场景问题

最近在做大模型的加载，加载文件的时候会解析出这个文件有多少个mesh, line, parameter, 而后都会存在一个变量中去保护这个关系:

const detailedList = {
   mesh: Array,
   line: Array,
   parameter: Array
}

这样会导致这个内存吃紧，毕竟间接存了好几 G 的数据信息。
那还有一种说法是，文件加载过去间接就渲染不就行了吗？
然而这样会导致 DC 过多, CPU吃不消。

IndexDB

应用 indexDB 来充当一个相似 内存 的性能，我把数据选择性的存在 indexDB 中，须要的时候再拿，这样会大大缓解内存压力。indexDB 相似 NOSQL，并不是 MYSQL 这种二维表构造, 取数据的速度是飞快的。

结构一个 Store

和大部分前端我的项目一样，我也结构了一个 store.

enum StoreType {
    MEMORY,
    INDEXDB
}

class Store {
    /**
     * 寄存在内存中的数据
     */
    private memory: Map<string, any>

    private readonly dbVersion: number;

    /**
     * indexDB
     */
    private db: IDBDatabase;

    private isReady: boolean;

    /**
     * 贮存的 value 多大才应用 indexDB 贮存，反之应用 map
     */
    private readonly limitForDB: number;

    /**
     * 达到贮存下限后一次性删除多少条数据
     */
    private readonly deleteCount: number;

    /**
     * 贮存下限
     */
    private readonly upperStorageLimit: number;

    constructor(dbVersion = 1, limitForDB?: number) {
        this.isReady = false
        this.dbVersion = dbVersion
        this.initIndexDB()
        this.memory = new Map()
        this.limitForDB = limitForDB || 30
        this.upperStorageLimit = 10000
        this.deleteCount = 20
    }

    set(key: string, value: any, type?: StoreType) {const intoMemory = () => {this.memory.set(key, value)
        }

        const intoIndexDB = () => {const objectStore = this.getObjectStore();
            objectStore.put({id: key, value}, key);
            this.calculationTimesAndDelete();}

        if (typeof type !== 'undefined') {type === StoreType.INDEXDB ? intoIndexDB() : intoMemory()} else {if (Store.sizeOf(value) > this.limitForDB) {
                // indexDB 加之前删除 map 中存在的 key
                this.clear(key, StoreType.MEMORY)
                intoIndexDB()} else {
                // 退出 map 之前删除 indexDB 中存在的 key
                this.clear(key, StoreType.INDEXDB)
                intoMemory()}
        }
    }

    get(key: string, type?: StoreType): Promise<any> {return new Promise((resolve, reject) => {const fromMemory = (key) => {resolve(this.memory.get(key))
            }
            const fromIndexDB = (key) => {const objectStore = this.getObjectStore();
                const index = objectStore.index("id");
                const res = index.get(key);
                res.onsuccess = (e) => {
                    // @ts-ignore
                    resolve(e.target.result.value)
                }
                res.onerror = (e) => {reject(e)
                }
            }

            if (typeof type !== 'undefined') {type === StoreType.INDEXDB ? fromIndexDB(key) : fromMemory(key)
            } else {this.memory.has(key) ? fromMemory(key) : fromIndexDB(key)
            }
        })
    }

    /**
     * 查询数据库条数
     */
    calculationTimesAndDelete() {const result = this.getObjectStore().count()
        result.onsuccess = (e) => {
            // @ts-ignore
            if (e.result > this.upperStorageLimit) {this.deleteFromPrevious()
            }
        }
    }

    /**
     * 达到阈值后删除最开始建设的数据
     * @description 避免数据收缩
     */
    deleteFromPrevious() {const objectStore = this.getObjectStore()
        const request = objectStore.openCursor();
        let count = 0
        request.onsuccess = (event) => {
            // @ts-ignore
            const cursor = event.target.result
            if (cursor) {if (count === this.deleteCount) return;
                count++;
                objectStore.delete(cursor.key)
                cursor.continue()}
        }
    }

    getObjectStore() {const transaction = this.db.transaction(["store"], "readwrite");
        return transaction.objectStore("store")
    }

    clear(key: string, type?: StoreType) {const fromMemoryDel = () => this.memory.delete(key)

        const fromIndexDBDel = () => {const objectStore = this.getObjectStore();
            objectStore.delete(key)
        }

        if (typeof type !== 'undefined') {type === StoreType.INDEXDB ? fromIndexDBDel() : fromMemoryDel()} else {this.memory.has(key) ? fromMemoryDel() : fromIndexDBDel()
        }
    }

    initIndexDB() {
        // @ts-ignore
        const indexedDB = window.indexedDB || window.webkitIndexedDB || window.mozIndexedDB || window.OIndexedDB || window.msIndexedDB
        if (!indexedDB) {alert('indexDB 被浏览器禁止!')
            throw new Error('indexDB forbidden in the browser!')
        }
        const request = indexedDB.open("elephantFiles", this.dbVersion)
        request.onerror = function () {throw new Error('Error creating/accessing IndexedDB database');
        }
        request.onsuccess = event => {
            // @ts-ignore
            this.db = event.target.result as IDBDatabase;
            this.isReady = true
        }
        request.onupgradeneeded = (event) => {console.log('database upgradeneeded!')
            // @ts-ignore
            const db = event.target.result as IDBDatabase;
            if (!db.objectStoreNames.contains('store')) {const store = db.createObjectStore('store')
                store.createIndex('id', 'id')
            }
        }
    }

    /**
     * @description 不确认是否初始化结束时 将查问赋值等操作包裹在此
     */
    ready(callback: Function) {const step = () => {if (this.isReady) {callback && callback()
                return;
            }
            window.requestAnimationFrame(step)
        }
        window.requestAnimationFrame(step)
    }

    /**
     * @description 估算字节大小, 疏忽 key 的长度, 如果是 object 只计算 value, 比 JSON.stringify 更快
     */
    static sizeOf(value): number {
        const typeSizes = {"undefined": () => 0,
            "boolean": () => 4,
            "number": () => 8,
            "string": item => 2 * item.length,
            "object": item => !item ? 0 : Object
                .keys(item)
                .reduce((total, key) => size(key) + size(item[key]) + total, 0)
        };
        const size = value => typeSizes[typeof value](value);
        return size(value)
    }
}


export {StoreType, Store}

应用

const a = new Store();
a.ready(() => {a.set('a', { k: 'dsdsdsdsdssdsd', p: [123, 'sdsdsdsdsdsdsdvvvvvvvvv'] })
  a.set('b', 123)

  a.get('b')

  a.get('a')
})

依据客户的客户端条件适当调节 limitForDB 和upperStorageLimit