[IQUG] [iqug] 16.0 index rebuilds

Mark Mumy markdmumy at gmail.com
Mon Oct 7 06:56:49 MST 2019


Tiered HGs don’t help with compression.  They only affect load performance in some situations.   It’s not a guarantee and I’ve seen it add more load and overhead.  Like anything it must be tested to make sure that it gives you a gain and doesn’t hurt performance.  

All a retier does is flip a few bits on the HG structure to tell it to use the tiered structure the next time a load happens.  The base HG stays the same which is why it runs quickly.  

If you haven’t tested this yet, I would not do this.  It really does require testing on your part to make sure you don’t see a degradation.  It has happened so I am always cautious with this.  

Mark
 
========================

Sent from my mobile device

> On Oct 7, 2019, at 08:51, Louie, David <David.Louie at blackrock.com> wrote:
> 
> 
> Hi Mark,
>  
> We tested on 16.0 and it’s late in the game to target 16.1 as it’s an unknown to us unfortunately.
>  
> SAP support says we need to change all HG indices to tiered to take advantage of the efficiencies in 16.0 which include better load efficiencies and compression.
>  
> This certainly is contrary to the approach we talked about last year which was to just rebuild all FPs.
>  
> Why does the retier only take seconds and if it does only take seconds why not do them ( what’s a miss on this?)
>  
> Thanks
> David
>  
>  
> From: Mark Mumy <markdmumy at gmail.com> 
> Sent: Monday, October 7, 2019 9:37 AM
> To: Louie, David <David.Louie at blackrock.com>
> Cc: iqug at dssolutions.com; Venuturapalli, Sharan <sharan.venuturapalli at blackrock.com>
> Subject: Re: [IQUG] [iqug] 16.0 index rebuilds
>  
> External Email: Use caution with links and attachments
> 
> Just to plant the seed....    if you don’t go to 16.1 sp03 or later you will need to do another rebuild then too.  
>  
> Why are you going to tiered HG?   First, that operation takes seconds.   More importantly are you sure that you need them?  I know that the benefit is hit or miss.  I’ve not seen much help with them but some have.  
>  
> Other than that, the process looks fine.  
> 
> Mark
>  
> ========================
>  
> Sent from my mobile device
> 
> 
> On Oct 7, 2019, at 08:09, Louie, David <David.Louie at blackrock.com> wrote:
> 
> 
> Hello All,
>  
> Another 16.0 migration set of questions.  
>  
> Our 15.4 db is 50+ TB and contains a large 30 TB table.  We know we need to rebuild FP indices post upgrade and then rebuild HG as tiered,  (sp_iqrebuildindex(<table>, HG, retier).   We know we will need to do a phased approach as it is impossible to do this much work over 1 weekend.
>  
> Weekend 1   upgrade in place to 16.0,  rebuild all critical tables FP indices
> Weekend 2   rebuild all large tables FP indices  (30TB table included)   Not all of the FP indices on the 30 TB table will be done and will need to be phased
> Weekend 3  and beyond   continue to rebuild the 30 TB FP indices and misc HG indices as tiered.
>  
> First is the approach correct and is what most shops are doing?
>  
> Second would there be a performance hit as we cannot get all HG indices Tiered and partial FP rebuilds on various table ( like the 30 TB table)
>  
> We have a problem creating HG indices on the 30 TB table. ( dropping LF indices to make them HG).  Ran out of temp space and our server stack traced and needed to be rebooted.  
>  
> Is there a way to determine how much temp space is required to recreate an HG index on a table?
>  
> Are LF indices completely deprecated in 16.0 and will we need to recreate them as HG’s day 1?
>  
> Thanks
> David
>  
>  
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