How does key/value pair eviction impact the entries in a Redis sorted set? Does the various eviction policies remove entries from sorted sets?
I want to load a SKU of a product sorted set as well as the category of the product included in the key. The value of the product will also be included in the key. I want to be able to query the set and get back a filtered result for a certain category and price range.
How do I know if entries from the sorted set have been evicted since the initial load of the product catalog data? Missing products from the sorted set could lead to incorrect search results.
Sorted sets do not expire individual entries. Either the whole sorted set is expired or evicted or the whole set stays.
For what you are looking at - you may want to try Redisearch
Related
I am really confused with redis sorted set.
Lets say I have N number of items in the sorted set. I assumed whenever I add an item, it will be sorted in the set.
If I need the lowest score item, I have to use this.
ZRANGE myitem 0 0
But why is the performance is O(log(N)). Should it not be O(1) if it is already sorted & to get the lowest score item?
https://redis.io/commands/zrange
As noted in the documentation, Redis uses a skip list to implement sorted sets. Skip lists have a lookup time of O(log n).
There are other answers here that go into more detail on the use of this data structure, see here for example.
I am looking to have a set which will store elements and that I can get the cardinality after. I noticed I could use the commands SADD or PFADD then use SCARD or PFCOUNT. What is the difference between these two? What are the advantages/disadvantages?
When using SADD, you store data in a SET.
When using PFADD, you store data in an Hyperloglog, which is a different kind of data structure.
A SET is used to store unique values, when you have to access again these values.
An HyperLogLog allows to get an approximate count of the number of unique values in the data added using PFADD. It is useful when you have a great number of distinct values and don't need to get them back. It may be used by example to get the number of unique visitors for a given day for a given page on a high traffic web site (you just add the unique visitor IDs to the HLL).
SADD and SCARD are for "Set".
PFADD and PFCOUNT are for "HyperLogLog".
Advantage of "HyperLogLog":
"HyperLogLog" takes much less memory than "Set".
This video below explains about "HyperLogLog" precisely in about 5 minutes.
https://youtu.be/UAL2dxl1fsE
I'm new to Redis and I want to use the following scheme:
key: EMPLOYEE_*ID*
value: *EMPLOYEE DATA*
I was thinking of adding a time stamp to the end of the key, but I'm not sure if that'll even help. Basically I want to be able to get a list of employees who are the most stale ie having been updated. What's the best way to accomplish this in Redis?
Keep another key with the data about employees (key names) and the update's timestamp - the best candidate for that is a Sorted Set. To maintain that key's data integrity, you'll have update it with pertinent changes whenever you update one the employees' keys.
With that data structure in place, you can easily get the keys names of the recently-updated employees with the ZRANGE command.
Have you tried to filter by expiration time? You could set the same expiration to all keys and update the expiration each time the key is updated. Then with a LUA script you could iterate through the keys and filter by expiration time. Those with smaller expiration time are those who are not updated.
This would work with some assumptions, it depends on how your system works. Also the approach is O(N) with respect to the number of employees. So if on one side you can save space, it will not scale well with the number of entries and the frequency of scan.
I am using jedis, a redis java client. I have a queue of string items. As per normal I am using lpush lpop rpush rpop for the necessary operations. But I will like to set expiry for each individual items in the queue. Is it possible?
This is not possible in redis by design for the sake of keeping redis simple and fast.
You can either store an expire value along with the string in the list, or store a separate list of expire times to let your application know if the key has expired.
There is also an alternative solution discussed here. You can store values in a sorted set with expire timestamps as scores and only select those members, whose scores are greater than certain timestamp. (This of course leaves it up to your app to clear the expired elements in a set)
We have questions based where in home page we were showing 2 list
Questions by date modified
Question have bigger views and ans count. And in this both listing if question have same views or ans count then sorting is based on date.
Previously i am directly quiring to MySQL database and fetching the values so it's easy.
But each page request hitting to MySQL it's bit expensive then start doing caching.
I started using Redis. Following is the cases when i use redis cache
Issues is On second listing i have to display questions by votes and not answered combine.
How can i stored this type of data in redis to load faster with sorting based by 2 conditions votes with time and ans count with time?
You can use sorted sets in redis. Your view or answer count can be the score. create a key based on timestamp. Sorted set method zrevrangebyscore will give you the correct order.
you can set your member of sorted set as:
'YEAR_MONTH_DATE_HOUR_MINUTE_SECONDS:question_id'
This way if you sort, questions with same score, will be returned in lexicographical order. That way question which came later will be placed higher if you use zrevrangebyscore.
You can create a hash map to map timestamp and question_id. for faster lookup
I asked a similar question, where I also purposed a solution. I want something different but it will do exactly what you want.
Redis zrevrangebyscore, sorting other than lexicographical order