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Tombart
Asked: 2021-09-07 13:29:58 +0800 CST

如何调试 PostgreSQL 分段错误？

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我有一个不断崩溃的 PostgreSQL 13 实例：

LOG:  server process (PID 10722) was terminated by signal 11: Segmentation fault
DETAIL:  Failed process was running: COMMIT
LOG:  terminating any other active server processes
WARNING:  terminating connection because of crash of another server process
DETAIL:  The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.

我已更新/etc/postgresql/13/main/pg_ctl.conf以包含核心转储

pg_ctl_options = '--core-files'

并重新启动postgresql服务。现在它似乎允许核心转储：

$ for f in `pgrep postgres`; do cat /proc/$f/limits | grep core; done
Max core file size        unlimited            unlimited            bytes

gdb回溯给出以下输出

$ gdb /usr/lib/postgresql/13/bin/postgres 13/main/core.postgres.12264

Program terminated with signal SIGSEGV, Segmentation fault.
#0  slot_deform_heap_tuple (natts=5, offp=0x557cc2e60720, tuple=<optimized out>, slot=0x557cc2e606d8) at ./build/../src/backend/executor/execTuples.c:930
930     ./build/../src/backend/executor/execTuples.c: No such file or directory.
(gdb) bt
#0  slot_deform_heap_tuple (natts=5, offp=0x557cc2e60720, tuple=<optimized out>, slot=0x557cc2e606d8) at ./build/../src/backend/executor/execTuples.c:930
#1  tts_buffer_heap_getsomeattrs (slot=0x557cc2e606d8, natts=5) at ./build/../src/backend/executor/execTuples.c:695
#2  0x0000557cc1d3998c in slot_getsomeattrs_int (slot=slot@entry=0x557cc2e606d8, attnum=5) at ./build/../src/backend/executor/execTuples.c:1912
#3  0x0000557cc1d28fba in slot_getsomeattrs (attnum=<optimized out>, slot=0x557cc2e606d8) at ./build/../src/include/executor/tuptable.h:344
#4  ExecInterpExpr (state=0x557cc2e620a8, econtext=0x557cc2ea1768, isnull=<optimized out>) at ./build/../src/backend/executor/execExprInterp.c:482
#5  0x0000557cc1d5548d in ExecEvalExprSwitchContext (isNull=0x7ffdd2599507, econtext=0x557cc2ea1768, state=0x557cc2e620a8) at ./build/../src/include/executor/executor.h:322
#6  ExecQual (econtext=0x557cc2ea1768, state=0x557cc2e620a8) at ./build/../src/include/executor/executor.h:391
#7  MJFillInner (node=0x557cc2ea1558) at ./build/../src/backend/executor/nodeMergejoin.c:494
#8  0x0000557cc1d55ce8 in ExecMergeJoin (pstate=0x557cc2ea1558) at ./build/../src/backend/executor/nodeMergejoin.c:1353
#9  0x0000557cc1d2cc83 in ExecProcNode (node=0x557cc2ea1558) at ./build/../src/include/executor/executor.h:248
#10 ExecutePlan (execute_once=<optimized out>, dest=0x557cc2e1a630, direction=<optimized out>, numberTuples=0, sendTuples=<optimized out>, operation=CMD_SELECT, use_parallel_mode=<optimized out>, planstate=0x557cc2ea1558, 
    estate=0x557cc2ea12f8) at ./build/../src/backend/executor/execMain.c:1632
#11 standard_ExecutorRun (queryDesc=0x557cc2e1a5a0, direction=<optimized out>, count=0, execute_once=<optimized out>) at ./build/../src/backend/executor/execMain.c:350
#12 0x00007f0ec05ae09d in pgss_ExecutorRun (queryDesc=0x557cc2e1a5a0, direction=ForwardScanDirection, count=0, execute_once=<optimized out>) at ./build/../contrib/pg_stat_statements/pg_stat_statements.c:1045
#13 0x0000557cc1cdbcd4 in PersistHoldablePortal (portal=portal@entry=0x557cc2d44b78) at ./build/../src/backend/commands/portalcmds.c:407
#14 0x0000557cc1ff95f9 in HoldPortal (portal=portal@entry=0x557cc2d44b78) at ./build/../src/backend/utils/mmgr/portalmem.c:642
#15 0x0000557cc1ff9e7d in PreCommit_Portals (isPrepare=isPrepare@entry=false) at ./build/../src/backend/utils/mmgr/portalmem.c:738
#16 0x0000557cc1c001c4 in CommitTransaction () at ./build/../src/backend/access/transam/xact.c:2087
#17 0x0000557cc1c015d5 in CommitTransactionCommand () at ./build/../src/backend/access/transam/xact.c:3085
#18 0x0000557cc1ea211d in finish_xact_command () at ./build/../src/backend/tcop/postgres.c:2662
#19 0x0000557cc1ea4703 in exec_simple_query (query_string=0x557cc2c9cd28 "COMMIT") at ./build/../src/backend/tcop/postgres.c:1264
#20 0x0000557cc1ea6143 in PostgresMain (argc=<optimized out>, argv=argv@entry=0x557cc2cf6c68, dbname=<optimized out>, username=<optimized out>) at ./build/../src/backend/tcop/postgres.c:4339
#21 0x0000557cc1e25bcd in BackendRun (port=0x557cc2ce94d0, port=0x557cc2ce94d0) at ./build/../src/backend/postmaster/postmaster.c:4526
#22 BackendStartup (port=0x557cc2ce94d0) at ./build/../src/backend/postmaster/postmaster.c:4210
#23 ServerLoop () at ./build/../src/backend/postmaster/postmaster.c:1739
#24 0x0000557cc1e26b41 in PostmasterMain (argc=5, argv=<optimized out>) at ./build/../src/backend/postmaster/postmaster.c:1412
#25 0x0000557cc1b70f4f in main (argc=5, argv=0x557cc2c96c30) at ./build/../src/backend/main/main.c:210

