A Redis implementation for get/set/del values with lease. Described in paper Scaling Memcache at Facebook.

TLA+ specification for the algorithm:

• Blog post
• Source code

This is only a proof of concept. Not supposed to be used on any production environment.

Usage

Load scripts with ./load_scripts.sh <redis-host> <redis-port>. It will show commands to get/set/del values.

For get command, it will return (value, nil) if it can find a value for the key, or (nil, lease) if it cannot find a value.

Test

Functional test

Start a Redis instance at 127.0.0.1:6379. And a Redis cluster at 127.0.0.1:30001, 127.0.0.1:30002, 127.0.0.1:30003. (You can do it by following Redis cluster doc, section "Creating a Redis Cluster using the create-cluster script").

Then load the Redis scripts with ./load_scripts.sh <redis-host> <redis-port> to all the instances above.

Then run the following Python script to test:

python test.py

Jepsen test

The Jepsen test sets up two Redis instances, one as a cache and one as a database. It will read and update key "foo", and check if the value in cache and database is consistent.

Setup a Jepsen cluster with two worker nodes as redis-db and redis-cache. You can do it by using Docker (the files are modified based on Jepsen's Docker setup):

cd jepsen-test/docker
export JEPSEN_ROOT="/home/wangbin/hobbi_source/redis_lease"
./bin/up --dev

Then go into the Jepsen console container by running:

./bin/console

The code of this repo should be under /jepsen. Go to /jepsen/jepsen-test/jepsen.redis.lease and run all the tests:

cd /jepsen/jepsen-test/jepsen.redis.lease

Run the tests with raw Redis get/set/del, this test should fail since raw operations cannot guarantee cache consistency:

lein run test --nodes-file ./nodes --concurrency 500

Run the tests with our Redis get/set/del scripts, this test should succeed because our algorithm makes sure the cache will be consistent with database:

lein run test --nodes-file ./nodes --concurrency 500 --lease

Run the tests with our Redis get/set/del scripts, and import cache failures. This test should fail because the algorithm cannot guarantee cache consistency if error happens during write to cache:

lein run test --nodes-file ./nodes --concurrency 500 --lease --fail