Firebase database high delay after a long standby

Question

I'm currently testing Firebase on a non-production Firebase app which I am the only one who works on.

When I try to query the database to retrieve the data after there has not been any query during the last 24 hours, the query take about 8 seconds. After a query is done, the next ones would take normal amount of time (about 100ms).

This is not about caching the queries, by "next queries" I mean new queries which are not the same.

To reproduce it:

• Create a database node called users, users children are user data (first name, last name, age, gender, etc)
• Add 500,000 users to this node
• Get a user by its UID and measure the time. (It should take about 100ms)
• Wait 24 hours (I don't know the exact time, but I'm sure about 24 hours)
• Get any user by its UID and measure the time. (It should take about 8sec)
• Get any user by its UID and measure the time. (It should take about 100ms)

I want to know if this is a known issue to Firebase realtime database or not?

Answer 1

I reached Firebase support, they were able to recreate the issue and faced a wait time of about 6 seconds. Here is their answer after the investigation:

It looks like this is intended behavior. The realtime database queries work by building the index in-memory, which takes time linear to the number of nodes at that location. Once the index is built things are very fast, but the initial build can take a bit to build, especially for large locations.

If you wants the index to stay in memory on the database you should have a listener always listening for this query.

So basically the database takes a long time to process the query because of indexing the large database.

The problem can be solved by keeping a listener on the database or querying the database every few hours.

In production it is not very likely that you face this problem, because the database is being accessed by the user all the time, but if your database is not accessed all the time and you don't want the users experience that long wait time, you should utilize the discussed solution.

Answer 2

Firebase keeps recently used data in its internal cache. This cache is cleared after a few minutes.

But the exact numbers depend on how much data you're loading and how you're loading that data. Without seeing a specific setup that shows how to reproduce these numbers there really isn't much anyone can say.