Re: RAC install on Linux

From: Neil Chandler <>
Date: Thu, 22 Feb 2018 08:47:09 +0000
Message-ID: <HE1PR1001MB12431CCAAF96247FCE54D03A85CD0_at_HE1PR1001MB1243.EURPRD10.PROD.OUTLOOK.COM>

Transparent Hugepages should be disabled, to prevent the Kernel “helping you out” and causing CPU spikes and unpredictable performance hits.

You should always be using Hugepages.

They give a minor performance improvement and a significant memory saving in terms of the amount of memory needed to handle the pages - less Transaction Lookaside Buffers, which also means less TLB misses (which are expensive).

You are handling the memory chopped up into 2MB pieces instead of 4K. But you also have a single shared memory TLB for Hugepages.

The kernel has less work to do, bookkeeping fewer pointers in the TLB.

You also have contiguous memory allocation and it can’t be swapped.

If you are having problems with Hugepages, you have probably overallocated them (I’ve seen this several times at clients so it’s not uncommon). Hugepages can *only* by used for your SGA’s. All of your SGA’s should fit into the Hugepages and that should generally be no more than about 60% of the total server memory (but there are exceptions), leaving plenty of “normal” memory (small pages) for PGA , O/S and other stuff like monitoring agendas.

As an added bonus, AMM can’t use Hugepages, so your are forced to use ASMM. AMM doesn’t work well and has been kind-of deprecated by oracle anyway - dbca won’t let you setup AMM if the server has more than 4GB of memory.

sent from my phone

On 22 Feb 2018, at 01:50, Cee Pee <<>> wrote:

We turned off hugePages, it gave us trouble in our Oracle/Linux.

On Tue, Feb 20, 2018 at 8:22 PM, Orlando L <<>> wrote:

Thanks Jared. The manual says disable Transparent Huge Pages but use standard HugePages for enhanced performance:

Is that a setting listers use? If so, any warnings or due diligence work? Thanks again.

On Sat, Feb 17, 2018 at 7:59 PM, Jared Still <<>> wrote: Sorry, should have said already disabled on oracle linux, both 6 and 7

sent from my mobile, so expert typos

On Feb 17, 2018 5:10 PM, "Jared Still" <<>> wrote: Re hugepages, only on redhat, already disabled on Linux 7

sent from my mobile, so expert typos

On Feb 12, 2018 8:35 PM, "Orlando L" <<>> wrote: List

We are planning to install Oracle RAC 12.1 on Linux 7.

  1. I am looking for a step by step instruction guide if any one has it. Or point me to a good link. I am more interested in the OS settings, os patches, potential trips, etc,

It should be straight forward till I saw today in the official Grid infrastructure install guide that you should disable Transparent Huge pages in Linux and that it is enabled by default. I started wondering what else I could have missed buried in there.

2) Another thing helpful would be any tool that we could use to simulate the current production load in the new env. I considered RAT, but that is out of qn because of the $


Received on Thu Feb 22 2018 - 09:47:09 CET

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