Draft: Namespaces

[ederuiter]

This is an proof of concept implementation for namespaces to provide multi-tenancy support (see issue #286 / https://community.keydb.dev/t/multi-tenancy-support/78 )

Background:

We are currently running separate redis instances for each website/application we host on our kubernetes clusters (>100 sites). Most of these sites are have a fairly low volume of traffic.
This is sub-optimal for several reasons:

• extra number of pods
• memory usage
• currently no HA setup for all websites as this would increase the number of pods + memory significantly

I did a POC where I implemented the functionality in a proxy; this was based on key prefixes. but it is quite hard to make that transparent to the applications.

So I started looking into implementing this functionality in KeyDB itself; without relying on key prefixes. This would mean a different set of databases for each user. As far as I (google) could tell redis seems to scale pretty good up to 1000 databases .. as most applications only need 1 or 2 redis databases, this would mean supporting at least 100 users seems attainable.

note: Please be gentle; this is one of my first things I have done in C/C++ in a very long time.

Implementation:

The idea is simple; each user has an associated namespace. Users still see databases 0 .. <max db's>, however that are virtual databases; each namespace would have a different mapping to the global databases.
Allocations of those databases are done dynamically so we only need to maintain the databases that are used.

Besides databases also channels are namespaced. Instead of a global list of pubsub channels / patterns this is now maintained per namespace.

Most internal redis functionality does not need to know about namespaces. client->db still points to the current redis db. It is just that SELECT 0 will now select the virtual db 0, which can be mapped to the global database with id 10 for example.

TODO:

• improve performance of allocation
• support ::auto for as special namespace to automatically create a new unique namespace for a user
• support switching of namespaces for users with admin privileges
• move script cache to namespace
• stats/info per namespace
• add more tests
• add documentation
• remove some debugging asserts
• automatically remove mapping when a database is empty an not in use by any clients anymore
• fix race conditions in multi-master when allocating databases
• add per namespace memory limit

[JohnSully]

It’s actually a bug in our delete override that makes this unsafe. You should be able to delete a null pointer. We have a fix coming.

[ederuiter]

Ah that explains it, I came across it when debugging some random memory corruption issues and valgrind pointed to here for an invalid delete.

[JohnSully]

Hi @ederuiter

This change looks awesome and we’ll work with you to get it merged.

[VivekSainiEQ]

Hi @ederuiter,

I'm looking into merging your changes into the main branch.

[ederuiter]

@VivekSainiEQ Cool! Let me know if you need anything from me .. it has been a while since I have looked at this, but still very much interested in getting this merged

[VivekSainiEQ]

@ederuiter Sounds good! I've created another branch on the KeyDB repo and a subsequent PR in order to more effectively collaborate, found at #404. As a result, this ticket will be closed and further discussion can continue there.

In addition, we plan to merge your changes in without multimaster support as a first version, then add in a fix for the multimaster race condition at a later time.