I create Redis (v7) Sorted Sets with ZADD. Each set has multiple members. The score I use is a timestamp.
With ZRANGE I'm able to select members with scores between min and max. I want to select - based on one timestamp - one member after the timestamp and one before the timestamp.
Example (score, member) for one key:
(10, A)
(15, B)
(20, C)
I.e. SELECT 17 should give me (15, B) and (20, C).
Looks like Redis has no command to do this. What would be the most efficient way to do that?
You need two commands:
# get the one after the timestamp
zrangebyscore k (17 +inf limit 0 1
# get the one before the timestamp
zrevrangebyscore k (17 -inf limit 0 1
In order to be more efficient and atomic, wrap these two commands into a Lua script.
Related
I'm trying to get the value of the best key in a sorted set.
This is my query at the moment:
ZREVRANGEBYSCORE genre1 +inf -inf WITHSCORES LIMIT 0 1
This is an example of an add in my set:
ZADD "genre1|genre2|genre3" 3.25153 "film"
I'd like to use the query in a way like this
ZREVRANGEBYSCORE *genre1* +inf -inf WITHSCORES LIMIT 0 1
to match keys containing "...|genre1|..." and not only keys like "genre1".
Any help will be appreciated
This can be accomplished in two or three steps:
1) Use SCAN or KEYS to find the keys matching your pattern.
SCAN 0 MATCH "*genre1*"
1) "9"
2) 1) "genre1|genre2|genre3"
2) "genre1|genre4"
2) For each key, use TYPE to test if it is a Sorted Set. This is only important if you may have other genre1 keys on the db
TYPE "genre1|genre4"
zset
3) Run your ZREVRANGEBYSCORE <key> +inf -inf WITHSCORES LIMIT 0 1 for each key.
See this answer on how you can SCAN for a given type. You can modify the Lua script to include the ZREVRANGEBYSCORE and get your results atomically on a single call.
Finally, consider reviewing if storing the genre combinations is optimal in your case. You may use a sorted set per genre, and then use ZUNIONSTORE or ZINTERSTORE to get scored combinations.
I'm using Redis sorted set to implement the leaderboard of my game, where I show the user ranking in descending order. I'm stuck in a case where two or more users have the same score. So in this case, I want the higher ranking of the user who gets the score first. For example, I'm adding the following entries in Redis.
127.0.0.1:6379> zadd testing-key 5 a
(integer) 1
127.0.0.1:6379> zadd testing-key 4 b
(integer) 1
127.0.0.1:6379> zadd testing-key 5 c
(integer) 1
and when I'm querying for the rank in reverse order, I'm getting this
127.0.0.1:6379> zrevrange testing-key 0 10
1) "c"
2) "a"
3) "b"
but in my case, the ranking should be like
1) "a"
2) "c"
3) "b"
So is there any provision in Redis to give higher precedence to the entity which entered first in the set with the same score?
I found one solution to this problem. In my case, the score is an integer so I converted it into decimal and added Long.MAX_VALUE - System.nanoTime() after decimal. So the final score code will be like
double finalScore = score.(Long.MAX_VALUE - System.nanoTime());
So the final score of the player who scored first would be higher than the second one. Please let me know if you have any better solution.
If your leaderboard's scores are "small" enough, you may get away with using a combination of the score and the timestamp (e.g. 123.111455234, where 123 is the score). However, since the Sorted Set score is a double floating point, you may lose precision.
Alternatively, keep two Sorted Sets - one with each player's leaderboard score and the other with each player's score timestamp, and use both to determine the order.
Or, use a single sorted set for the leader board, encode the timestamp as part of the member and rely on lexicographical ordering.
I am interested in using Redis to check if a IP address (converted into integer) falls within a range of IPs. It is very likely that the ranges will overlap.
I have found this question/answer, although I am not able to fully understand the logic behind it.
Thank you for your help!
EDIT - Since I got a downvote (a comment to explain why would be nice), I've removed some clutter from my answer.
#DidierSpezia answer in your linked question is a good answer, but it becomes hard to maintain if you are adding/removing ranges.
However it is not trivial (and expensive) to build and maintain it.
I have an answer that is easier to maintain, but it could get slow and memory expensive to compute with many ranges as it requires cloning a set of all ranges.
You need to save all ranges twice, in two sets. The score of each range will be its border values.
Going with the sets in #DidierSpezia example:
A 2-8
B 4-6
C 2-9
D 7-10
Your two sets will be:
ZADD ranges:low 2 "2-8" 4 "4-6" 2 "2-9" 7 "7-10"
ZADD ranges:high 8 "2-8" 6 "4-6" 9 "2-9" 10 "7-10"
To query to which ranges a value belongs, you need to trim the ranges that the lower border is higher than the queried value, and trim the ranges that the higher border is lower.
The most efficient way I can think of is cloning one of the sets, trimming one of it sides by the rules gave above, changing the scores of the ranges to reflect the other border and then trim the second side.
Here's how to find the ranges 5 belongs to:
ZUNIONSTORE tmp 1 ranges:low
ZREMRANGEBYSCORE tmp (5 +inf
ZINTERSTORE tmp 2 tmp ranges:high WEIGHTS 0 1
ZREMRANGEBYSCORE tmp -inf (5
ZRANGE tmp 0 -1
In this discussion, Dvir Volk and #antirez suggested to use a sorted set in which each entry represent a range, and has the following form:
Member = "min-max" range
Score = max value
For example:
ZADD z 10 "0-10"
ZADD z 20 "10-20"
ZADD z 100 "50-100"
And in order to check if a value falls within a range, you can use ZRANGEBYSCORE and parse the member returned.
