RE: Poor man's standby monitoring
- From: Yong Huang <yong321@xxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Thu, 23 Dec 2010 10:22:57 -0800 (PST)
On a database we use ARCH to ship redo, a query on v$managed_standby
can't detect the gap at all:
SQL> select process, status, client_process, thread#, sequence# from
v$managed_standby;
PROCESS STATUS CLIENT_P THREAD# SEQUENCE#
--------- ------------ -------- ---------- ----------
ARCH CLOSING ARCH 1 34409
ARCH CLOSING ARCH 1 34410
RFS IDLE UNKNOWN 0 0
RFS IDLE UNKNOWN 0 0
RFS IDLE UNKNOWN 0 0
RFS IDLE UNKNOWN 0 0
RFS IDLE UNKNOWN 0 0
RFS IDLE UNKNOWN 0 0
RFS IDLE UNKNOWN 0 0
MRP0 WAIT_FOR_LOG N/A 2 28378
RFS IDLE UNKNOWN 0 0
because it doesn't tell us which sequence for thread 2 has arrived. A
query of v$archied_log (as Don hinted earlier) works:
SQL> select x.thread#, x.cur_log, y.apl_log, x.cur_log - y.apl_log gap
2 from (select thread#, max(sequence#) cur_log from v$log group by thread#)
x,
3 (select thread#, max(sequence#) apl_log from v$archived_log where
applied = 'YES' group by thread#) y
4 where x.thread# = y.thread#
5 order by 1;
THREAD# CUR_LOG APL_LOG GAP
---------- ---------- ---------- ----------
1 34411 34372 39
2 28418 28377 41
...
We have 1 day's delay of redo apply so the gaps are expected.
Yong Huang
--- On Thu, 12/23/10, Yong Huang <yong321@xxxxxxxxx> wrote:
> > This works for an exclusive primary, but doesn't quite work for
> > a RAC primary (since there are multiple redo threads):
> > ...
>
> The SQL below works for RAC when LGWR is shipping redo:
>
> SQL> select x.sequence# - y.sequence# gap
> 2 from (select thread#, sequence# from
> v$managed_standby where process = 'MRP0') x,
> 3 (select thread#,
> sequence# from v$managed_standby where process = 'RFS' and
> client_process = 'LGWR') y
> 4 where x.thread# = y.thread#;
>
> GAP
> ----------
> 0
>
> It queries the view twice. There may be a way to query it
> only once.
>
> Yong Huang
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