[IQUG] Sybase 16 - FP_NBIT_Autosize_Limit

Rittenhouse, David d.rittenhouse at sap.com
Wed Mar 11 12:46:50 MST 2015


Hi Will,

It appears you are reverse engineering a value based on your desire to use more bits of the n-Bit, and thereby increase your compression ratio.

I am slightly concerned you are increasing the default value by over 30 times.

I don't know what datatypes you are using but I have seen cases where 1m (the default) uniques can take up to 40 minutes to rollover to flat (and surprise surprise halving this value caused the rollover to take half the time - only 20 minutes) - so I'd hate to see
your rollover time increase by a factor of 30 !

I suggest you test it first before taking the plunge.


HTH,

David Rittenhouse
Senior Consultant, Database and Cloud Technology Services
SAP (UK) Ltd, Objects House, Vanwall Business Park, Vanwall Road, Maidenhead, Berkshire, SL6 4UB

E:  d.rittenhouse at sap.com<mailto:d.rittenhouse at sap.com>
M: +44 (0) 7899 948 295
www.sap.com/uk
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From: iqug-bounces at iqug.org [mailto:iqug-bounces at iqug.org] On Behalf Of Henderson, William L
Sent: 11 March 2015 14:20
To: IQ Users Group
Subject: [IQUG] Sybase 16 - FP_NBIT_Autosize_Limit

Hey Guys,

I notice the default max nBIT is 20 bits, before you flip to flat FP. On IQ 15 we were pretty happy with 3 Byte FPs, so I am thinking we will change FP_NBIT_Autosize_Limit to 33554431, to allow 24 byte, but flip to flat above that. Does that make sense? Does anyone know the pros/cons?

The table I am particularly interested in has about 30 billion rows (and growing), and there are some columns which will be about 22/23 bit if I do this. These columns are used as id's and occasionally will be used as SARGS or joins, but never in group bys. We have 1.5 TB of RAM.

Thanks,
Will

________________________________
Will Henderson | Prada AD | J.P. Morgan | 15F, 25 Bank Street, Canary Wharf, London, E14 5JP | T: +44 (0)207 134 3864 | william.l.henderson at jpmorgan.com<mailto:william.l.henderson at jpmorgan.com> | jpmorgan.com<http://www.jpmorgan.com/>


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