Re: Cannot change archive_command with a reload

On 2/2/14, 9:51 AM, Raghavendra wrote:
>
> On Sun, Feb 2, 2014 at 9:56 PM, CS DBA <cs_dba(at)consistentstate(dot)com
> <mailto:cs_dba(at)consistentstate(dot)com>> wrote:
>
> On 2/2/14, 9:19 AM, Raghavendra wrote:
>>
>>
>> On Sun, Feb 2, 2014 at 9:22 PM, CS DBA
>> <cs_dba(at)consistentstate(dot)com <mailto:cs_dba(at)consistentstate(dot)com>>
>> wrote:
>>
>> Hi all;
>>
>> we have a cluster running with an archive command that is
>> failing.
>> I tried a reload and the value does not change
>>
>>
>> Reload with new value won't work until you fix the failing
>> archive_command.
>>
>> Eg:-
>>
>> ps -ef | grep arch
>> postgres 29743 29736 0 Jan30 ? 00:00:00 postgres:
>> archiver process failed on 00000001000000010000003D
>>
>> and it might cause same error you are experiencing as
>>
>> postgres=# select set_config('archive_command','cp %p
>> /opt/PostgreSQL/9.3/a93/%f',false);
>> ERROR: parameter "archive_command" cannot be changed now
>>
>> So, fix the archive_command first and then give new changes.
>>
>> Tried a set_config and I get this error:
>>
>> select set_config ('archive_command', 'cp %p /data/wal_tmp/%f
>> && mv /data/wal_tmp/%f /data/wal/&f', 'false');
>> ERROR: parameter "archive_command" cannot be changed now
>>
>>
>> If your archive_command pointing to "/data/wal_tmp" then please
>> ensure that directory exists there. If that directory not present
>> then archive process fail to copy the transaction logs. When
>> archiver process in failed state you cannot apply any new changes
>> to the archive_command it will fail.
>>
>> Also, am surprised to see "mv" command, basically the
>> archive_command meant to have a copies of pg_xlogs but not any OS
>> related directory movements.
>
> we want to copy the file to /data/wal_tmp, then do a mv to
> /data/wal so our process that ships a copy to the standby servers
> never see's a partial file (since it watches /data/wal)
>
>
> 'cp %p /data/wal_tmp/%f && mv /data/wal_tmp/%f /data/wal/&f',
>
> Seems you are missing something here, you have two action commands in
> your archive_command. One is copy "cp" and another is "mv" move. Once
> you are copying file to the directory you are moving that entire
> directory and not keeping the place available for archiver process to
> copy next file in that location on its next arrival.
>
> Because, every transaction logs first go to archive directory as you
> mentioned "cp %p /data/wal_tmp/%f". Next it will execute the other
> command too since its one command string, i.e, move "mv
> /data/wal_tmp/%f /data/wal&f".
>
> Hence, you need to have unique place for archives and it should not be
> disturbed in any case. If you want to ship a copy to standby server
> then have another directory with same set of copies at OS level.
>
> --Raghav
>
My issue is the &f instead of %f at the end. However here's the intent:

if the first command is true (cp %p /data/wal_tmp/%f) then I want the
second command to execute (mv /data/wal_tmp/%f /data/wal/%f)

since both directories are in the same file system the mv is immediate
so any process watching for files to show up in /data/wal will never see
a partial file