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changes.mady.by.user Taras Ledkov

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changes.mady.by.user Taras Ledkov

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Field

Size

Comments
Schema version2 bytes.

short number. The possible values are:

  • positive - regular row: key  and value chunks are present;
  • 0 - no value. If the flag is set, the value chunk is omitted, e.g. the row represents a tombstone or key-row to lookup by the key;
  • negative - invalid schema version.
Key columns hash4 bytes
Key chunk:

Key chunk size
4 bytes
Flags1 byte
Variable-length columns offsets table size0-2 or 0 bytes
  • Vartable is skipped (zero size) when the chunk contains one varlen column or doesn't contain varlen column.
  • 1 byte size for table with TINY format (see table below)
  • 2 bytes for table with MEDIUM and LARGE format (see table below)
Variable-length columns offsets tableVariable (number of non-null varlen columns * <format_size>)<format_size> - depends on the Flags field. See the table below
Fix-sized columns valuesVariable
Variable-length columns valuesVariable
Value chunk:

Value chunk size4 bytes
Flags1 byte
Null-map

(number of columns / 8 ) or 0 bytes

Zero size if and only if schema has no nullable columns
Variable-length  columns offsets table size2 or 0 bytes
  • Vartable is skipped (zero size) when the chunk contains one varlen column or doesn't contain varlen column.
  • 1 byte size for table with TINY format (see table below)
  • 2 bytes for table with MEDIUM and LARGE format (see table below)
Variable-length  columns offsets tableVariable (number of non-null varlen columns * <format_size>)<format_size> - depends on the Flags field. See the table below
Fix-sized columns valuesVariable
Variable-length columns valuesVariable

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The flags field is used to detect the format. We propose 3 formats for a vartable: tiny, medium, and large with offset fields sizes of byte, short, and int respectively.
Vartable length field is the size of byte for tiny format and the size of short for others. .
Vertable length is calculated as: <count_of _not_null_varlen_fields> - 1. The offset for the first varlen field is not stored at the table. It is calculated as the begin of the varlen values block.

IMPORTANT: having multiple formats MUST guarantee the key (as well as value) chunk will be always written in a single possible way to allow comparing chunks of rows of the same version as just byte arrays.

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