Re: Support for N synchronous standby servers - take 2 - Mailing list pgsql-hackers

On Mon, Apr 11, 2016 at 8:47 PM, Fujii Masao <masao.fujii@gmail.com> wrote:
> On Mon, Apr 11, 2016 at 5:52 PM, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>> On Mon, Apr 11, 2016 at 1:31 PM, Fujii Masao <masao.fujii@gmail.com> wrote:
>>> On Mon, Apr 11, 2016 at 10:58 AM, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>>>> On Sat, Apr 9, 2016 at 12:32 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>>>> Jeff Janes <jeff.janes@gmail.com> writes:
>>>>>> When I compile now without cassert, I get the compiler warning:
>>>>>
>>>>>> syncrep.c: In function 'SyncRepUpdateConfig':
>>>>>> syncrep.c:878:6: warning: variable 'parse_rc' set but not used
>>>>>> [-Wunused-but-set-variable]
>>>>>
>>>>> If there's a good reason for that to be an Assert, I don't see it.
>>>>> There are no callers of SyncRepUpdateConfig that look like they
>>>>> need to, or should expect not to have to, tolerate errors.
>>>>> I think the way to fix this is to turn the Assert into a plain
>>>>> old test-and-ereport-ERROR.
>>>>>
>>>>
>>>> I've changed the draft patch Amit implemented so that it doesn't parse
>>>> twice(check_hook and assign_hook).
>>>> So assertion that was in assign_hook is no longer necessary.
>>>>
>>>> Please find attached.
>>>
>>> Thanks for the patch!
>>>
>>> When I emptied s_s_names, reloaded the configration file, set it to 'standby1'
>>> and reloaded the configuration file again, the master crashed with
>>> the following error.
>>>
>>> *** glibc detected *** postgres: wal sender process postgres [local]
>>> streaming 0/3015F18: munmap_chunk(): invalid pointer:
>>> 0x00000000024d9a40 ***
>>> ======= Backtrace: =========
>>> *** glibc detected *** postgres: wal sender process postgres [local]
>>> streaming 0/3015F18: munmap_chunk(): invalid pointer:
>>> 0x00000000024d9a40 ***
>>> /lib64/libc.so.6[0x3be8e75f4e]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x97dae2]
>>> ======= Backtrace: =========
>>> /lib64/libc.so.6[0x3be8e75f4e]
>>> postgres: wal sender process postgres [local] streaming
>>> 0/3015F18(set_config_option+0x12cb)[0x982242]
>>> postgres: wal sender process postgres [local] streaming
>>> 0/3015F18(SetConfigOption+0x4b)[0x9827ff]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x97dae2]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x988b4e]
>>> postgres: wal sender process postgres [local] streaming
>>> 0/3015F18(set_config_option+0x12cb)[0x982242]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x98af40]
>>> postgres: wal sender process postgres [local] streaming
>>> 0/3015F18(SetConfigOption+0x4b)[0x9827ff]
>>> postgres: wal sender process postgres [local] streaming
>>> 0/3015F18(ProcessConfigFile+0x9f)[0x98a98b]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x988b4e]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x98af40]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x7b50fd]
>>> postgres: wal sender process postgres [local] streaming
>>> 0/3015F18(ProcessConfigFile+0x9f)[0x98a98b]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x7b359c]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x7b50fd]
>>> postgres: wal sender process postgres [local] streaming
>>> 0/3015F18(exec_replication_command+0x1a7)[0x7b47b6]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x7b359c]
>>> postgres: wal sender process postgres [local] streaming
>>> 0/3015F18(PostgresMain+0x772)[0x8141b6]
>>> postgres: wal sender process postgres [local] streaming
>>> 0/3015F18(exec_replication_command+0x1a7)[0x7b47b6]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x7896f7]
>>> postgres: wal sender process postgres [local] streaming
>>> 0/3015F18(PostgresMain+0x772)[0x8141b6]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x788e62]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x7896f7]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x785544]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x788e62]
>>> postgres: wal sender process postgres [local] streaming
>>> 0/3015F18(PostmasterMain+0x1134)[0x784c08]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x785544]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x6ce12e]
>>> /lib64/libc.so.6(__libc_start_main+0xfd)[0x3be8e1ed5d]
>>> postgres: wal sender process postgres [local] streaming
>>> 0/3015F18(PostmasterMain+0x1134)[0x784c08]
>>> postgres: wal sender process postgres [local] streaming 0/3015F18[0x467e99]
>>>
>>
>> Thank you for reviewing.
>>
>> SyncRepUpdateConfig() seems to be no longer necessary.
>
> Really? I was thinking that something like that function needs to
> be called at the beginning of a backend and walsender in
> EXEC_BACKEND case. No?
>

Hmm, in EXEC_BACKEND case, I guess that each child process calls
read_nondefault_variables that parses and validates these
configuration parameters in SubPostmasterMain.
Previous patch didn't apply to HEAD cleanly, attached updated version.

Regards,

--
Masahiko Sawada