Re: log file sync waits / slow response time at log switches

You can also try to set log_archive_dest_3='service=STDBY_DG LGWR
SYNC=parallel AFFIRM OPTIONAL REOPEN=30' and create standby logfiles on the
standby side. That should make LGWR write to the standby side simultaneously
to the primary side.
Or if you don't want that maybe use the ARCH process instead of the LGWR?

Finn



On 2/14/08, Mayen.Shah@xxxxxxxxxx <Mayen.Shah@xxxxxxxxxx> wrote:
>
>
> Gerald,
>
> log switch will not complete until active (current) log is archived to all
> destinations (optional and mandatory). If your remote archiving is slow, it
> will slowdown log switch and database at primary site may appear hung.
>
> you may use following parameter to achieve what you want.
>
> _LOG_ARCHIVE_CALLOUT='LOCAL_FIRST=TRUE'
>
> Please refer to metalink notes 3227858.8 and 403979.1
>
> HTH
>
> Mayen Shah
>
>
>
>
>
>
>
> *"Gerald Cunningham" <gcunningham@xxxxxxxxxxxxxxxxxxxxxxxx>*
> Sent by: oracle-l-bounce@xxxxxxxxxxxxx
>
> Feb 14 2008 02:21 PM   Please respond to
> gcunningham@xxxxxxxxxxxxxxxxxxxxxxxx
>
>    To
> oracle-l@xxxxxxxxxxxxx  cc
>   Subject
> log file sync waits / slow response time at log switches
>
>
>
> Hi all,
>
> My 10046 tracing is showing a lot of "log file sync" waits. Also, users
> log files (processes are doing DML) are showing
> spikes in response time that match the times of the log switches.
>
> This is a physical Data Guard implementation with 1 primary / 1 standby.
> Oracle 9.2.0.8 64-bit on Solaris.
>
> From the alert log, it appears that Oracle is waiting until the redo
> information has been written to the standby site
> before it switches the primary's redo logs.
>
> log_archive_dest_3 was set to mandatory, so I tried setting it to optional
> (see line "c" below). This didn't appear to
> have any effect. Here is an excerpt of my primary alert log:
>
> ===
> (a) Thu Feb 14 17:39:23 2008
>    LGWR: Completed archiving  log 2 thread 1 sequence 155723
>    Creating archive destination LOG_ARCHIVE_DEST_3: 'STDBY_DG'
>    LNS0 started with pid=249, OS id=9556
> (b) Thu Feb 14 17:39:32 2008
>    LGWR: Beginning to archive log 3 thread 1 sequence 155724
>    Thread 1 advanced to log sequence 155274
>      Current log# 3 seq# 155724 mem# 0:
> /dbdata_11/oradata/prod/redo03_1.log
>      Current log# 3 seq# 155724 mem# 1:
> /dbdata_12/oradata/prod/redo03_2.log
>    Thu Feb 14 17:39:32 2008
>    ARC1: Evaluating archive   log 2 thread 1 sequence 155723
>    ARC1: Archive destination LOG_ARCHIVE_DEST_3: Previously completed
>    ARC1: Beginning to archive log 2 thread 1 sequence 155723
>    Creating archive destination LOG_ARCHIVE_DEST_2:
> '/dbdata_15/oradata/prod/ARCHIVE/arch_1_155723.arc'
>    Creating archive destination LOG_ARCHIVE_DEST_1:
> '/dbdata_10/oradata/prod/ARCHIVE/arch_1_155723.arc'
>    Thu Feb 14 17:39:45 2008
>    ARC1: Completed archiving  log 2 thread 1 sequence 155723
>    Thu Feb 14 17:41:45 2008
> (c) ALTER SYSTEM SET log_archive_dest_3='service=STDBY_DG LGWR ASYNC=20480
> AFFIRM OPTIONAL REOPEN=30' SCOPE=MEMORY;
> (d) Thu Feb 14 17:43:17 2008
>    LGWR: Completed archiving  log 3 thread 1 sequence 155724
>    Creating archive destination LOG_ARCHIVE_DEST_3: 'STDBY_DG'
>    LNS0 started with pid=221, OS id=12045
> (e) Thu Feb 14 17:43:35 2008
>    LGWR: Beginning to archive log 1 thread 1 sequence 155725
>    Thread 1 advanced to log sequence 155275
>      Current log# 1 seq# 155725 mem# 0:
> /dbdata_16/oradata/prod/redo01_1.log
>      Current log# 1 seq# 155725 mem# 1:
> /dbdata_17/oradata/prod/redo01_2.log
> ===
> Questions:
>
> - I believe the time from a-to-b and d-to-e is where my users are waiting,
> because Oracle hasn't switched the redo log
> yet. Is this true? These 2 waits are 9 seconds and 18 seconds! Sometimes
> they are longer, or shorter, but this is typical.
>
> - I thought when I changed dest_3 to optional, Oracle would switch the
> local/primary first, then do the "standby stuff".
> Why isn't it?
>
> - Is the time from a-to-b and c-to-d for creating the new LNS0 process? If
> so, is there any way to have a persistent LNS0 process?
>
> - Is there any way to force the local/primary redo to switch *before*
> doing any standby work?
>
>
> Thanks very much for any help!
>
> Jerry
>

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