PostgreSQL 10: Segmentation fault when using GROUPING SETS with allunsortable columns - Mailing list pgsql-hackers

Hi,

I have found a case which could get segmentation fault when using GROUPING SETS.
It occurs when columns in GROUPING SETS are all unsortable but hashable.

Attached grouping_sets_segv.zip include module to reproduce this problem.

I think it made from below change.

https://www.postgresql.org/docs/current/static/release-10.html#id-1.11.6.8.5.3.6
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Allow hashed aggregation to be used with grouping sets (Andrew Gierth)
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https://github.com/postgres/postgres/commit/b5635948ab165b6070e7d05d111f966e07570d81


bt from attached grouping_sets_segv.zip is like below.
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Program terminated with signal 11, Segmentation fault.
#0  0x0000000000797855 in consider_groupingsets_paths (root=0x11fe078, grouped_rel=0x120cfc0, path=0x11ff488,
is_sorted=0'\000',  
    can_hash=1 '\001', target=0x11ffb20, gd=0x11fedb8, agg_costs=0x7fffed813850, dNumGroups=400) at planner.c:4205
4205                            unhashed_rollup = lfirst(l_start);
Missing separate debuginfos, use: debuginfo-install glibc-2.17-196.el7.x86_64 keyutils-libs-1.5.8-3.el7.x86_64
krb5-libs-1.15.1-8.el7.x86_64libcom_err-1.42.9-7.el7.x86_64 libselinux-2.2.2-6.el7.x86_64
libxml2-2.9.1-6.el7_2.3.x86_64openssl-libs-1.0.1e-42.el7.x86_64 pcre-8.32-14.el7.x86_64 tde_for_pg10-1.2.0-0.el7.x86_64
xz-libs-5.1.2-9alpha.el7.x86_64zlib-1.2.7-17.el7.x86_64 
(gdb) bt
#0  0x0000000000797855 in consider_groupingsets_paths (root=0x11fe078, grouped_rel=0x120cfc0, path=0x11ff488,
is_sorted=0'\000',  
    can_hash=1 '\001', target=0x11ffb20, gd=0x11fedb8, agg_costs=0x7fffed813850, dNumGroups=400) at planner.c:4205
#1  0x0000000000797404 in create_grouping_paths (root=0x11fe078, input_rel=0x11fe290, target=0x11ffb20,
agg_costs=0x7fffed813850, 
    gd=0x11fedb8) at planner.c:4045
#2  0x0000000000793a06 in grouping_planner (root=0x11fe078, inheritance_update=0 '\000', tuple_fraction=0) at
planner.c:1895
#3  0x0000000000791ed8 in subquery_planner (glob=0x11b2a50, parse=0x11b2448, parent_root=0x0, hasRecursion=0 '\000',
tuple_fraction=0)
    at planner.c:862
#4  0x0000000000790d9e in standard_planner (parse=0x11b2448, cursorOptions=256, boundParams=0x0) at planner.c:334
#5  0x0000000000790b30 in planner (parse=0x11b2448, cursorOptions=256, boundParams=0x0) at planner.c:210
#6  0x00000000008756a1 in pg_plan_query (querytree=0x11b2448, cursorOptions=256, boundParams=0x0) at postgres.c:796
#7  0x00000000008757ce in pg_plan_queries (querytrees=0x11febc8, cursorOptions=256, boundParams=0x0) at postgres.c:862
#8  0x0000000000875a92 in exec_simple_query (
    query_string=0x11b1060 "select c1,c2 from testtbl_gouping_sets group by grouping sets(c1,c2);") at postgres.c:1027
#9  0x0000000000879dc2 in PostgresMain (argc=1, argv=0x115d570, dbname=0x115d3d8 "si2", username=0x112dfc0 "postgres")
    at postgres.c:4088
#10 0x00000000007dddb7 in BackendRun (port=0x1155fc0) at postmaster.c:4405
#11 0x00000000007dd53f in BackendStartup (port=0x1155fc0) at postmaster.c:4077
#12 0x00000000007d9a47 in ServerLoop () at postmaster.c:1755
#13 0x00000000007d9086 in PostmasterMain (argc=1, argv=0x112be90) at postmaster.c:1363
#14 0x00000000007184a2 in main (argc=1, argv=0x112be90) at main.c:228
(gdb) p l_start
$1 = (ListCell *) 0x0
(gdb) p gd->rollups
$2 = (List *) 0x0
(gdb)
---------------

Look at related source I found that,
In planner.c:preprocess_grouping_sets, we do not update gd->rollups if all of columns in
GROUPING SETS are unsortable but hashable.

After that in planner.c:consider_groupingsets_paths we used gd->rollups and made the SEGV above.

Not yet fully understand the related commit, but I think it is fine to put
ERRCODE_FEATURE_NOT_SUPPORTED error from preprocess_grouping_sets when all columns in
GROUPING SETS are unsortable. Is that right?

I have tried to write a patch (attached).
Could anyone confirm for me?


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Thanks and best regards,
Dang Minh Huong
NEC Solution Innovators, Ltd.
http://www.nec-solutioninnovators.co.jp/en/