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-- ==============================================================
-- GNUmed database schema change script
--
-- License: GPL v2 or later
-- Author: karsten.hilbert@gmx.net
--
-- ==============================================================
\set ON_ERROR_STOP 1
--set default_transaction_read_only to off;
-- --------------------------------------------------------------
create or replace function gm.lo_chunked_md5(oid, int)
returns text
language 'plpgsql'
stable strict
as '
DECLARE
lo_id alias for $1;
chunk_size alias for $2;
_lo_fd integer;
_lo_size integer;
_chunk_count integer;
_remainder integer;
_md5_concat text;
INV_READ constant integer := x''40000''::integer;
SEEK_SET constant integer := 0;
SEEK_END constant integer := 2;
BEGIN
-- check for existence of lo_id ?
_lo_fd := lo_open(lo_id, INV_READ);
-- get size
_lo_size := lo_lseek(_lo_fd, 0, SEEK_END);
PERFORM lo_close(_lo_fd); -- move further down if loread() proves faster
-- calculate chunks and remainder
_chunk_count := _lo_size / chunk_size;
_remainder := _lo_size % chunk_size;
-- loop over chunks
_md5_concat := '''';
FOR _chunk_id in 1.._chunk_count LOOP
_md5_concat := _md5_concat || md5(lo_get(lo_id, (_chunk_id - 1) * chunk_size, chunk_size));
-- using loread() may be faster (as it directly accesses the
-- existing lo_fd and thusly does not need to re-open the LO
-- each round)
END LOOP;
-- add remainder
_md5_concat := _md5_concat || md5(lo_get(lo_id, _chunk_count * chunk_size, _remainder));
return md5(_md5_concat);
END;';
comment on function gm.lo_chunked_md5(oid, int) is 'Function to create a chunked md5 sum on arbitrarily large LARGE OBJECTs.';
-- --------------------------------------------------------------
select gm.log_script_insertion('v21-gm-md5.sql', '21.0');
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