Get the total number (size) of the LevelDB keys

[huan]

Current we are using a for loop to loop all keys to count:

flash-store/src/flash-store.ts

Lines 213 to 223 in 6b500cb

	public get size (): Promise<number> {
	log.verbose('FlashStore', 'size()')
	/* eslint no-async-promise-executor: 0 */
	// TODO: is there a better way to count all items from the db?
	return new Promise<number>(async (resolve, reject) => {
	try {
	let count = 0
	for await (const _ of this) {
	count++
	}

Related links:

• SO: How to get the exact number of keys in leveldb fast?
• memory allocated for default env is not deallocated google/leveldb#113