Continuous NBit dictionary compression replaces 1, 2, 3 byte dictionary compression in the initial 16.0 version. All datatypes except LOB (character and binary) and BIT datatypes may be NBit columns.
NBit dictionary compression provides more efficient compression and greater performance than 1, 2, 3 byte dictionary compression. The IQ UNIQUE column constraint explicitly determines whether the column loads as Flat FP or NBit FP. An IQ UNIQUE n value set to 0 specifies a Flat FP. An n value greater than 0 but less than FP_NBIT_AUTOSIZE_LIMIT creates a NBit column initially sized to n.
Columns without an IQ UNIQUE constraint implicitly load as NBit up to the limits defined in the FP_NBIT_AUTOSIZE_LIMIT. Use IQ UNIQUE in cases where you want to load the column as Flat FP or when you want to load a column as NBit when the number of distinct values exceeds the auto-size limit.
NBit Value | IQ UNIQUE |
---|---|
1 |
2 |
2 |
4 |
3 |
8 |
4 |
16 |
5 |
32 |
6 |
64 |
7 |
128 |
8 |
256 1 |
9 |
512 |
10 |
1024 |
11 |
2048 |
12 |
4096 |
13 |
8192 |
14 |
16384 |
15 |
32768 |
16 |
65536 2 |
17 |
131972 |
18 |
262144 |
19 |
524288 |
20 |
1048576 |
21 |
2097152 |
22 |
4194304 |
23 |
8388608 |
24 |
16777216 3 |
25 |
33554432 |
26 |
67108864 |
27 |
134217728 |
28 |
268435456 |
29 |
536870912 |
30 |
1073741824 |
31 |
2147483647 |
1 Equivalent to FP(1) 2 Equivalent to FP(2) 3 Equivalent to FP(3) |
See these topics in the SAP Sybase IQ documentation: