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't create 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, "Error message: %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);
}