I have written a number of functions in C that return BYTEA type. I have
compiled and run on both Windows and Linux, 32-bit and 64-bit, PostgreSQL
versions 9.3 and 9.4.
My functions return BYTEA data to the caller. The problem is that memory usage
grows until there is no memory left on the host, at which point an error is
returned. If I drop the connection (e.g. by quitting from pqsql), the memory is
returned.
I wrote the following minimal function to test palloc() and BYTEA return
behaviour, and found that this minimal program also exhibits the unbounded
memory growth problem.
C source code:
PG_FUNCTION_INFO_V1(test_palloc);
Datum test_palloc()
{
bytea *test_ret;
int test_len = 1024;
test_ret = (bytea *)palloc(test_len + VARHDRSZ);
SET_VARSIZE(test_ret, test_len + VARHDRSZ);
PG_RETURN_BYTEA_P(test_ret);
}
Function definition:
CREATE OR REPLACE FUNCTION test_palloc() RETURNS BYTEA
AS E'<path to shared library>', test_palloc' LANGUAGE C IMMUTABLE STRICT;
psql commands to reproduce the problem:
\o out.txt
SELECT ids.*, test_palloc() FROM GENERATE_SERIES(1, 1000000) ids;
At the completion of the above command, host memory will have been consumed but
not released back to the system. After quitting psql (\q), memory is released.
Is this expected behaviour or a bug? Am I doing something wrong? How can I
return a BYTEA type from a C library function without having to drop the
connection in order to recover the allocated memory that is returned to the
caller?
Regards,
John
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