Columnar Properties¶

Properties are stored in a columnar format for efficient access and compression.

Why Columnar?¶

Benefit	Description
Compression	Same-type values compress better
Cache efficiency	Sequential access patterns
Vectorization	SIMD-friendly operations
Selective reads	Only read needed columns

Storage Layout¶

Property Store for "Person" nodes:
┌─────────────────────────────────────────────┐
│ Column: "name" (String)                     │
├─────────────────────────────────────────────┤
│ ["Alix", "Gus", "Harm", "Dave", ...]      │
├─────────────────────────────────────────────┤
│ Column: "age" (Int64)                       │
├─────────────────────────────────────────────┤
│ [30, 25, 35, 28, ...]                       │
├─────────────────────────────────────────────┤
│ Column: "active" (Bool)                     │
├─────────────────────────────────────────────┤
│ [true, true, false, true, ...]              │
└─────────────────────────────────────────────┘

Type-Specific Storage¶

Type	Storage Format
Bool	Bit-packed array
Int64	Native array or delta-encoded
Float64	Native array
String	Dictionary + offsets
List	Nested columnar

Null Handling¶

Nulls are tracked with a validity bitmap:

Values:   [30, 25, _, 28, _, 35]
Validity: [1,  1,  0, 1,  0, 1 ]

In the Database File¶

The layout above is the one in memory. A checkpoint writes each property column as column chunks of the LPG_STORE section: per group of 65,536 node or edge ids, the column's values in chunks of at most 1 MiB. A chunk stores only the rows that have a value, behind a presence bitmap (one bit per row, left out when every row has a value), so a missing property costs one bit and is never stored as an empty value. Each chunk picks its codec from its values:

Values in the chunk	Stored as
Non-negative `Int64`	Bit-packed to the width of the largest
`Int64`, some negative	8 bytes each
`Float64`	8 bytes each, by their bits
`Bool`	1 bit each
`String`	The chunk's distinct strings once, and a 4-byte code per value
Vectors of one dimension count	4 bytes per component
Any other kind, or several kinds	Each value in a lossless tagged encoding

A typed codec is used only when every value of the chunk has its kind, so every value reads back exactly as it was written. Each chunk of numbers, booleans or short strings also stores a zone map. See Column Chunks for the byte layout.