Module write_engine 

Write engine for SSTable generation and persistence (M5)

This module provides the write path for CQLite, implementing WAL-backed memtable flushing and K-way merge for producing valid Cassandra 5.0 SSTables.

Architecture

The WriteEngine is the public API that coordinates:

1. WAL (Write-Ahead Log) - Durability
2. Memtable - In-memory buffer
3. SSTableWriter - On-disk persistence

Write Flow

1. User calls write(mutation) or execute(cql_statement)
2. WriteEngine appends to WAL (durability)
3. WriteEngine inserts into Memtable
4. When Memtable exceeds threshold → flush to SSTable
5. After successful flush → truncate WAL

Recovery

On startup, the WriteEngine replays WAL entries into the memtable.

Re-exports

pub use export::ExportOptions;

pub use export::ExportReport;

pub use memtable::Memtable;

pub use merge::KWayMerger;

pub use merge_policy::STCSPolicy;

pub use mutation::CellOperation;

pub use mutation::ClusteringBound;

pub use mutation::ClusteringKey;

pub use mutation::DecoratedKey;

pub use mutation::Mutation;

pub use mutation::PartitionKey;

pub use mutation::PartitionTombstone;

pub use mutation::RangeTombstone;

pub use mutation::TableId;

pub use wal::WriteAheadLog;

Modules

cql_to_mutation

CQL AST to Mutation conversion.

export

SSTable export functionality for M5.2 (Issue #388)

memtable

In-memory write buffer (memtable)

merge

K-way merge for combining multiple L0 SSTables

merge_policy

Compaction merge policies for SSTable selection (M5.2)

mutation

Mutation types for CQL write operations

wal

Write-ahead log (WAL) for crash recovery

Structs

CompactionStats

Cumulative statistics across all compaction operations (M5.2, Issue #474)

MaintenanceReport

Maintenance report from a maintenance_step() call (M5.2, Issue #384)

WriteEngine

Write engine coordinator

WriteEngineConfig

Write engine configuration

Enums

Durability

WAL durability mode for the write engine.

Traits

MergePolicy

Trait for merge policy implementations (M5.2, Issue #383)