As I know from Redis cluster tutorial, cluster has only 16384 slots (0 - 16383). The hashslots are calculated by following command: CRC16 (KEY) mod 16384. So for example CRC16 of some key equals 16385 and hash slot will be 1. For another key CRC16 equals 32769 and hash slot will be again 1. Is it cause some conflict? Or first one will be rewritten by second one?
If i understand your question, no this is not a conflict. Each key belogns to one hashsolt but each hashslot can have many keys.
CLUSTER GETKEYSINSLOT slot count: https://redis.io/commands/cluster-keyslot
Related
I want to use the affinity key with BinaryObject. I have used below code to set my affinity key but it didn't work. My Cache key is off type BinaryObject.
CacheKeyConfiguration keyConfiguration = new CacheKeyConfiguration(BinaryObject.class.getName(), affinityKeyConfig);
cfg.setKeyConfiguration(keyConfiguration);
I have used BinaryObject in key and value also. I have used bank as affinity key. I had inserted 4 records for 'SBI' and 8 'records for 'HDFC'. For node 1, it should show 4/8 on primary/backup and for node 2, it should show 8/4 on primary/backup.
But I can see records are equally distributed. If I use affinity key then data should not distributed equally.
I would like to have something like the following table in redis.
host name
back queue
stanford.edu
23
microsoft.com
17
As far as I know, the best way to implement this is to use redis hashes (with host name as key and back queue as value). However, in my use case, I also want to get the first key-value pair present in the hash map.
How can this be implemented? Are there any redis datatypes specifically for this?
In cluster mode of Redis, is a piece of data with a specific key has to be stored in a specific node, no matter what data structure the it has (e.g. List/Hash)?
For example, I have a hash map:
HMSET website google www.google.com yahoo www.yahoo.com
The key of the hash map is "website", and the hash map has data {google:www.google.com, yahoo:www.yahoo.com}. In my understanding, the hash map is stored in only one node of the cluster. It will be not efficient when the hash map is large (e.g. 400M key-value pairs in one hash map).
My question is: is there a way to automatically distribute the contents of the hash map of the same key among the cluster? For example, store pair {google:www.google.com} in node 0 and store pair {yahoo www.yahoo.com} in node 1, when the key of the hash map is still "website"?
In cluster mode of Redis, is a piece of data with a specific key has to be stored in a specific node, no matter what data structure the it has (e.g. List/Hash)?
Yes - every key is mapped to a hash slot, that a single cluster instance manages.
My question is: is there a way to automatically distribute the contents of the hash map of the same key among the cluster?
No - data is distributed between nodes at key level. A given key's data structure cannot be distributed between multiple shards. To distribute the data, you'll have to model it using more keys.
Correctly modeling your needs requires knowing what type of operations you'll be performing against your distributed "hash map" and their respective frequencies. Feel free to add this information to the question, or open a new one that is more focused on your requirements.
I have a Redis implementation with 6 nodes (3 masters 3 slaves - cluster enabled). I have load in every master an amount of keys.
So, my question is:
Is it possible to actual copy one key from 127.0.0.1:30001 to 127.0.0.1:30002?
For example lets say that my key has the name "testkey". If i copy this key from 30001 to 30002, when i want to get the key from 30001 or from 30002 the response must fetch the value of "testkey" in both calls.
No, that not how it works.
Keys in the cluster are assigned to hash slots and slots are assigned to master nodes. The keys' assignment is done by hashing their names (or the hash tag in them) so it is consistent, meaning that a given key name always hashes to the same slot.
A key can exist only once in the keyspace, but the slot it belongs to can be moved between masters. To scale reads from that key you can use the slave of the applicable master.
A good point to start understanding how the cluster works is by referring to the [tutorial](https://redis.io/topics/cluster-tutorial].
How I can find keys matching a pattern like this:
Eg:
I have some keys:
abc:parent1
abc:parent2
abc:parent1:child1
abc:parent2:child2
How can I find only
abc:parent1
abc:parent2
Keys is specifically noted as a command not to be run in production due to the way it works. What you need here is to create an index of your keys. Use a set for storing the key names of the pattern you want. When you add a new we key, add the name of it to the set. For example:
Set abc:parent1:child1 breakfast
Sadd abc:parent1:index abc:parent1
Then when you need the list:
Smembers abc:parent1:index
Will give you the list, without the penalties and problems associated with using the "evil" keys command. Additionally you would remove an entry with sremove on key deletion. You also get as a benefit the ability to know how many keys are in the index with a single call.
If you absolutely, positively, MUST avoid using an index use SCAN instead of keys. The only time you should even consider keys is if you are running a debug slave where the only process using it is your debugging process.
Command KEYS pattern
will help you for the same, if it is not a production environment. (Never use keys in production)
ex:
redis> MSET one 1 two 2 three 3 four 4
OK
redis> KEYS *o*
1) "two"
2) "one"
3) "four"
For your specific example, the below command will work:
redis 127.0.0.1:6379> keys *parent[0-9]
1) "abc:parent2"
2) "abc:parent1"
Here's the detailed description of the command.
Update: Though the suggestion above helps you get the desired output, the redis KEYS command is evil as the others mentioned. KEYS is blocking and can consume a lot of RAM while preparing the response.
Don't use KEYS in your regular application code. If you're looking for a way to find keys in a subset of your keyspace, consider using SCAN or sets.
Thanks The Real Bill and Itamar, I got a better understanding.