compaction()

Composable log compaction — retains only the latest entry per key.

Signature

function compaction<V>(
	log: ReactiveLog<V>,
	keyFn: (value: V) => string,
	opts?: CompactionOptions,
): CompactionResult<V>

Parameters

Parameter	Type	Description
log	ReactiveLog<V>	The reactiveLog to compact.
keyFn	(value: V) => string	Function that extracts a dedup key from each entry value.
opts	CompactionOptions	Optional configuration.

Returns

CompactionResult<V> — compact() for manual trigger, destroy() to stop auto-compaction.

Basic Usage

import { reactiveLog } from 'callbag-recharge/data';
import { compaction } from 'callbag-recharge/data';

const log = reactiveLog<{ id: string; v: number }>();
const c = compaction(log, e => e.id);
log.append({ id: "a", v: 1 });
log.append({ id: "b", v: 2 });
log.append({ id: "a", v: 3 });
c.compact(); // removes first "a" entry, keeps { id: "a", v: 3 } and { id: "b", v: 2 }

Options / Behavior Details

• Composable: Does not modify the ReactiveLog interface. Attaches externally and operates on the log's public API.
• Compaction semantics: For each key, only the entry with the highest sequence number is retained. All older entries for that key are discarded.
• Implementation: Reads all entries via toArray(), deduplicates, then clear() + appendMany() to rebuild. Sequence numbers are reassigned (compaction is a structural rewrite).
• Auto-trigger: Set threshold to auto-compact when entry count reaches the threshold. Checked on every append event.