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Thus for integer values it is possible to keep only their significant bytes, omitting their high insignificant bytes. That is even if the original data type of a field is INTEGER and should occupy 4 bytes but the actual value is below 128 and above -129 then we can store it just as a single byte and reflect this in the offset table.

Corollary

If the number of fields is N and t is an array that stores a binary tuple we can find the answers for the following:

Does the tuple contain a nullmap?

hasNullmap = t[0] & 0b100;

How many bytes are occupied by the nullmap?

nullmapBytes = hasNullmap ? (N + 7) / 8 : 0;

How many bytes are occupied by one offset table entry?

offsetEntryBytes = 1 << (t[0] & 0b11);

How many bytes are occupied by the offset table?

offsetTableBytes = N * offsetEntryBytes;

What is offset of the value area?

valueBaseOffset = 1 + nullmapBytes + offsetTableBytes;

What is the whole tuple size?

tupleSize = valueBaseOffset + valueAreaSize

Reference Links

1. IEP-54: Schema-first Approach

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