Module descriptor 

Database column descriptors

Templates classifying column families along three axes:

• Write pattern: RANDOM (writes scatter across the keyspace) vs SEQUENTIAL (writes append to the end). Drives compaction priority (OldestSmallestSeqFirst vs OldestLargestSeqFirst) and write-buffer sizing.
• Dataset size: plain (level compaction, MB-scale files) vs _SMALL (universal compaction, KB-scale files and blocks).
• Retention: plain (unbounded) vs _CACHE (FIFO eviction bounded by limit_size and ttl).

Each CF in maps::MAPS picks one template and overrides individual knobs as needed.

Structs

Descriptor 🔒

Column Descriptor

Enums

CacheDisp 🔒

Cache Disposition

Statics

BASE 🔒

Base descriptor supplying common defaults to all derived descriptors.

DROPPED 🔒

Tombstone descriptor for columns which have been or will be deleted. Descriptors of this kind are explicitly set to delete data. Care should be taken when using this as it inhibits downgrading and other migrations.

IGNORED 🔒

Placeholder descriptor for existing columns which have no description. Automatically generated on db open; should not appear in any schema.

RANDOM 🔒

Descriptor for large datasets where writes scatter across the keyspace.

RANDOM_CACHE 🔒

Descriptor for large persistent caches where writes scatter across the keyspace. Oldest entries are evicted by FIFO compaction once limit_size is reached.

RANDOM_SMALL 🔒

Descriptor for small datasets where writes scatter across the keyspace.

RANDOM_SMALL_CACHE 🔒

Descriptor for small persistent caches where writes scatter across the keyspace. Oldest entries are evicted by FIFO compaction once limit_size is reached.

SEQUENTIAL 🔒

Descriptor for large datasets where writes append to the end of the keyspace.

SEQUENTIAL_CACHE 🔒

Descriptor for large persistent ring/queue caches where writes append to the end of the keyspace. Lowest keys are evicted off the front once limit_size is reached.

SEQUENTIAL_SMALL 🔒

Descriptor for small datasets where writes append to the end of the keyspace.

SEQUENTIAL_SMALL_CACHE 🔒

Descriptor for small persistent ring/queue caches where writes append to the end of the keyspace. Lowest keys are evicted off the front once limit_size is reached.