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Message Posted: Thu, 12 Sep 2002 @ 14:12:16 GMT

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Each row needs a bit to say the column is compressed. Sometimes, when adding a column or two, there might already be room in the existing bit array, because the bit array has to be rounded up to the nearest byte.

In your case, where you are adding 15 columns, you definitely need two extra bytes per row for the compress bits, and maybe two bytes per row for the null bit (not sure if it stores this for not-null columns).

So the new table definitely needs to be larger than the old.

To tell if the compress is really working, you would need to decide if the extra size of the table is just from the extra bytes to store the compress bits, or it is enough extra space to store the blanks, which would vary depending on the datatype of the column. if the column is CHAR(1), you'd need a byte per column to actually store the data (plus the bytes for the compress bits). If VARCHAR(x), you'd need 3 bytes per column.

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