feat: Tags can be stored separately in case the main redis instance u…

…ses eviction policy.

README.md

@@ -51,6 +51,25 @@ export const cache = new Cache({
   logger,
 });
 ```
+If your Redis instance uses eviction policy you need to use separate Redis instance for tags. **Tags should not be evicted!**
+
+```typescript
+// cache-with-tags.ts
+
+import Redis from 'ioredis';
+import Cache, { RedisStorageAdapter } from 'cachalot';
+import logger from './logger';
+
+const redis = new Redis(); // with eviction policy enabled
+const redisForTags = new Redis(6380);
+
+export const cache = new Cache({
+  adapter: new RedisStorageAdapter(redis),
+  tagsAdapter: new RedisStorageAdapter(redisForTags),
+  logger,
+});
+```
+
 There are three main methods of working with Cache; their behavior depends on the chosen caching strategy:
 
 `get` gets cache data

src/cache.ts

@@ -15,6 +15,7 @@ export interface CacheWithCustomStorageOptions {
 }
 export interface CacheWithBaseStorageOptions {
   adapter: StorageAdapter;
+  tagsAdapter?: StorageAdapter;
 }
 export interface ManagerConstructor<T extends BaseManager = any> {
   new(options: ManagerOptions): T;
@@ -60,6 +61,7 @@ class Cache {
     if (isBaseStorageOptions(options)) {
       this.storage = new BaseStorage({
         adapter: options.adapter,
+        tagsAdapter: options.tagsAdapter,
         prefix: options.prefix,
         hashKeys: options.hashKeys
       });

src/storages/base.spec.ts

@@ -318,4 +318,27 @@ describe('BaseStorage', () => {
     expect(value.tags).toMatchObject([{ name: 'tag' }]);
     expect(value.expiresIn).toEqual(expect.any(Number));
   });
+
+  it('uses separate adapter for tags', async() => {
+    const tag1 = { name: 'tag1', version: 1 };
+    const tagsTestInterface = {
+      internalStorage: {}
+    };
+    const tagsTestAdapter = new TestStorageAdapter(tagsTestInterface, true);
+    tagsTestInterface.internalStorage[`cache-${TAGS_VERSIONS_ALIAS}:tag1`] = tag1.version;
+    storage = new BaseStorage({
+      adapter: testAdapter,
+      tagsAdapter: tagsTestAdapter,
+      prefix: 'cache',
+      hashKeys: false,
+      expiresIn: 10000
+    });
+
+    const tags = await storage.getTags([tag1.name]);
+    expect(tags).toEqual([tag1]);
+
+    const tagV2 = { ...tag1, version: 2 };
+    await storage.setTagVersions([tagV2]);
+    await expect(storage.getTags([tag1.name])).resolves.toEqual([tagV2]);
+  });
 });

src/storages/base.ts

@@ -13,6 +13,7 @@ export const TAGS_VERSIONS_ALIAS = 'cache-tags-versions';
 
 export type BaseStorageOptions = {
   adapter: StorageAdapter;
+  tagsAdapter?: StorageAdapter;
   prefix?: string;
   hashKeys?: boolean;
   expiresIn?: number;
@@ -43,6 +44,7 @@ export type CommandFn = (...args: any[]) => any;
 export class BaseStorage implements Storage {
   constructor(options: BaseStorageOptions) {
     this.adapter = options.adapter;
+    this.tagsAdapter = options.tagsAdapter ?? options.adapter;
     this.prefix = options.prefix || '';
     this.hashKeys = options.hashKeys || false;
 
@@ -75,6 +77,12 @@ export class BaseStorage implements Storage {
    */
   private adapter: StorageAdapter;
 
+  /**
+   * Adapter for tags should be provided if your primary adapter uses eviction policy.
+   * This adapter should not use any eviction policy. Records should be deleted only by demand or expiration.
+   */
+  private readonly tagsAdapter: StorageAdapter;
+
   /**
    * Gets a record using an adapter. It is expected that the adapter returns or null (value not found)
    * or serialized StorageRecord.
@@ -94,7 +102,7 @@ export class BaseStorage implements Storage {
    */
   public async setTagVersions(tags: StorageRecordTag[]): Promise<any> {
     const values = new Map(tags.map(tag => [this.createTagKey(tag.name), `${tag.version}`]));
-    return this.adapter.mset(values);
+    return this.tagsAdapter.mset(values);
   }
 
   /**
@@ -137,7 +145,7 @@ export class BaseStorage implements Storage {
    * version.
    */
   public async getTags(tagNames: string[]): Promise<StorageRecordTag[]> {
-    const existingTags = await this.adapter.mget(tagNames.map(tagName => this.createTagKey(tagName)));
+    const existingTags = await this.tagsAdapter.mget(tagNames.map(tagName => this.createTagKey(tagName)));
 
     return tagNames.map((tagName, index) => ({
       name: tagName,