THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Given a set of user-defined columns, this set is then rearranged so that fixed-sized columns go first. This sorted set of columns is used to form a row. Row layout is as follows:
| Field | Size |
|---|---|
| Schema version | 2 bytes |
| Key columns hash | 4 bytes |
| Key chunk: | |
| Key chunk size | 4 bytes |
| Flags | 1 byte |
| Variable-length columns offsets table size | 2 bytes |
| Variable-length columns offsets table | Variable (number of non-null varlen columns * 4) |
| Fix-sized columns values | Variable |
| Variable-length columns values | Variable |
| Value chunk: | |
| Value chunk size | 4 bytes |
| Flags | 1 byte |
| Null-map |
(number of columns / 8 |
) - If the value columns contains nullable column:0 bytes - otherwise | |
| Variable-length columns offsets table size | 2 bytes |
| Variable-length columns offsets table | Variable (number of non-null varlen columns * 4) |
| Fix-sized columns values | Variable |
| Variable-length columns values | Variable |
For the small rows, the metadata sizes may introduce a very noticeable overhead, so it looks reasonable to write them in a more compact way using different techniques.
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The flags field is a bitmask with each bit treated as a flag, with the following flags available (from flag 0 being the LSB to flag 7 being MSB):
| Flags Bits | Description |
|---|
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| 0 |
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| , 1 | VarTable formats:
|
| 2-7 | Reserverd |
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Hash calculation and key comparison
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