Re: question on standby (LGWR, ASYNC)
- From: Ankur Shah <desert_moon@xxxxxxxxx>
- To: susanzlam@xxxxxxxxx
- Date: Mon, 20 Sep 2004 12:13:16 -0700
This can be dealt by Implementing SSH port forwarding with 9i Data Guard.
Check out Metalink Doc ID: Note:225633.1 which details about sane and clarifies
the issue....
LGWR ASYNC: ------------ Asynchronously archiving with the LGWR process in
conjunction with SSH port forwarding showed the following characteristics when
compared to the baseline: - Significant reduction in network traffic -
Slight increase in primary database throughput - Minimal increase in cpu usage
When using LGWR to remotely archive in ASYNC mode, the LGWR process does not
wait for each network I/O to complete before proceeding. This behavior is made
possible by the use of an intermediate process, known as a LGWR network server
process (LNS), that performs the actual network I/O and waits for each network
I/O to complete. Each LNS has a user configurable buffer that is used to
accept outbound redo data from the LGWR. This is configured by specifying the
size in 512 byte blocks on the ASYNC attribute in the archivelog destination
parameter. For example ASYNC=2048 indicates a 1Mb buffer. As long as the
LNS process is able to empty this buffer faster than the LGWR can fill it, the
LGWR will never stall. If the LNS cannot keep up, then the buffer will become
full and the LGWR will stall until either sufficient buffer space is freed up
by a successful network transmission or a timeout occurs. Reducing network
traffic in a network with high round trip times (RTT) reduces network server
timeouts due to buffer full conditions, thus reducing the impact to the
primary database throughput. ASYNC can improve the primary database throughput
due to the fact that by compressing the redo traffic, the transfer (in 1 MB
chunks) is quicker and thus the ASYNC buffer doesn't reach full capacity as
often, thereby avoiding the wait that can occur when the buffer is full.
=====================
HTHU
Ankur Shah
Oracle DBA
DHR-GA
Quoting susan lam <susanzlam@xxxxxxxxx>:
> Hi,
> I'm trying to understand the performance impact the
> standby database will have on the primary database
> with Maximum Performance mode (LGWR ASYNC using
> standby redo logs) if the physical standby is not
> able to handle the load generated by the primary db.
> Will there be any?
>
> I read somewhere on metalink that when the LNS detects
> that the async network buffer is full, the primary db
> will halt for a number of seconds before temporary
> switching to ARCH for shipping the logs. Is there a
> best practice as to what I should set the async
> network buffer (ASYNC) to?
>
> I'm using 9204.
>
> TIA.
>
> susan
>
>
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