So the main thing about goldengate and memory here is that nothing gets written
into a trail file until you type commit. If you have a very large transaction,
you're going to need a lot of memory to retain it in RAM. And Goldengate will
take that RAM - it's very hungry.
Are you running GG on the database server, or on its own server?
I don't know if GG frees-up memory when writing the transaction down for
Bounded Recovery - I'll setup a test case to check that later today - but I
suspect it doesn't as when performing a BR recovery from a failed extract it
loads from the BR files into memory.
Neil Chandler
________________________________
From: oracle-l-bounce@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx> on behalf
of Ls Cheng <exriscer@xxxxxxxxx>
Sent: 14 February 2018 10:42
To: Niall Litchfield
Cc: ORACLE-L
Subject: Re: Golden Gate - cachemgr settings
Hi
I set it to 4G - 8G. The default value is way too much, a few years ago it
caused server swapping and node evictions in one of RAC installations because
huge transactions (50 million rows update transaction) are cached in memory
which is way too much.
Thanks
On Wed, Feb 14, 2018 at 11:20 AM, Niall Litchfield
<niall.litchfield@xxxxxxxxx<mailto:niall.litchfield@xxxxxxxxx>> wrote:
Hi all
We're in the process of implementing Golden Gate. We've observed that by
default on 64bit systems Golden Gate wants 64GB of memory for cache. From
https://docs.oracle.com/goldengate/1212/gg-winux/GWURF/gg_parameters017.htm#GWURF413
" Sets a soft limit for the amount of virtual memory (cache size) that is
available for caching transaction data. On 64-bit systems, the default is 64 GB
"
Reserving 64G of ram for Golden Gate seems an extraordinarily large amount,
especially on a system where multiple GG processes might be running. Similarly
allowing this memory to swap out seems to rather negate the purpose of a cache
:). There's a repeated warning in the docs not to control this without
contacting Oracle Support for guidance. Our engagement with Oracle Support
hasn't exactly been stellar - they're happy to look at individual cases, but
general guidance isn't really in their remit.
So, for folks out there using GG, do you set the CACHESIZE parameter to control
GG memory usage, if so how? Is it really on a case by case basis. If not do you
observe GG really using 64g ram for cache?
--
Niall Litchfield
Oracle DBA
http://www.orawin.info