添加log_statement = 'all'到/etc/postgresql/13/main/postgresql.conf并没有真正的帮助，因为postmaster会立即终止所有进程并且查询不会写入日志。

这是strace运行后的输出COMMIT

[pid 20006] pwrite64(29, "COMMIT", 6, 15936) = 6
[pid 20006] pwrite64(29, "\0", 1, 15942) = 1
[pid 20006] close(29)                   = 0
[pid 20006] --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0x10} ---
[pid 20006] +++ killed by SIGSEGV (core dumped) +++
<... select resumed> )                  = ? ERESTARTNOHAND (To be restarted if no handler)
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_DUMPED, si_pid=20006, si_uid=108, si_status=SIGSEGV, si_utime=0, si_stime=0} ---
wait4(-1, [{WIFSIGNALED(s) && WTERMSIG(s) == SIGSEGV && WCOREDUMP(s)}], WNOHANG, NULL) = 20006
write(2, "2021-09-08 13:38:51.853 UTC [299"..., 198) = 198
write(2, "2021-09-08 13:38:51.853 UTC [299"..., 88) = 88
kill(19324, SIGQUIT)                    = 0
kill(-19324, SIGQUIT)                   = 0
kill(19331, SIGQUIT)                    = 0
kill(-19331, SIGQUIT)                   = 0
kill(19320, SIGQUIT)                    = 0
kill(-19320, SIGQUIT)                   = 0
kill(19319, SIGQUIT)                    = 0
kill(-19319, SIGQUIT)                   = 0
kill(19321, SIGQUIT)                    = 0
kill(-19321, SIGQUIT)                   = 0
kill(19322, SIGQUIT)                    = 0
kill(-19322, SIGQUIT)                   = 0
kill(19323, SIGQUIT)                    = 0
kill(-19323, SIGQUIT)                   = 0
wait4(-1, 0x7ffe90814374, WNOHANG, NULL) = 0
rt_sigreturn({mask=[]})                 = -1 EINTR (Interrupted system call)
rt_sigprocmask(SIG_SETMASK, ~[ILL TRAP ABRT BUS FPE SEGV CONT SYS RTMIN RT_1], NULL, 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
select(7, [5 6], NULL, NULL, {tv_sec=5, tv_usec=0}) = ? ERESTARTNOHAND (To be restarted if no handler)
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=19320, si_uid=108, si_status=2, si_utime=14, si_stime=3} ---

有没有办法追溯执行的确切 SQL 查询？

debian postgresql segmentation-fault

1 个回答

  1. Best Answer

    首先为您的发行版安装调试符号，对于 Debian 发行版：

    apt install gdb postgresql-13-dbgsym

    跳转到包含一些queryDesc变量的帧，例如12：

    (gdb) frame 12
#12 0x00007f0ec05ae09d in pgss_ExecutorRun (queryDesc=0x557cc302b7d0, direction=ForwardScanDirection, count=0, execute_once=<optimized out>) at ./build/../contrib/pg_stat_statements/pg_stat_statements.c:1045
1045    in ./build/../contrib/pg_stat_statements/pg_stat_statements.c

    打印该变量：

    (gdb) p queryDesc
$1 = (QueryDesc *) 0x557cc302b7d0

    现在在等号之后复制上面的行并使用取消引用它*

    (gdb) p *(QueryDesc *) 0x557cc302b7d0
$6 = {operation = CMD_SELECT, plannedstmt = 0x557cc300e218, 
  sourceText = 0x557cc302b370 "\n", ' ' <repeats 12 times>, "DECLARE \"categoryPagePhotoUrl_image_urls\" CURSOR WITH HOLD FOR\n", ' ' <repeats 12 times>, "SELECT di.itemId, image_number, filename FROM (SELECT *\n", ' ' <repeats 12 times>, "FROM downl"..., snapshot = 0x557cc2e9b188, crosscheck_snapshot = 0x0, dest = 0x557cc302b860, params = 0x0, queryEnv = 0x0, instrument_options = 0, tupDesc = 0x557cc2f7bff8, 
  estate = 0x557cc2cf8d08, planstate = 0x557cc2cf8f68, already_executed = true, totaltime = 0x0}

    它不会为您提供整个查询，但至少可以了解执行查询的表。

    根据gdb输出，我设法隔离了正在执行此类查询的客户端。

    我尝试VACUUM FULL在受影响的表上运行，重建表和索引，切换到副本，使用pg_dump. 尽管如此，该问题仍然存在于数据库副本上。

    最后，我设法隔离了一个最小的 SQL 代码来复制问题。

    $ pg_createcluster 13 main
$ createdb testdb
$ psql -d testdb -f postgresql-segfault.sql
CREATE SCHEMA
CREATE TABLE
COPY 1
ALTER TABLE
BEGIN
CREATE TABLE
DECLARE CURSOR
 itemid  
---------
 1190300
(1 row)

psql:postgresql-segfault:34: server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.
psql:postgresql-segfault:34: fatal: connection to server was lost

    使用复制代码就足以向pgsql -bugs邮件列表报告错误（还有一个网络表单）。结果是重新执行计划的错误，该计划已经在 PostgreSQL 13.4、12.8（以及可能的其他版本）中包含的不稳定游标上完成。

    • 2

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