redlock | Distributed locks with Redis and Python

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Distributed locks with Redis and Python

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redlock Examples and Code Snippets

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maven

Lines of Code : 34

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// 1. Create config object
Config config = new Config();
config.useClusterServers()
       // use "rediss://" for SSL connection
      .addNodeAddress("redis://127.0.0.1:7181");

// or read config from file
config = Config.fromYAML(new File("config-f

Community Discussions

Trending Discussions on redlock

Super basic questions about using RedLockFactory.CreateLockAsync()

How to choose the right value for the expiryTime parameter for RedLockFactory.CreateLockAsync() method?

Mocking Redlock.CreateAsync does not return mocked object

How to check if the function has executed completely and store completed flag in global variable in JavaScript

redis terminate called after throwing an instance of 'sw::redis::MovedError'

Distributed readers-writer lock in python

Is Redisson getLock() Safe for Distributed Lock Usage?

Lock on redis cluster

QUESTION

Super basic questions about using RedLockFactory.CreateLockAsync()

Asked 2021-Oct-14 at 11:06

The following pseudocode may be a little too boiled down, but this is more of a general question

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ANSWER

Answered 2021-Oct-10 at 22:10

I need to stop posting questions when burned out and frustrated late on Friday afternoon.

I dug into the source and test code for RedlockFactory and all of the things I originally thought were not working at all appear to be working just fine, both to read the code and to use the debugger.

My real panic came from the TransactionScope problem I mentioned in my edited original question and the problems there don't seem to have anything to do with how RedlockFactory or any other items implementing DisposeAsync work.

Source https://stackoverflow.com/questions/69503134

QUESTION

How to choose the right value for the expiryTime parameter for RedLockFactory.CreateLockAsync() method?

Asked 2021-Aug-20 at 22:34

I am using RedLock.net library for resource locking. To lock a resoruce I am using RedLockFactory.CreateLockAsync.

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ANSWER

Answered 2021-Aug-20 at 22:34

ExpiryTime determines the maximum time that a lock will be held in the case of a failure (say, the process holding the lock crashing). It also indirectly determines how often the lock is renewed while it is being held.

e.g.

If you set an expiry time of 10 minutes:

the automatic lock renewal timer will call out to redis every 5 minutes (expiry time / 2) to extend the lock
if your process crashes without releasing the lock, you will have to wait up to a maximum of 10 minutes until the key expires in redis and another process can take out a lock on the same resource

If you set an expiry time of 10 milliseconds:

the automatic lock renewal timer will call out to redis every 5 milliseconds (expiry time / 2) to extend the lock (which might be a little excessive)
if your process crashes without releasing the lock, you will have to wait up to a maximum of 10 milliseconds until the key expires in redis and another process can take out a lock on the same resource

It's a balance between how much time you're willing to wait for a lock to expire in the failure case vs how much load you put on your redis servers.

Source https://stackoverflow.com/questions/68855859

QUESTION

Mocking Redlock.CreateAsync does not return mocked object

Asked 2021-Jun-07 at 21:55

I am trying to Mock Redlock

I have the test below

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ANSWER

Answered 2021-Jun-07 at 21:55

The definition of CreateLockAsync

Source https://stackoverflow.com/questions/67870370

QUESTION

How to check if the function has executed completely and store completed flag in global variable in JavaScript

Asked 2021-Mar-25 at 06:19

When a user clicks on the Break button, it executes the Break() function inside the JS. It then calls getData() and also 2 lines of code after getData with CSS. But if you see that 2 CSS btnLock which use to hide lock.png and btnUnlock which displays unlock.png. it is not waiting for getData() to complete and these 2 CSS is getting overridden with what we have in buildTable(). So the option I am looking for is to build the datatable medTable.draw() first and then check if the Break() has completed. If so, then use these 2 CSS to hide and display.

So for that, I want to use the global boolean variable to store the status of the Break function. I mean whether it completed or not so that I can use it after medTable.draw(); to check the Break function completed.

Index

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ANSWER

Answered 2021-Mar-25 at 06:19

If you want to make sure

Source https://stackoverflow.com/questions/66791642

QUESTION

redis terminate called after throwing an instance of 'sw::redis::MovedError'

Asked 2020-Nov-24 at 09:17

I try to build a redis cluster follow this cluster-tutorial

I try to use this tutorial(RedLock) to write codeRed Lock

Got the following error ： terminate called after throwing an instance of 'sw::redis::MovedError'

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ANSWER

Answered 2020-Nov-24 at 09:17

Redlock does not work with Redis Cluster. Instead, it works with Single Redis instances. You should run your code with N dependent Redis instances, NOT a Redis Cluster.

terminate called after throwing an instance of 'sw::redis::MovedError'

Seems that you're using redis-plus-plus. You got this error, because you're trying to send commands to Redis Cluster with a Redis object.

