Changes between Version 14 and Version 15 of dbSchemaUpdateApr09


Ignore:
Timestamp:
05/14/2009 03:53:44 AM (11 years ago)
Author:
jbecla
Comment:

added some notes on sizes

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  • dbSchemaUpdateApr09

    v14 v15  
    22 
    33This document captures proposed changes to the key LSST Database tables (Object, Source, !FaintSource, DIASource) to make these tables aligned with the Level 1 and Level 2 data products outlined in the document written for Science Collaboration after the FRS meeting at UC Davis. 
     4 
     5== Sizes == 
     6 
     7This schema is still "under construction", but the following can already give a useful perspective: 
     8 
     9If we assume 250 bytes for Object table (rough estimate based on the proposed schema below), 200 bytes for Source (rough estimate) and 24 bytes for !FaintSource, and run these numbers through the storage estimates spreadsheet, we are getting: 
     10 
     11 * !FaintSource table = 61% 
     12 * Source = 33%, and 
     13 * Object = 0.5% 
     14of the total database size. 
     15 
     16So: 
     17 * optimizing size of the Object table is not making much difference (it still may for the disk IO depending on access patterns) 
     18 * we are paying huge price for introducing the !FaintSource, every byte added here adds over a petabyte to the final size of the database. 
     19 * understanding access patterns for !FaintSource and Source is becoming extremely important. Avoiding joins with !FaintSource and Source at all cost by pushing summary information into the lightweight Object table is the way to go. 
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