Re: MD5 sums of large objects

On Sun, Apr 08, 2007 at 07:03:17PM +0200, Dirk Jagdmann wrote:
> I have a database containing lots of large objects. Now I'd like to
> compare large objects in my database and I thought of having a
> function which creates a hashsum (MD5, SHA-1 or whatever) of my large
> object, so I can use that in queries:
> 
> create function lo_md5(id oid) returns text...

Something like this might work:

create function lo_md5(id oid) returns text as $$
declare fd        integer; size      integer; hashval   text; INV_READ  constant integer := 262144; SEEK_SET  constant
integer:= 0; SEEK_END  constant integer := 2;
 
begin fd := lo_open(id, INV_READ); size := lo_lseek(0, 0, SEEK_END); perform lo_lseek(0, 0, SEEK_SET); hashval:=
md5(loread(fd,size)); perform lo_close(fd); return hashval;
 
end;
$$ language plpgsql stable strict;

For hash functions other than MD5 see contrib/pgcrypto.

-- 
Michael Fuhr