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The documentation recommends not to compress columns with less than 130 chars. Anyway the sa_column_stats procedure has a value num_values_compressed. So there seems to be a mechanism which prevents to compress rows which have a value of less than 130 chars and still compress rows with values where compression would be beneficial. Is this correct? |
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question asked: 09 Sep '10, 09:58
question was seen: 2,446 times
last updated: 09 Sep '10, 14:43
Which version do you use? AFAIK, there have been relevant changes w.r.t. column compression (in V10, I think). The CREATE TABLE statement has the INLINE and PREFIX clauses for this, cf. http://dcx.sybase.com/index.html#1200en/dbreference/create-table-statement.htm
Oh, I wasn't aware of the changes, the version I am referring to is 11.0.1 Will the default for prefix mean that everything > 8 Bytes will be compressed? Or is there still an additional margin, because the compression overhead is said to be at least 12 Bytes...
@Volker: The INLINE and PREFIX values affect how a blob is stored (inline with the rest of the row or separately in a blob page). AFAIK they have nothing to do with COMPRESSED.
From the documentation it seems, that at least prefix is also affecting compression: The prefix data for a compressed column is stored uncompressed, so if all the data required to satisfy a request is stored in the prefix, no decompression is necessary