For example, to check value 5:
ZRANGEBYSCORE z 5 +inf LIMIT 0 1
this will return the "0-10" member, and you only need to parse the string and validate if your value is in between.
To check value 25:
ZRANGEBYSCORE z 25 +inf LIMIT 0 1
will return "50-100", but the value is not between that range.
I have a table in sql with 3 columns: BIGINT StartNumber, BIGINT EndNumber, BIGINT LocationId, and I need to be able to do something like this
Select LocationId where StartNumber < #number and EndNumber > #number.
for example:
StartNumber EndNumber LocationId
1 5 1
6 9 1
10 16 2
and when I have #number = 7 I should get LocationId = 1
How can I do this in redis?
I was thinking to move this table to redis, use sorted set and ZRANGEBYSCORE but it did't work for me:
1) When I am using ZADD key score member [score] [member], I am unable to add 2 elements with the same member and different score even with nx parameter:
zadd myset nx 1 "17" 2 "17" - it will add one element and then update its score instead of adding two elements.
2) when I am adding this: zadd set1 2 "a" 4 "b" 6 "c" 10 "d" and then trying to do zrangebyscore set1 3 3 (want to get member whose score include 3) I em getting empty result
P.s. All commands are executed on the example pages of redis website.
So as I understood the task, you don't have overlaps and each interval maps to only one location (?) and intervals don't have gaps. Based on this you can use only one sorted list with lower (or upper) bound values:
ZADD StartNumber 1 "1:5:1" 6 "6:9:1" 10 "10:16:2"
Then you can use:
ZREVRANGEBYSCORE StartNumber 7 -inf LIMIT 0 1
And it will be O(log(N)).
Put differently, your question is "how can I map N ranges of numbers to a location". One way of doing this is using two Sorted Sets, one for the StartNumber and the other one for EndNumber. Since members have to be unique, we'll also need to ensure that by using the Start/End values as part of the member. For example, with your example data, this could be done like so:
ZADD StartNumber 1 "1:5:1" 6 "6:9:1" 10 "10:16:2"
ZADD EndNumber 5 "1:5:1" 9 "6:9:1" 16 "10:16:2"
To find the location for #number=7, do ZRANGEBYSCORE StartNumber -inf 7 and ZRANGEBYSCORE EndNumber 7 +inf and intersect the results. All that remains is to split the intesect's result(s) on the colon (:) and use the 3rd element as the location.
Note: if your app ensures that there are no overlapping ranges and that there can be only one location per "number", you can get the same results with only one set.
(this is the first time that I'm giving two answers to the same question - maybe I'll get a badge or sumthin' ;))
The double Sorted Set approach is a generalization and, as such, aims to solve a bigger set of problems than what the OP needs (as put in the comments to the first answer). That approach is also not effective as the query is O(logn)+O(N) so when N is large (e.g. 5M) that's probably not a good idea.
However, to satisfy the requirements and given that the ranges do not overlap, one could actually use only a single Sorted Set and a simpler query. The set's members should be added by concatenating the EndNumber and LocationId and the their scores should be set to their respective StartNumber, so for the sake of the example:
ZADD ranges 1 "5:1" 6 "9:1" 10 "16:2"
Given #number, obtain the relevant LocationId with the following Redis Lua code (O(logn)):
-- rangelookup.lua
-- http://stackoverflow.com/questions/32185898/redis-get-member-where-score-is-between-min-and-max/32186675
-- A **non inclusive** range search on a Sorted Set with the following data:
-- score = <StartNumber>
-- member = <EndNumber>:<LocationId>
--
-- KEYS[1] - Sorted Set key name
-- ARGV[1] - the number to search
--
-- reply - the relevant id, nil if range doesn't exist
--
-- usage example: redis-cli --eval rangelookup.lua ranges , 7
local number = tonumber(ARGV[1])
local data = redis.call('ZREVRANGEBYSCORE', KEYS[1], number, '-inf', 'WITHSCORES', 'LIMIT', 0, 1)
local reply = nil
if data ~= nil and number > tonumber(data[2]) then
local to, id = data[1]:match( '(.*):(.*)' )
if tonumber(to) > number then
reply = id
end
end
return reply
Sample output:
$ redis-cli --eval rangelookup.lua ranges , 7
"1"
$ redis-cli --eval rangelookup.lua ranges , 9
(nil)
$ redis-cli --eval rangelookup.lua ranges , 99
(nil)
When i add a score for a key using zincrby, it increases the score and puts the element in lexicographical order.
Can i get this list in the order, in which the elements are updated or added ?
e.g>
If I execute
zincrby A 100 g
zincrby A 100 a
zincrby A 100 z
and then
zrange A 0 -1
then the result is
a->g->z
where, i want the result in order the entries are made so,
g->a->z
As score is same for all, redis is placing the elements in lexicographical order. Is there any way to prevent it ?
I don't think it is possible, but if you want to keep the order of insertion with scores, you should manipulate something like this:
<score><timestamp>
instead of
<score>
You will have to define a good time record (millis should be ok). Then you can use
zincrby A 100 * (10^nbdigitsformillis)
For instance:
Score = 100 and timestamps is 1381377600 seconds
That gives: 1001381377600
You incr by 200 the score: 1001381377600 + 200 * 10 = 3001381377600
Be careful with zset as it stores scores with double values (64 bits, but only 52 available for int value) so don't store more than 15-17 digits.
If you can't do that (need for great timestamp precision, and great score precision), you will have to manage two zsets (one for actual score, one for timestamp) and managing your ranking manual with the two values.