my redis version:3.0.2
Hash data as below show.
key name:test
contents(values):
1) "xx1"
2) "1"
3) "xx2"
4) "2"
5) "xx3"
6) "3"
7) "xx4"
8) "4"
9) "xx5"
10)"5"
use commond -->HSCAN test 0 COUNT 2
Redis return every key and value, not the first of 2 keys and values!
COUNT option for SCAN does not limit the number of key-values returned.
It is used to force the command to increase the number key-values returned.
Redis COUNT option doc:
When iterating Sets encoded as intsets (small sets composed of just
integers), or Hashes and Sorted Sets encoded as ziplists (small hashes
and sets composed of small individual values), usually all the
elements are returned in the first SCAN call regardless of the COUNT
value.
So, get first two values from the result of HSCAN test 0 command.
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 use sorted set in Redis.
The common value of data in sorted set is over one million. How can I read this sorted set by partitions? I mean first 100 000 rows and the following?
There is only one command to take data: smembers set
You can use the ZRANGE command on your sorted set and specify the start and stop to get 100,000 entries, and then 100,001 to 200,000 for the next ZRANGE.
ZRANGE documentation on Redis.io
You mentioned using smembers set to take data, but that is used only on non-sorted sets. If you are actually using a non-sorted set, then you would need to use SPOP and define your count at 100,000. However, this would simultaneously remove all those entries.
SPOP documentation on Redis.io
You can iterate through the elements of an unsorted set incrementally using SSCAN. Start with cursor 0 and use the returned cursor in subsequent calls, until 0 is returned again.
pantalones:6379> SSCAN five-characters 0 COUNT 3
1) "7"
2) 1) "d"
2) "e"
3) "a"
4) "c"
pantalones:6379> SSCAN five-characters 7 COUNT 3
1) "0"
2) 1) "b"
In this example, the first call to SSCAN returns a cursor of 7, which is then provided to the second call to SSCAN. The second call returns a cursor of 0, so we know the iteration is complete.
See SSCAN documentation on Redis.io.
I got several sorted sets with a common prefix (itemmovements:) in Redis.
I know we can use ZCOUNT to get the number of items for a single (sorted set) key like this:
127.0.0.1:6379> zcount itemmovements:8 0 1000000000
(integer) 23
(I am able to do this, since I know the range of the item scores.)
How to run this in a loop for all keys prefixed itemmovements:?
Taking hint from How to atomically delete keys matching a pattern using Redis I tried this:
127.0.0.1:6379> EVAL "return redis.call('zcount', unpack(redis.call('keys', ARGV[1])), 0, 1000000000)" 0 itemmovements:*
(integer) 150
but as you can see it just returns a single number (which happens to be the size of itemmovements:0, the first value returned by keys).
I realized I did not understand what that lua code in EVAL was doing. The code below works fine:
eval "local a = {}; for _,k in ipairs(redis.call('keys', 'itemmovements:*')) do table.insert(a, k); table.insert(a, redis.call('zcount', k, 0, 1000000000)); end; return a" 0
For lists I can do the operation:
LLEN KeyName
and it will return the size of a list in Redis. What is the equivalent command for sets? I can't seem to find this in any documentation.
You are looking for the SCARD command:
SCARD key
Returns the set cardinality (number of elements) of the set stored at
Return value
Integer reply: the cardinality (number of elements) of the set, or 0 if key does not exist.
You can view all of the set commands on the documentation webpage.
If it's a sorted set, you can use
ZCOUNT myset -inf +inf
or
ZCARD myset
zCard is short for cardinality (cardinality is the number of elements in a set). It gives you total number of members inside of a "sorted set".
Sometimes you might wanna extract how many members are inside of a range in a sorted set. For that you can use zCount.
ZCOUNT cars 0 50 // inclusive
this will include 0 and 55. 0 <= .... <=50. But if you do not want to include them
ZCOUNT cars (0 (50
if it is regular set
SCARD cars
I have a Sorted set and want to get all members of set. How to identify a max/min score for command :
zrange key min max
?
You're in luck, as zrange does not take scores, but indices. 0 is the first index, and -1 will be interpreted as the last index:
zrange key 0 -1
To get a range by score, you would call zrangebyscore instead -- where -inf and +inf can be used to denote negative and positive infinity, respectively, as Didier Spezia notes in his comment:
zrangebyscore key -inf +inf
Starting with Redis 6.2.0,
To get all the keys and its value together in a single query using the below,
zrange <KEY> 0 -1 WITHSCORES
The optional WITHSCORES argument supplements the command's reply with the scores of elements returned. The returned list contains value1,score1,...,valueN,scoreN instead of value1,...,valueN. Client libraries can return a more appropriate data type (suggestion: an array with (value, score) arrays/tuples).
In newer versions of redis (>= v6.2.0), if you want to get all members of a sorted set between two scores, you should use:
ZRANGE key min max BYSCORE
Adding the BYSCORE option makes redis treat the min & max arguments as scores rather than indices.
(As of this writing, ZRANGEBYSCORE still works, but is considered deprecated.)