Problem with lo_export() and lo_import() from remote machine.

Post by Purusothaman A
Hi all,
I have problem while using "lo_export()" and "lo_import()" from remote
system.
****
select lo_export(img_file, 'E:\\temp\\1001.jpg') from master where emp_id =
'1001';
insert into master(img_file) values(lo_import('E:\\temp\\1001.jpg')) where
emp_id = '1001';
Here column "img_file" is OID data type.
The above query works, if I enter from PostgreSQL server machine.
But the same query fails, if I enter from any other client machine in my
LAN.
All other queries work well from remote machine, which do not deal OID data
type column.
any suggestions would be appreciated.

Please, RTFM - http://www.postgresql.org/docs/current/static/lo-funcs.html

Quote:

"The server-side lo_import and lo_export functions behave considerably
differently from their client-side analogs. These two functions read and
write files in the server's file system, using the permissions of the
database's owning user. Therefore, their use is restricted to
superusers. In contrast, the client-side import and export functions
read and write files in the client's file system, using the permissions
of the client program. The client-side functions can be used by any
PostgreSQL user."

--
Milen A. Radev

---------------------------(end of broadcast)---------------------------
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Purusothaman A

2006-09-09 11:49:26 UTC

Hi Milen A. Radev,

Thank you for your response.

I have read this in PostgreSQL documentation.

I usually log in to postgresql server with admin username.

But whatever its, according to documentation, if client machine's user has
write access
permission, this query should successfully be executed.

Both PostgreSQL server/client are Windows XP machines.

Any suggestion???

:)
Purusothaman A

Post by Purusothaman A
Hi all,
I have problem while using "lo_export()" and "lo_import()" from remote
system.
****
select lo_export(img_file, 'E:\\temp\\1001.jpg') from master where

emp_id =

Post by Purusothaman A
'1001';
insert into master(img_file) values(lo_import('E:\\temp\\1001.jpg'))

where

Post by Purusothaman A
emp_id = '1001';
Here column "img_file" is OID data type.
The above query works, if I enter from PostgreSQL server machine.
But the same query fails, if I enter from any other client machine in my
LAN.
All other queries work well from remote machine, which do not deal OID

data

Post by Purusothaman A
type column.
any suggestions would be appreciated.

Please, RTFM - http://www.postgresql.org/docs/current/static/lo-funcs.html
"The server-side lo_import and lo_export functions behave considerably
differently from their client-side analogs. These two functions read and
write files in the server's file system, using the permissions of the
database's owning user. Therefore, their use is restricted to
superusers. In contrast, the client-side import and export functions
read and write files in the client's file system, using the permissions
of the client program. The client-side functions can be used by any
PostgreSQL user."
--
Milen A. Radev
---------------------------(end of broadcast)---------------------------
TIP 5: don't forget to increase your free space map settings

Martijn van Oosterhout

2006-09-09 12:06:13 UTC

Post by Purusothaman A
I usually log in to postgresql server with admin username.
But whatever its, according to documentation, if client machine's user has
write access
permission, this query should successfully be executed.

Read carefully, you are using the server-side functions, therefore:

"These two functions read and write files in the server's file system,
using the permissions of the database's owning user."

What your client user is is irrelevent. Perhaps you actually want to
use the client-side functions?

Have a nice day,

Post by Purusothaman A
From each according to his ability. To each according to his ability to litigate.

Purusothaman A

2006-09-11 09:15:10 UTC

Hi Martijn van Oosterhout,

Thanks for your valuable reply.

Yes I misunderstood the documentation.

Then, I searched PostgreSQL documentation for equivalent client-side
functions.
But I found only C programming APIs instead of SQL functions.

I want functions which is usable in SQL statements.

Can you give example or equivalent client side function syntax?

Thanks in advance.

:)
Purusothaman A

Post by Purusothaman A
I usually log in to postgresql server with admin username.
But whatever its, according to documentation, if client machine's user

has

Post by Purusothaman A
write access
permission, this query should successfully be executed.

"These two functions read and write files in the server's file system,
using the permissions of the database's owning user."
What your client user is is irrelevent. Perhaps you actually want to
use the client-side functions?
Have a nice day,
--

Post by Purusothaman A
From each according to his ability. To each according to his ability to

litigate.
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Martijn van Oosterhout

2006-09-11 09:38:19 UTC

Short answer, you can't. The database server can obviously only access
things on the database server. Since SQL is also executed on the
server, no SQL statements can access stuff on the client computer.

