(gdb) bt
#0  check_string_escape_warning (ychar=92 '\\', yyscanner=0x1a90220) at src/backend/parser/scan.l:1622
#1  0x0000000000ac5982 in core_yylex (yylval_param=0x7ffd7de70830, yylloc_param=0x7ffd7de7082c, yyscanner=0x1a90220) at src/backend/parser/scan.l:746
#2  0x0000000000ac46b1 in base_yylex (lvalp=0x7ffd7de70830, llocp=0x7ffd7de7082c, yyscanner=0x1a90220) at src/backend/parser/parser.c:101
#3  0x0000000000a4f3f9 in base_yyparse (yyscanner=0x1a90220) at src/backend/parser/gram.c:31959
#4  0x0000000000ac460b in raw_parser (str=0x1a8f9f0 "select 'a\\\\bcd' as f1;") at src/backend/parser/parser.c:53
#5  0x0000000000ba6fd9 in pg_parse_query (query_string=0x1a8f9f0 "select 'a\\\\bcd' as f1;") at src/backend/tcop/postgres.c:701
#6  0x0000000000daf4eb in shouldBypassQuery (query_string=0x1a8f9f0 "select 'a\\\\bcd' as f1;") at src/backend/utils/resgroup/resgroup.c:3671
#7  0x0000000000dad3cb in AssignResGroupOnMaster () at src/backend/utils/resgroup/resgroup.c:2597
#8  0x0000000000641b64 in StartTransaction () at src/backend/access/transam/xact.c:2648
#9  0x0000000000642dd5 in StartTransactionCommand () at src/backend/access/transam/xact.c:3659
#10 0x0000000000baa000 in start_xact_command () at src/backend/tcop/postgres.c:2722
#11 0x0000000000ba75c9 in exec_simple_query (query_string=0x1a8f9f0 "select 'a\\\\bcd' as f1;") at src/backend/tcop/postgres.c:1111
#12 0x0000000000bad50c in PostgresMain (argc=1, argv=0x1ae66f0, dbname=0x1ae6568 "postgres", username=0x1ae6548 "yz") at src/backend/tcop/postgres.c:5165
#13 0x0000000000af3b15 in BackendRun (port=0x1ab9b60) at src/backend/postmaster/postmaster.c:5196
#14 0x0000000000af32cb in BackendStartup (port=0x1ab9b60) at src/backend/postmaster/postmaster.c:4887
#15 0x0000000000aeede6 in ServerLoop (receive_encryption_key=false) at src/backend/postmaster/postmaster.c:2060
#16 0x0000000000aee5b6 in PostmasterMain (argc=9, argv=0x1a8a350) at src/backend/postmaster/postmaster.c:1668
#17 0x00000000009238d0 in main (argc=9, argv=0x1a8a350) at src/backend/main/main.c:228