Make LRU doubly-linked list
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c37cb3df83
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2 changed files with 250 additions and 23 deletions
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@ -59,4 +59,181 @@ describe("fixedSizeDocumentCache", () => {
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cache.put(1, doc1);
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assert.equal(cache.get(1), undefined);
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});
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it("multipleEvictionsInSinglePut", async () => {
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const cache = new FixedSizeDocumentCache(10);
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const doc1 = new Uint8Array([1, 2]);
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const doc2 = new Uint8Array([3, 4]);
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const doc3 = new Uint8Array([5, 6]);
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const doc4 = new Uint8Array([7, 8, 9, 10, 11, 12, 13, 14]); // 8 bytes
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cache.put(1, doc1);
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cache.put(2, doc2);
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cache.put(3, doc3);
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// Cache now has 6 bytes total
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cache.put(4, doc4); // Should evict doc1 and doc2 to make room (total: 2+8=10)
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assert.equal(cache.get(1), undefined); // Evicted
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assert.equal(cache.get(2), undefined); // Evicted
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assert.equal(cache.get(3), doc3); // Still present
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assert.equal(cache.get(4), doc4);
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});
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it("clearCache", async () => {
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const cache = new FixedSizeDocumentCache(10);
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const doc1 = new Uint8Array([1, 2]);
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const doc2 = new Uint8Array([3, 4]);
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cache.put(1, doc1);
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cache.put(2, doc2);
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assert.equal(cache.get(1), doc1);
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assert.equal(cache.get(2), doc2);
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cache.clear();
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assert.equal(cache.get(1), undefined);
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assert.equal(cache.get(2), undefined);
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// Should be able to add entries after clear
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cache.put(3, doc1);
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assert.equal(cache.get(3), doc1);
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});
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it("getNonExistentKey", async () => {
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const cache = new FixedSizeDocumentCache(10);
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const doc1 = new Uint8Array([1, 2]);
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cache.put(1, doc1);
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assert.equal(cache.get(999), undefined);
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});
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it("updateEntryWithDifferentSizeTriggeringEviction", async () => {
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const cache = new FixedSizeDocumentCache(6);
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const doc1_v1 = new Uint8Array([1, 2]);
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const doc1_v2 = new Uint8Array([1, 2, 3, 4]); // Larger version
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const doc2 = new Uint8Array([5, 6]);
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const doc3 = new Uint8Array([7, 8]);
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cache.put(1, doc1_v1);
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cache.put(2, doc2);
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cache.put(3, doc3);
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// Update doc1 with larger version, should evict doc2
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cache.put(1, doc1_v2);
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assert.equal(cache.get(1), doc1_v2);
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assert.equal(cache.get(2), undefined); // Evicted
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assert.equal(cache.get(3), doc3);
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});
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it("singleItemCache", async () => {
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const cache = new FixedSizeDocumentCache(2);
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const doc1 = new Uint8Array([1, 2]);
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const doc2 = new Uint8Array([3, 4]);
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cache.put(1, doc1);
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assert.equal(cache.get(1), doc1);
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cache.put(2, doc2);
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assert.equal(cache.get(1), undefined); // Evicted
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assert.equal(cache.get(2), doc2);
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});
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it("multipleGetsOnSameEntry", async () => {
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const cache = new FixedSizeDocumentCache(4);
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const doc1 = new Uint8Array([1, 2]);
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const doc2 = new Uint8Array([3, 4]);
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const doc3 = new Uint8Array([5, 6]);
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cache.put(1, doc1);
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cache.put(2, doc2);
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// Multiple gets on doc1
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cache.get(1);
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cache.get(1);
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cache.get(1);
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// Order should be: 2 (LRU), 1 (MRU)
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cache.put(3, doc3);
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assert.equal(cache.get(1), doc1);
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assert.equal(cache.get(2), undefined); // Evicted
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assert.equal(cache.get(3), doc3);
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});
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it("exactlySizedEntry", async () => {
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const cache = new FixedSizeDocumentCache(4);
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const doc1 = new Uint8Array([1, 2, 3, 4]); // Exactly cache size
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cache.put(1, doc1);
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assert.equal(cache.get(1), doc1);
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const doc2 = new Uint8Array([5, 6]);
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cache.put(2, doc2);
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// doc1 should be evicted to make room for doc2
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assert.equal(cache.get(1), undefined);
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assert.equal(cache.get(2), doc2);
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});
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it("updateEntryMakesItMostRecent", async () => {
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const cache = new FixedSizeDocumentCache(6);
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const doc1_v1 = new Uint8Array([1, 2]);
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const doc1_v2 = new Uint8Array([3, 4]);
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const doc2 = new Uint8Array([5, 6]);
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const doc3 = new Uint8Array([7, 8]);
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const doc4 = new Uint8Array([9, 10]);
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cache.put(1, doc1_v1);
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cache.put(2, doc2);
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cache.put(3, doc3);
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// Update doc1 (should move it to most recent)
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cache.put(1, doc1_v2);
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// Order should be: 2 (LRU), 3, 1 (MRU)
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// Adding doc4 should evict doc2
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cache.put(4, doc4);
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assert.equal(cache.get(1), doc1_v2);
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assert.equal(cache.get(2), undefined); // Evicted
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assert.equal(cache.get(3), doc3);
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assert.equal(cache.get(4), doc4);
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});
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it("alternatingAccessPattern", async () => {
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const cache = new FixedSizeDocumentCache(4);
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const doc1 = new Uint8Array([1, 2]);
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const doc2 = new Uint8Array([3, 4]);
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const doc3 = new Uint8Array([5, 6]);
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cache.put(1, doc1);
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cache.put(2, doc2);
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// Alternate access between doc1 and doc2
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cache.get(1);
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cache.get(2);
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cache.get(1);