If you want to load a file on the client side to the server, you need
to open the file and copy it over using the lo_ functions. There no way
(IIRC) to access the contents of large objects from just SQL.

Hope this helps,

Post by Purusothaman A
Hi Martijn van Oosterhout,
Thanks for your valuable reply.
Yes I misunderstood the documentation.
Then, I searched PostgreSQL documentation for equivalent client-side
functions.
But I found only C programming APIs instead of SQL functions.
I want functions which is usable in SQL statements.
Can you give example or equivalent client side function syntax?
Thanks in advance.
:)
Purusothaman A

Post by Purusothaman A
I usually log in to postgresql server with admin username.
But whatever its, according to documentation, if client machine's user

has

Post by Purusothaman A
write access
permission, this query should successfully be executed.

Post by Purusothaman A
From each according to his ability. To each according to his ability to

litigate.
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Post by Purusothaman A
From each according to his ability. To each according to his ability to litigate.

Purusothaman A

2006-09-11 09:57:09 UTC

Thanks Martijn van Oosterhout,

So, I have to write my own wrapper function upon the functions below.
1. Oid lo_import(PGconn *conn, const char *filename);
2. int lo_export(PGconn *conn, Oid lobjId, const char *filename);

Am I right?

:)
Purusothaman A

Post by Martijn van Oosterhout
Short answer, you can't. The database server can obviously only access
things on the database server. Since SQL is also executed on the
server, no SQL statements can access stuff on the client computer.
If you want to load a file on the client side to the server, you need
to open the file and copy it over using the lo_ functions. There no way
(IIRC) to access the contents of large objects from just SQL.
Hope this helps,

Post by Purusothaman A
I usually log in to postgresql server with admin username.
But whatever its, according to documentation, if client machine's

user

Post by Martijn van Oosterhout
has

Post by Purusothaman A
write access
permission, this query should successfully be executed.

http://svana.org/kleptog/

Post by Purusothaman A
From each according to his ability. To each according to his ability

Post by Martijn van Oosterhout
litigate.
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Post by Purusothaman A
From each according to his ability. To each according to his ability to

litigate.
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Martijn van Oosterhout

2006-09-11 10:03:36 UTC

Not sure why you need a wrapper (you didn't say which language you were
using) but those functions work exactly like the version you put in the
SQL statements, except the filenames are for the client computer with
client permissions.

Hope this helps,

Post by Purusothaman A
From each according to his ability. To each according to his ability to litigate.

Purusothaman A

2006-09-11 10:15:26 UTC

Thanks Martijn van Oosterhout and Marco Bizzarri.

But, according to syntax of client side lo_import and lo_export, we should
have 2 variable PGconn (for esatablished connection) and lobjld (imported
file ID in PostgreSQL).

I don't know how to do this in SQL statements.

pls give me sample client side sql statements.

:)
Purusothaman A

Post by Purusothaman A
From each according to his ability. To each according to his ability to

litigate.
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Marco Bizzarri

2006-09-11 10:56:11 UTC

I will try to explain it with a sample session: this is for creating
and writing a blob.

From the psql prompt (> are the commands, the other are the results).
begin ;

BEGIN;

SELECT lo_creat(131072) ;

lo_creat
----------
198705
(1 row)
(this is the OID number of the newly created large object).

select lo_open(198705, 131072) ;

lo_open
---------
0
(1 row)

(this is the file handler which you will use in the operations).

SELECT lowrite(0, 'aaaa');

lowrite
---------
4
(1 row)

(you wrote 4 character in a large object)

select lo_close(0);

lo_close
----------
0
(1 row)

(you closed the file).

commit ;

COMMIT

In this way, you created a new large object, and stored a string of 4
bytes inside of it.

Regards
Marco

Thanks Martijn van Oosterhout and Marco Bizzarri.
But, according to syntax of client side lo_import and lo_export, we should
have 2 variable PGconn (for esatablished connection) and lobjld (imported
file ID in PostgreSQL).
I don't know how to do this in SQL statements.
pls give me sample client side sql statements.
:)
Purusothaman A

Post by Purusothaman A
From each according to his ability. To each according to his ability to

litigate.
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-----END PGP SIGNATURE-----

--
Marco Bizzarri
http://notenotturne.blogspot.com/

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Martijn van Oosterhout

2006-09-11 11:02:10 UTC

Post by Marco Bizzarri
I will try to explain it with a sample session: this is for creating
and writing a blob.

Oh, I was looking for lo_read/lo_write, which don't exist. It's
loread/lowrite. Inconsonistant naming is irritating.

