huge backend processes

maybe i'm doing something wrong here:

CREATE TABLE samples
  (
  mark      abstime,
  subnet    inet,
  bytes_in  float8,
  bytes_out float8
  );
CREATE INDEX samples_mark ON samples (mark);

--- fill it with lots and lots of data

BEGIN WORK;
DECLARE mycurs CURSOR FOR
   SELECT DATE_PART('epoch', mark), subnet, bytes_in, bytes_out
   FROM samples
   WHERE mark >= 'epoch or another date'::abstime;

-- LOOP
FETCH FORWARD 1000 IN mycurs

END WORK;


given the above, actually done using C/libpq, i run my program, which
does a PQclear after each FETCH.

after reading 250000 records, top says:

  PID USERNAME PRI NICE SIZE    RES STATE    TIME   WCPU    CPU COMMAND
13748 postgres105   0 22724K 20588K RUN      3:05 86.14% 86.14% postgres

at some point, it runs out of memory (or something):

     279001 records read (1177 rec/sec)
   testprog: query failed - FETCH FORWARD 1000 IN samples;
   testprog: (7) pqReadData() -- backend closed the channel unexpectedly.
   This probably means the backend terminated abnormally before or while
   processing the request.

i have had this problem with other processes on other tables.

the problem is usually if i am selecting a huge number of records,
and defining some conversion or something in the selected fields.

if i revert my code to (note: less the DATE_PART conversion):

DECLARE mycurs CURSOR FOR
   SELECT mark, subnet, bytes_in, bytes_out
   FROM samples
   WHERE mark >= 'epoch or another date'::abstime;

it works fine.

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[ Jim Mercer    Reptilian Research      jim@reptiles.org   +1 416 410-5633 ]
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