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cache.get(2);
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// Order should be: 1, 2 (MRU)
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cache.put(3, doc3);
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assert.equal(cache.get(1), undefined); // Evicted
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assert.equal(cache.get(2), doc2);
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assert.equal(cache.get(3), doc3);
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});
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it("zeroByteDocs", async () => {
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const cache = new FixedSizeDocumentCache(2);
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const doc1 = new Uint8Array([]);
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const doc2 = new Uint8Array([]);
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const doc3 = new Uint8Array([1, 2]);
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cache.put(1, doc1);
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cache.put(2, doc2);
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cache.put(3, doc3);
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assert.equal(cache.get(1), doc1);
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assert.equal(cache.get(2), doc2);
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assert.equal(cache.get(3), doc3);
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});
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});
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@ -2,27 +2,39 @@
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import type { VaultUpdateId } from "../persistence/database";
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// Doubly-linked list node for O(1) LRU operations
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class LRUNode {
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public constructor(
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public key: VaultUpdateId,
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public value: Uint8Array,
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public prev: LRUNode | null = null,
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public next: LRUNode | null = null
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) {}
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}
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// evicting the least recently used documents when the size limit is exceeded.
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export class FixedSizeDocumentCache {
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private readonly maxSizeInBytes: number;
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private currentSizeInBytes: number;
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private readonly cache: Map<VaultUpdateId, Uint8Array>;
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private usageOrder: VaultUpdateId[];
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private readonly cache: Map<VaultUpdateId, LRUNode>;
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private head: LRUNode | null; // Least recently used
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private tail: LRUNode | null; // Most recently used
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public constructor(maxSizeInBytes: number) {
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this.maxSizeInBytes = maxSizeInBytes;
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this.currentSizeInBytes = 0;
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this.cache = new Map();
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this.usageOrder = [];
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this.head = null;
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this.tail = null;
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}
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public get(updateId: VaultUpdateId): Uint8Array | undefined {
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const entry = this.cache.get(updateId);
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if (entry) {
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this.usageOrder = this.usageOrder.filter((id) => id !== updateId);
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this.usageOrder.push(updateId);
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return entry;
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const node = this.cache.get(updateId);
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if (node) {
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this.moveToTail(node);
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return node.value;
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}
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return undefined;
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}
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@ -33,31 +45,69 @@ export class FixedSizeDocumentCache {
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}
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// If the document is already in the cache, update it
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const existingEntry = this.cache.get(updateId);
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if (existingEntry != null) {
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this.currentSizeInBytes -= existingEntry.byteLength;
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const existingNode = this.cache.get(updateId);
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if (existingNode != null) {
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this.currentSizeInBytes -= existingNode.value.byteLength;
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this.removeNode(existingNode);
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this.cache.delete(updateId);
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this.usageOrder = this.usageOrder.filter((id) => id !== updateId);
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}
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this.cache.set(updateId, content);
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this.usageOrder.push(updateId);
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const newNode = new LRUNode(updateId, content);
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this.cache.set(updateId, newNode);
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this.addToTail(newNode);
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this.currentSizeInBytes += content.byteLength;
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// Evict least recently used documents if over size limit
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while (
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this.currentSizeInBytes > this.maxSizeInBytes &&
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this.usageOrder.length > 0
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) {
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const lruUpdateId = this.usageOrder.shift()!; // eslint-disable-line @typescript-eslint/no-non-null-assertion
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const lruEntry = this.cache.get(lruUpdateId)!; // eslint-disable-line @typescript-eslint/no-non-null-assertion
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this.cache.delete(lruUpdateId);
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this.currentSizeInBytes -= lruEntry.byteLength;
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while (this.currentSizeInBytes > this.maxSizeInBytes && this.head) {
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const lruNode = this.head;
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this.removeNode(lruNode);
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this.cache.delete(lruNode.key);
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this.currentSizeInBytes -= lruNode.value.byteLength;
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}
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}
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public clear(): void {
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this.cache.clear();
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this.usageOrder = [];
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this.head = null;
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this.tail = null;
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this.currentSizeInBytes = 0;
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}
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private removeNode(node: LRUNode): void {
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if (node.prev) {
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node.prev.next = node.next;
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} else {
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this.head = node.next;
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}
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if (node.next) {
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node.next.prev = node.prev;
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} else {
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this.tail = node.prev;
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}
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node.prev = null;
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node.next = null;
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}
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private addToTail(node: LRUNode): void {
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node.prev = this.tail;
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node.next = null;
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if (this.tail) {
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this.tail.next = node;
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}
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this.tail = node;
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this.head ??= node;
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}
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private moveToTail(node: LRUNode): void {
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if (node === this.tail) {
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return;
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}
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this.removeNode(node);
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this.addToTail(node);
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}
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}
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