It doesn't help the OPs problem with lo_import/lo_export though.

Have a nice day,

Post by Marco Bizzarri
From each according to his ability. To each according to his ability to litigate.

Purusothaman A

2006-09-11 13:30:00 UTC

Hi Marco Bizzarri and Martijn van Oosterhout,

Thanks for your valuable reply.

I am trying to execute all query from VC++ through
CDatabase::ExecuteSQL(sQueryString) function call.

ie, via programming, not by manual entering query statements.
so, in my situation I can construct a string and pass on to this function to
execute the query string.

Whatever the string I pass to ExecuteSQL() function, gets executed and I
cannot get any result retured from the passed query string [like OID -
198705, from lo_create()].

Now, can you suggest me how to achieve it?

And one more clarification, what is the value 131072? How can I get this
vlaue?

According to PostgreSQL documentation, they gave C Syntax as client side
function.

Should I use those C API calls?

:)
Purusothaman A

Post by Marco Bizzarri
I will try to explain it with a sample session: this is for creating
and writing a blob.
From the psql prompt (> are the commands, the other are the results).

begin ;

BEGIN;

SELECT lo_creat(131072) ;

lo_creat
----------
198705
(1 row)
(this is the OID number of the newly created large object).

select lo_open(198705, 131072) ;

lo_open
---------
0
(1 row)
(this is the file handler which you will use in the operations).

SELECT lowrite(0, 'aaaa');

lowrite
---------
4
(1 row)
(you wrote 4 character in a large object)

select lo_close(0);

lo_close
----------
0
(1 row)
(you closed the file).

commit ;

COMMIT
In this way, you created a new large object, and stored a string of 4
bytes inside of it.
Regards
Marco

Thanks Martijn van Oosterhout and Marco Bizzarri.
But, according to syntax of client side lo_import and lo_export, we

should

have 2 variable PGconn (for esatablished connection) and lobjld

(imported

file ID in PostgreSQL).
I don't know how to do this in SQL statements.
pls give me sample client side sql statements.
:)
Purusothaman A

Post by Purusothaman A
From each according to his ability. To each according to his ability

litigate.
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--
Marco Bizzarri
http://notenotturne.blogspot.com/

Marco Bizzarri

2006-09-11 14:49:37 UTC

Post by Purusothaman A
Hi Marco Bizzarri and Martijn van Oosterhout,
Thanks for your valuable reply.
I am trying to execute all query from VC++ through
CDatabase::ExecuteSQL(sQueryString) function call.
ie, via programming, not by manual entering query statements.
so, in my situation I can construct a string and pass on to this function to
execute the query string.
Whatever the string I pass to ExecuteSQL() function, gets executed and I
cannot get any result retured from the passed query string [like OID -
198705, from lo_create()].

I'm not an expert in VC++. I think you should obtain some sort of
ResultSet object. You could then check that.

Post by Purusothaman A
Now, can you suggest me how to achieve it?
And one more clarification, what is the value 131072? How can I get this
vlaue?

This is actually 0x20000 value in decimal. Check large object
interface in postgresql documentation (C API).

Post by Purusothaman A
According to PostgreSQL documentation, they gave C Syntax as client side
function.
Should I use those C API calls?

If you're working from inside C, you can check:

http://www.postgresql.org/docs/8.1/static/lo-interfaces.html

Regards
Marco

Post by Purusothaman A
:)
Purusothaman A

Post by Marco Bizzarri
I will try to explain it with a sample session: this is for creating
and writing a blob.
From the psql prompt (> are the commands, the other are the results).

begin ;

BEGIN;

SELECT lo_creat(131072) ;

lo_creat
----------
198705
(1 row)
(this is the OID number of the newly created large object).

select lo_open(198705, 131072) ;

lo_open
---------
0
(1 row)
(this is the file handler which you will use in the operations).