Source https://stackoverflow.com/questions/64982136

QUESTION

Distributed readers-writer lock in python

Asked 2020-Apr-05 at 16:31

I am looking for a readers-writer lock that can be used in python in a distributed system.

So far I've found:

redlock, which is based on redis. Does not provide a readers-writer lock.
The distributed package of dask offers a lock, but again, no readers-writer lock.
kazoo, which works with Zookeeper, offers a readers-writer lock. However Zookeeper is an extremely heavy dependency, as it written in Java and therefore requires the JDK.

Is there a more lightweight alternative to kazoo / Zookeeper? Ideally a pure python solution that is nevertheless battle tested?

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ANSWER

Answered 2020-Apr-05 at 16:31

Redis is single-threaded and read/write operations are atomic; which means multiple simultaneous read/write operations will not succeed and readers and writer(s) will be obtaining access to the resource sequentially in atomic fashion. I believe this would solve your problem if the resource is kept in as one of the redis data structures. You do not need a separate reader-writer lock mechanism when using redis and python as combination where the resource is kept within redis.

Hope it helps

Source https://stackoverflow.com/questions/60821649

QUESTION

Is Redisson getLock() Safe for Distributed Lock Usage?

Asked 2020-Apr-03 at 10:36

Is Redisson's getLock() method good for a distributed use case, and how does it compare to getRedLock()?

Redisson (3.11.x) has several methods to instantiate locks:

RedissonClient.getLock()
RedissonClient.getRedLock()
others like getReadWriteLock(), getFairLock(), etc.

What algorithm does getLock() use, and is it safe for distributed usage? The documentation says:

Implements a non-fair locking so doesn't guarantees an acquire order by threads.

I am looking to compare getLock() to getRedLock(), which appears to use Redlock and is documented at the top-level of Redis' distlock page: https://redis.io/topics/distlock:

This page is an attempt to provide a more canonical algorithm to implement distributed locks with Redis. We propose an algorithm, called Redlock, which implements a DLM which we believe to be safer than the vanilla single instance approach.

...

ANSWER

Answered 2020-Apr-03 at 10:36

Is Redisson's getLock() method good for a distributed use case, and how does it compare to getRedLock()?

All Redisson locks fit for distributed use case. RedLock algorithm assumes that you have lock per master node in cluster. RedLock algorithm is proposition and unfortunately there are no feedbacks of its practice usage. Except of its analisys https://martin.kleppmann.com/2016/02/08/how-to-do-distributed-locking.html

What algorithm does getLock() use, and is it safe for distributed usage?

RLock object stored as single object in Redis. Other threads are notified through pubsub listeners if lock released. There is also lockWatchdogTimeout setting allows to define time after which lock will be forced to release if current thread is not alive.

UPDATE Since 3.12.5 version getLock() method returns Lock with improved reliability during failover. getRedLock() has been deprecated.

Source https://stackoverflow.com/questions/60573175

QUESTION

Lock on redis cluster

Asked 2020-Mar-23 at 10:24

I have a Redis cluster of 3 master nodes and each master has corresponding slave nodes. I would like to acquire a lock on the cluster to perform some write operations and then release the lock.

From what I've read is - To connect to a cluster we generally connect to one node in the cluster and perform all operations on that node which in-turn handles re-directing to other nodes in the cluster.

Is it possible to acquire lock on a Redis cluster? [P.S I am using Redisson client] From the examples in Redisson client under Multilock and redlock (https://github.com/redisson/redisson/wiki/8.-Distributed-locks-and-synchronizers), they are acquiring a lock on individual nodes.

How does Multi lock or Red lock work on a cluster?
How and what kind of lock do I use if I have a Redis cluster?
Which library (Jedis/Redisson) do I use?

Jedis also seems to have support for locking on the cluster (https://github.com/kaidul/jedis-lock).

P.S: I've read extensively on this, but I've not been able to find clear answers on locking on a cluster. Would really appreciate some help.

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ANSWER

Answered 2020-Mar-23 at 10:24

I found a solution to my question above.

As far as we are using the same key to acquire a lock across all client nodes, all the attempts to acquire the lock will go to the same node on the Redis cluster. So you can just use simple Rlock from Redisson.

See comments to this question: https://github.com/leandromoreira/redlock-rb/issues/63

Source https://stackoverflow.com/questions/60771436

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