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Index compression question |
Wed, Feb 6 2008 9:44 AM | Permanent Link |
Mark Wilsdorf | Trying to understand index compression a bit better...
I have a table with a non-Unique key on a single String field 159 characters long. Example values in this field would be: Grain Grain:Corn Grain:Corn:2007 Grain:Corn:2008 Grain:Wheat Grain:Wheat:2007 Grain:Wheat:2008 Would full compression be best here? I suppose trailing-byte compression should help, because of the large number of blank spaces at the end of each field. But will duplicate-byte compression also be a benefit? My real question: Does duplicate-byte compression compare bytes at the same position in adjacent keys, or does it compress duplicate bytes within a key? Thanks, Mark Wilsdorf Flagship Technologies, Inc. QuickBooks™ Add-Ons and Solutions You Can Use http://www.goflagship.com |
Wed, Feb 6 2008 2:10 PM | Permanent Link |
Tim Young [Elevate Software] Elevate Software, Inc. timyoung@elevatesoft.com | Mark,
<< Would full compression be best here? I suppose trailing-byte compression should help, because of the large number of blank spaces at the end of each field. But will duplicate-byte compression also be a benefit? >> Yes, absolutely. You've got a lot of duplicate data, so duplicate-byte compression will be able to extract a lot of space savings. << My real question: Does duplicate-byte compression compare bytes at the same position in adjacent keys, or does it compress duplicate bytes within a key? >> It compares the bytes at the same position starting from the absolute left position in the key. -- Tim Young Elevate Software www.elevatesoft.com |
Wed, Feb 6 2008 8:24 PM | Permanent Link |
Mark Wilsdorf | Tim,
Another question: After an Alter Table in DBSys to add compression, the .IDX file is the same size on disk, about 60 K on a small table. I suppose this has no bearing on the .IDX file size over the life of the database? (i.e., that compression should keep the file from growing as large). Thanks, Mark Wilsdorf Flagship Technologies, Inc. QuickBooks™ Add-Ons and Solutions You Can Use http://www.goflagship.com |
Thu, Feb 7 2008 2:40 AM | Permanent Link |
Roy Lambert NLH Associates Team Elevate | Mark
Try an optimise. Roy Lambert |
Thu, Feb 7 2008 8:53 AM | Permanent Link |
Mark Wilsdorf | Roy,
> Try an optimise. Ah...didn't think of that. Thanks! Mark Wilsdorf |
Thu, Feb 7 2008 1:26 PM | Permanent Link |
Tim Young [Elevate Software] Elevate Software, Inc. timyoung@elevatesoft.com | Mark,
<< After an Alter Table in DBSys to add compression, the .IDX file is the same size on disk, about 60 K on a small table. >> DBISAM does an "in-place" alter when you only modify the indexes, thus it re-uses the same space and does not get rid of any "extra space", rather putting it on the free list for later re-use. -- Tim Young Elevate Software www.elevatesoft.com |
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