SELECT lowrite(0, 'aaaa');

lowrite
---------
4
(1 row)
(you wrote 4 character in a large object)

select lo_close(0);

lo_close
----------
0
(1 row)
(you closed the file).

commit ;

COMMIT
In this way, you created a new large object, and stored a string of 4
bytes inside of it.
Regards
Marco

Thanks Martijn van Oosterhout and Marco Bizzarri.
But, according to syntax of client side lo_import and lo_export, we

should

have 2 variable PGconn (for esatablished connection) and lobjld

(imported

file ID in PostgreSQL).
I don't know how to do this in SQL statements.
pls give me sample client side sql statements.
:)
Purusothaman A

Post by Purusothaman A
From each according to his ability. To each according to his ability

litigate.
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iD8DBQFFBTR4IB7bNG8LQkwRAvhPAJ9KHp9DO1EjPqbkGwBdaSaKx5J90wCfQtZ8

ijq1n/SgAlwIiEgDI6zfICg=
=Xk7N
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--
Marco Bizzarri
http://notenotturne.blogspot.com/

--
Marco Bizzarri
http://notenotturne.blogspot.com/

---------------------------(end of broadcast)---------------------------
TIP 6: explain analyze is your friend

Purusothaman A

2006-09-12 10:34:07 UTC

Thank you Marco Bizzarri.

My solution would be C API.

Thanks for you prompt response.

:)
Purusothaman A

function to

Post by Purusothaman A
execute the query string.
Whatever the string I pass to ExecuteSQL() function, gets executed and I
cannot get any result retured from the passed query string [like OID -
198705, from lo_create()].

I'm not an expert in VC++. I think you should obtain some sort of
ResultSet object. You could then check that.

Post by Purusothaman A
Now, can you suggest me how to achieve it?
And one more clarification, what is the value 131072? How can I get this
vlaue?

This is actually 0x20000 value in decimal. Check large object
interface in postgresql documentation (C API).

Post by Purusothaman A
According to PostgreSQL documentation, they gave C Syntax as client side
function.
Should I use those C API calls?

http://www.postgresql.org/docs/8.1/staticI /lo-interfaces.html
Regards
Marco

Post by Purusothaman A
:)
Purusothaman A

Post by Marco Bizzarri
I will try to explain it with a sample session: this is for creating
and writing a blob.
From the psql prompt (> are the commands, the other are the results).

begin ;

BEGIN;

SELECT lo_creat(131072) ;

lo_creat
----------
198705
(1 row)
(this is the OID number of the newly created large object).

select lo_open(198705, 131072) ;

lo_open
---------
0
(1 row)
(this is the file handler which you will use in the operations).

SELECT lowrite(0, 'aaaa');

lowrite
---------
4
(1 row)
(you wrote 4 character in a large object)

select lo_close(0);

lo_close
----------
0
(1 row)
(you closed the file).

commit ;

COMMIT
In this way, you created a new large object, and stored a string of 4
bytes inside of it.
Regards
Marco

Thanks Martijn van Oosterhout and Marco Bizzarri.
But, according to syntax of client side lo_import and lo_export, we

should

have 2 variable PGconn (for esatablished connection) and lobjld

(imported

file ID in PostgreSQL).
I don't know how to do this in SQL statements.
pls give me sample client side sql statements.
:)
Purusothaman A

Post by Purusothaman A
Thanks Martijn van Oosterhout,
So, I have to write my own wrapper function upon the functions

below.

Post by Purusothaman A
1. Oid lo_import(PGconn *conn, const char *filename);
2. int lo_export(PGconn *conn, Oid lobjId, const char

*filename);

Not sure why you need a wrapper (you didn't say which language you

were

using) but those functions work exactly like the version you put in

the

SQL statements, except the filenames are for the client computer

with

client permissions.
Hope this helps,
--

http://svana.org/kleptog/

Post by Purusothaman A
From each according to his ability. To each according to his

ability

Post by Purusothaman A
to

litigate.
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=Xk7N
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--
Marco Bizzarri
http://notenotturne.blogspot.com/

Marco Bizzarri

2006-09-11 10:07:06 UTC

Actually, you can use direclty the lo_create, lo_open, lo_read and
lo_write directly into your SQL code, instead of having to write a
wrapper function. It is not simple, but it can be done.

I don't have a general example: we have done this in a couple of our
projects, one being public availabe (www.paflow.it): look in the
Documents.py source, and look for the lo_xxx queries.

This is indipendent from the fact that client and server are running
on the same server.

Regards
Marco

Post by Purusothaman A
Thanks Martijn van Oosterhout,
So, I have to write my own wrapper function upon the functions below.
1. Oid lo_import(PGconn *conn, const char *filename);
2. int lo_export(PGconn *conn, Oid lobjId, const char *filename);
Am I right?
:)
Purusothaman A
Short answer, you can't. The database server can obviously only access
things on the database server. Since SQL is also executed on the
server, no SQL statements can access stuff on the client computer.
If you want to load a file on the client side to the server, you need
to open the file and copy it over using the lo_ functions. There no way
(IIRC) to access the contents of large objects from just SQL.
Hope this helps,