Struct KWayMerger 

pub struct KWayMerger { /* private fields */ }

K-way merger for combining multiple SSTables

Uses a min-heap to efficiently merge k sorted SSTable runs into a single output. Each run maintains a small peek buffer for efficient lookahead.

Usage

// Create merger from input SSTable paths
let merger = KWayMerger::new(input_paths, &schema)?;

// Option 1: Full merge to output writer
let stats = merger.merge(&mut output_writer)?;

// Option 2: Incremental merge (step-by-step)
loop {
    match merger.step()? {
        MergeStep::Partition { key, rows } => {
            // Process partition
        }
        MergeStep::Complete => break,
    }
}

Implementations

impl KWayMerger

pub fn new(input_paths: Vec<PathBuf>, schema: &TableSchema) -> Result<Self>

Create a new k-way merger from input SSTable paths

Arguments

• input_paths - Paths to input SSTable Data.db files (ordered newest to oldest)
• schema - Table schema for schema-aware merging

Returns

A new KWayMerger ready to merge the input SSTables.

Errors

Returns an error if any input SSTable cannot be opened.

Example

let input_paths = vec![
    PathBuf::from("data/nb-1-big-Data.db"),
    PathBuf::from("data/nb-2-big-Data.db"),
];
let merger = KWayMerger::new(input_paths, &schema)?;

pub fn merge(self, output_writer: &mut SSTableWriter) -> Result<MergeStats>

Perform a full merge to the output writer

This is a convenience method that repeatedly calls step() until the merge is complete, writing each partition to the output writer.

Arguments

• output_writer - SSTableWriter to write merged output

Returns

Statistics about the merge operation.

Errors

Returns an error if reading or writing fails.

pub fn step(&mut self) -> Result<MergeStep>

Perform one merge step (one partition)

Returns the next merged partition, or Complete if the merge is done. This allows incremental merging for better memory control.

Returns

• MergeStep::Partition - Next merged partition with all its rows
• MergeStep::Complete - Merge is complete

Errors

Returns an error if reading fails.

Trait Implementations

impl Debug for KWayMerger

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.