cmd(conn, "BEGIN
TRANSACTION"); PQtrace (conn, stdout);  if ((lobj_id = lo_creat(conn, INV_READ | INV_WRITE)) < 0) {     fprintf(stderr,
"Can'tcreate lobj.\n");     fprintf(stderr, "ERROR: %s\n", PQerrorMessage(conn));     exit(1);  }  if ((lobj_fd =
lo_open(conn,lobj_id, INV_READ | INV_WRITE)) < 0) {     fprintf(stderr, "Can't open lobj.\n");     fprintf(stderr,
"ERROR:%s\n", PQerrorMessage(conn));     exit(1);  }  fprintf(stderr, "lo_open returned fd = %d.\n", lobj_fd);
 
/*  for (i = 0; i < 5; i++) {
*/     if ((ret = lo_write(conn, lobj_fd, "XXXXX", 5)) != 5) {        fprintf(stderr, "Can't write lobj.\n");
fprintf(stderr,"ERROR: %s\n", PQerrorMessage(conn));        exit(1);     }
 
/*  }
*/  if ((ret = lo_lseek(conn, lobj_fd, 1, 0)) != 1) {     fprintf(stderr, "error (%d) lseeking in large object.\n",
ret);    fprintf(stderr, "ERROR: %s\n", PQerrorMessage(conn));     exit(1);  }  if ((ret = lo_write(conn, lobj_fd, "y",
1))!= 1) {     fprintf(stderr, "Can't write lobj.\n");     fprintf(stderr, "ERROR: %s\n", PQerrorMessage(conn));
exit(1); }  if ((ret = lo_lseek(conn, lobj_fd, 3, 0)) != 3) {     fprintf(stderr, "error (%d) lseeking in large
object.\n",ret);     fprintf(stderr, "ERROR: %s\n", PQerrorMessage(conn));     exit(1);  }  if ((ret = lo_write(conn,
lobj_fd,"y", 1)) != 1) {     fprintf(stderr, "Can't write lobj.\n");     fprintf(stderr, "ERROR: %s\n",
PQerrorMessage(conn));    exit(1);  }  ret = lo_close(conn, lobj_fd);  printf("lo_close returned %d.\n", ret);  if
(ret)    fprintf(stderr, "Error message: %s\n", PQerrorMessage(conn));  PQuntrace(conn);  exec_cmd(conn, "END
TRANSACTION"); exit(0);
 
}

void exec_cmd(PGconn *conn, char *str)
{  PGresult *res;
  if ((res = PQexec(conn, str)) == NULL) {     fprintf(stderr, "Error executing %s.\n", str);     fprintf(stderr,
"Errormessage: %s\n", PQerrorMessage(conn));     exit(1);  }  if (PQresultStatus(res) != PGRES_COMMAND_OK) {
fprintf(stderr,"Error executing %s.\n", str);     fprintf(stderr, "Error message: %s\n", PQerrorMessage(conn));
PQclear(res);    exit(1);  }  PQclear(res);
 
}