[IQUG] [iqug] 16.0 index rebuilds

Louie, David David.Louie at blackrock.com
Mon Oct 7 07:09:03 MST 2019

All we did we FP and tested with this.

Can we flip the bits back if we do run into load issues?

Thanks Mark.


From: Mark Mumy <markdmumy at gmail.com>
Sent: Monday, October 7, 2019 9:57 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

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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.


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On Oct 7, 2019, at 08:51, Louie, David <David.Louie at blackrock.com<mailto: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?)


From: Mark Mumy <markdmumy at gmail.com<mailto:markdmumy at gmail.com>>
Sent: Monday, October 7, 2019 9:37 AM
To: Louie, David <David.Louie at blackrock.com<mailto:David.Louie at blackrock.com>>
Cc: iqug at dssolutions.com<mailto:iqug at dssolutions.com>; Venuturapalli, Sharan <sharan.venuturapalli at blackrock.com<mailto: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.


Sent from my mobile device

On Oct 7, 2019, at 08:09, Louie, David <David.Louie at blackrock.com<mailto: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?


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