Re: array_agg(DISTINCT) caused a segmentation fault

On Mon, 13 Feb 2023 at 18:29, Fujii Masao <masao.fujii@oss.nttdata.com> wrote:

=# SELECT array_agg(distinct val) FROM (SELECT NULL AS val FROM generate_series(1, 2)) hoge;
LOG:  server process (PID 76507) was terminated by signal 11: Segmentation fault: 11
DETAIL:  Failed process was running: SELECT array_agg(distinct val) FROM (SELECT NULL AS val FROM generate_series(1, 2)) hoge;

I've now pushed a fix for it and included your test.  To get it to
crash it needed to be a byref aggregate without a strict transition
function.  There are not too many of those, which is probably why
nobody noticed this before.

I've encountered an issue that could have the same title but it still reproduced after the fix.
The following query:
SELECT array_agg(DISTINCT a ORDER BY a DESC)
          FROM (VALUES (1),(1.0),(NULL)) v(a);

Invokes valgrind-detected error:
==00:00:00:03.708 2686358== Invalid read of size 4
==00:00:00:03.708 2686358==    at 0x76C4AE: GetMemoryChunkMethodID (mcxt.c:195)
==00:00:00:03.708 2686358==    by 0x76C4AE: pfree (mcxt.c:1439)
==00:00:00:03.708 2686358==    by 0x3FD547: ExecEvalPreOrderedDistinctSingle (execExprInterp.c:4258)
==00:00:00:03.708 2686358==    by 0x3FF203: ExecInterpExpr (execExprInterp.c:1772)
==00:00:00:03.708 2686358==    by 0x418792: ExecEvalExprSwitchContext (executor.h:344)
==00:00:00:03.708 2686358==    by 0x418792: advance_aggregates (nodeAgg.c:823)
==00:00:00:03.708 2686358==    by 0x41A12A: agg_retrieve_direct (nodeAgg.c:2446)
==00:00:00:03.708 2686358==    by 0x41A294: ExecAgg (nodeAgg.c:2171)
==00:00:00:03.708 2686358==    by 0x40AD3F: ExecProcNodeFirst (execProcnode.c:464)
==00:00:00:03.708 2686358==    by 0x40337F: ExecProcNode (executor.h:262)
==00:00:00:03.708 2686358==    by 0x40337F: ExecutePlan (execMain.c:1633)
==00:00:00:03.708 2686358==    by 0x403542: standard_ExecutorRun (execMain.c:364)
==00:00:00:03.708 2686358==    by 0x40360E: ExecutorRun (execMain.c:308)
==00:00:00:03.708 2686358==    by 0x5EB971: PortalRunSelect (pquery.c:924)
==00:00:00:03.708 2686358==    by 0x5ED31B: PortalRun (pquery.c:768)
==00:00:00:03.708 2686358==  Address 0xfffffffffffffff8 is not stack'd, malloc'd or (recently) free'd
==00:00:00:03.708 2686358==
...
==00:00:00:03.708 2686358==
==00:00:00:03.708 2686358== Exit program on first error (--exit-on-first-error=yes)
2023-02-13 10:26:39.276 MSK [2686332] LOG:  server process (PID 2686358) exited with exit code 1
2023-02-13 10:26:39.276 MSK [2686332] DETAIL:  Failed process was running: SELECT array_agg(DISTINCT a ORDER BY a DESC)
              FROM (VALUES (1),(1.0),(NULL)) v(a);

(Without valgrind I get SIGSEGV here.)
The first bad commit is 1349d2790 again (but before 80ef92675 an assertion failure can be seen).

Best regards,
Alexander