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Message Posted: Thu, 08 Nov 2007 @ 11:29:47 GMT

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Subj:   Re: Calculating number of compressible values as a
From:   Victor Sokovin

  The above information from the manual is a bit confusing because:  

  a) Is 8192 characters the only absolute cut-off point I should worry about? In other words, is this the only real constraint I should use to calculate how many values I could compress without running into systems limits?  

Table header may be used to store information on other things such as partitioning so all limits provided in the manuals are conditional. You should understand them as an absolute possible maximum which you can achieve when all other factors are excluded.

  b) Under which conditions would you get a thin header vs a fat header?  

This terminology sounds new to me but I think your DB release determines which type you get. Older releases tend to be thin, new releases are fat.

  d) Are MVC values stored as varying length values in the table header, or is the datatype&size of the compressed column used here?(i.e. padded with spaces).  

Not sure here. I think they may be stored exactly like you specify them in the DDL but this is worth checking.

  e) Does UNICODE/2-byte char columns have a different impact on the amount of header space used than LATIN/1-byte character columns?  

Well, yes, it uses 2 bytes per char.

  In other words, are these 8192 character positions, or 8192 Bytes?  

Bytes, so Unicode fills them up much faster than Latin.



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