I'm new to redis, have doubt on below commands
In redis-cli i have entered info keyspace, for this i got the following output
# Keyspace
db0:keys=2,expires=0,avg_ttl=0
What does the above lines represent. N how to get the value from key.
You might want to look at https://redis.io/commands/INFO
To be specific the keyspace is, as mention in the official doc:
Database related statistics
The keyspace section provides statistics on the main dictionary of each database. The statistics are the number of keys, and the number of keys with an expiration.
For each database, the following line is added:
dbXXX: keys=XXX,expires=XXX
So in your case you have 2 keys present in redis
Related
Is it possible to retrieve all LFU keys from Redis database? If yes, please advice with a sample command-line.
Thanks a million,
Mughrabi
You can use OBJECT IDLETIME to get the number of seconds for which a key is not requested by a read or write operation. Then sort the idletimes for all keys to find LFU keys. Redis doesn't ship with a command which can print LFU keys as such. You probably have to write a script to do this.
https://redis.io/commands/OBJECT
I have keys I want to keep indefinitely in redis provided I have enough memory. However, if redis runs low on memory, then I'd like it to remove the oldest keys first. I looked at the "eviction policy" options and it appears redis doesn't support this out of the box. https://support.redislabs.com/hc/en-us/articles/203290657-What-eviction-policies-do-you-support-
How could I implement this myself using commands available as part of the redis-client api?
Here's some pseudocode that might work to give a flavor for what I need:
1. Get the first N keys from a list sorted by key date asc.
2. Delete the oldest keys.
3. Repeat until memory is no longer constrained.
The eviction policy determines what happens when a database reaches its memory limit. To make room for new data, older data is evicted (removed) according to the selected policy.
You can select the policies from the reference link below based on your requirement. The one I am using in the example below is "allkeys-lru"
reference link
Example -
127.0.0.1:6379> CONFIG SET maxmemory-policy allkeys-lru
OK
Example in Python -
import redis
client = redis.Redis(host='localhost', port=6379, db=0)
client.config_set('maxmemory-policy', "allkeys-lru")
I am new to redis, I do not know the meaning of "keyspace" and "key space" in redis terminology which I encountered in redis official website. Can someone help me to clear that? Thanks.
These terms refer to the internal dictionary that Redis manages, in which all keys are stored. The keyspace of a Redis database is managed by a single server in the case of a single instance deployment, and is divided to exclusive slot ranges managed by different nodes when using cluster mode.
In a key-value database, all keys can be in one node or divided in multiple nodes. Suppose I am storing telephone dictionary as key-value store with name as key and phone number as a value. If I store names A-L on one node and M-Z on another node, I divide my database into two key spaces. When I run query to search number of Smith, I need to search only second key space or node. This divides the query on multiple nodes and divide the work giving faster result. This could be shared-nothing model of working.
I'm have hashes in redis cache like:
Hash Key Value
hashme:1 Hello World
hashme:2 Here Iam
myhash:1 Next One
My goal is to get the Hashes as output in the CLI like:
hashme
myhash
If there's no such option, this is ok too:
hashme:1
hashme:2
myhash:1
I didn't find any relevant command for it in Redis API.
Any suggestions ?
You can use the SCAN command to get all keys from Redis. Then for each key, use the TYPE command to check if it's a hash.
UPDATE:
With Redis 6.0, the SCAN command supports TYPE subcommand, and you can use this subcommand to scan all keys of a specified type:
SCAN 0 TYPE hash
Also never use KEYS command in production environment!!! It's a dangerous command which might block Redis for a long time.
keys *
is work for me. you Can try it.
The idea of redis (and others K/v stores) is for you to build an index. The database won't do it for you. It's a major difference with relational databases, which conributes to better performances.
So when your app creates a hash, put its key into a SET. When your app deletes a hash, remove its key from the SET. And then to get the list of hash IDs, just use SMEMBERS to get the content of the SET.
connection.keys('*') this will bring all the keys irrespective of the data type as everything in redis is stored as key value format
for redis in python, you can use below command to retrieve keys from redis db
def standardize_list(bytelist):
return [x.decode('utf-8') for x in bytelist]
>>> standardize_list(r.keys())
['hat:1236154736', 'hat:56854717', 'hat:1326692461']
here r variable is redis connection object
My problem is: i have a set of values that each of them has to have an expire value.
code:
set a:11111:22222 someValue
expire a:11111:22222 604800 \\usually equal a week
In a perfect world i would have put all those values in a hash and give each of them it's appropriate expire value, but redis does not allow expire on a hash fields.
problem is that i also have a process that need to get all those keys about once an hour
keys a:*
this command is really expensive and according to redis documentation can cause performance issues. I have about 25000-30000 keys at each given moment.
Does someone knows how can i solve such a problem?
thumbs up it guarantee (-;
Roy
Let me propose an alternative solution.
Rather than asking Redis to scan all the keys, why not perform a background dump, and parse the dump to extract the keys? This way, there is zero impact on the Redis instance itself.
Parsing the dump file is not as scary as it sounds, because you can use the excellent redis-rdb-tools package:
https://github.com/sripathikrishnan/redis-rdb-tools
You can either convert the dump file into a json file, and then parse the json file, or use the Python API to extract the keys by yourself.
As you've already mentioned, using keys is not a good solution to get your keys:
Warning: consider KEYS as a command that should only be used in production environments with extreme care. It may ruin performance when it is executed against large databases. This command is intended for debugging and special operations, such as changing your keyspace layout. 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 sets.
Source: Redis docs for KEYS
As the docs are suggesting, you should build your own indices!
A common way of building an index is to use a sorted set. You can read more on how it's working on my question over here.
Building references to your a:* keys using a sorted set, will also allow you to only select the required keys in relation to a date or any other int value, in case you're filtering the results!
And yes: it would be awesome if hashes could expire. Sadly it looks like its not going to happen, but there are in fact creative alternatives to take care about it by yourself.
Why don't you use a sorted set.
Here is some data creation sequence.
redis 127.0.0.1:6379> setex a:11111:22222 604800 someValue
OK
redis 127.0.0.1:6379> zadd user:index 1385112435 a:11111:22222 // 1384507635 + 604800
(integer) 1
redis 127.0.0.1:6379> setex a:11111:22223 604800 someValue2
OK
redis 127.0.0.1:6379> zadd user:index 1385113289 a:11111:22223 // 1384508489 + 604800
(integer) 1
redis 127.0.0.1:6379> zrangebyscore user:index 1385112435 1385113289
1) "a:11111:22222"
2) "a:11111:22223"
This is no select performance issue.
but, It spends more memory and insert cost.