Imagine these two scenarios for REDIS-SERVER:
(A)redis-cli> set "firstname lastname.AT.emailaddress.dot.com" "1"
(B)redis-cli> setbit "firstname lastname.AT.emailaddress.dot.com" 1 1
If 1 million different keys are stored with customer name/email.
Use case is that i would like to check if record exists,
so
in case of (A)
redis-cli> get "firstname lastname.AT.emailaddress.dot.com"
reply from REDIS would be> 1
in case of (B)
redis-cli> getbit "firstname lastname.AT.emailaddress.dot.com" 1
reply from REDIS would be> 1
Question:
Will there be any difference in the amount of memory used by REDIS if all one million key/value pairs are kept in memory for query?
You should use solution A. It's more meaningful, and costs less memory, since Redis has special encoding for small integers. In your case, the value part, i.e. "1", won't cost extra memory.
Also, another solution is to use a SET to save these name/email pairs: use SADD name-email "firstname lastname.AT.emailaddress.dot.com" to add record, and use SISMEMBER name-email "firstname lastname.AT.emailaddress.dot.com" to check the existence.
Related
I have many different keys. some start with "user USERNAME" and many others.
is there a way to get a random key from the "user *" ?
if so, how can i get like 5 different users?
If you put all the usernames into a Redis set, then you could use the SRANDMEMBER command to randomly gets usernames from the set. Example from the documentation:
redis> SADD myset one two three
(integer) 3
redis> SRANDMEMBER myset
"three"
redis> SRANDMEMBER myset 2
1) "three"
2) "two"
The set seems to be the only Redis data type that can return random elements from the collection. You might have to process your data a little differently to do this.
You can definitely use a Set and store all your "user*" key names in it, as suggested by #Sunil D.
Alternatively, you could use a dedicated Redis database for your "user*" keys and then use the RANDOMKEY command to fetch keys from it. The nice thing about this is that you don't have to manage the Set of key names (i.e. add and remove to it whenever a key is created or deleted, respectively).
Note, however, that with both approaches, you'll have to check that the result you got wasn't returned earlier after each call to SRANDMEMBER or RANDOMKEY since both do not ensure that you'll get a different answer each time you invoke it.
On my current project I'm implementing autocompletion service on top of Redis, for it I use such approach (this article describes it more widely):
1) for storing dump of the data I have hash in which I put searchable objects as a values, for instance
HSET data 1 "{\"name\":\"Kill Bill\",\"year\":2003}"
HSET data 2 "{\"name\":\"King Kong\",\"year\":2005}"
2) for storing all possible sequences of input characters (that I generate in advance) which could be used in search I use sorted sets, like
ZADD search:index:k 0 1
ZADD search:index:ki 0 1
ZADD search:index:kil 0 1
ZADD search:index:kill 0 1
Where value stored in sorted set (in my example '1') is key for data from hash. So, for searching some data (for example where name started with 'ki') we need to make two steps:
data_keys = REDIS.zrevrange('search:index:ki', 0, -1)
matching_data = REDIS.hmget(data, *data_keys)
The issue I tried to solve - how automatically remove all data from sorted sets related to hash values when I removed it? In relational databases I can use cascade deletion for such cases, but how can I handle it in Redis?
Your design appears awkward to me, I'm unsure what you're actually trying to do with Redis and perhaps that could be the topic of another question.
That said, to address your question, Redis does offer a "cascading delete"-like behavior. Instead, if you're deleting hash "1", iterate the prefix and ZREM it from the relevant sorted sets.
Note: do not use a Lua script for this task, as it will generate key names (i.e. sorted sets by prefix) and that is against the recommendations (will not work on a cluster)
I am trying to write a query in Redis to get the first 2 field values of my hash key..
Basically, when I do HVALS hashname, I want to get the values of the first 2 fields added (the oldest 2). This is somewhat like getting the TOP 2 tuples in a SQL database.
Is this possible in redis?
No, this isn't possible. The order of fields and values in a Redis Hash is for all intents and purposes random (despite the empirical evidence obtained on from experimenting on smallish Hashes). For ordering elements, refer to Redis' Sorted Sets.
Update: to answer the question in the comment, IIUC it looks like you can solve it easily with just Strings. Because of Redis' nature, at any given moment there is either one user waiting for a specific match, or zero. You can SET matchmaking:blue username1:token if the key doesn't exist (i.e. zero users waiting for the match) and GET and DEL it if it exists. Be sure to use SET's "NX" subcommand, MULTI/EXEC and/or Lua to ensure the atomicity of these two logical operations.
From what I have experimented with, HVALS returns values for keys in the order you're looking for i.e. oldest key first. Now its up to you to only pick the first two values using the client program e.g. HSET myhmap name "abhi" , HSET myhmap email "test#test" , HSET myhmap planet "earth", HSET myhmap galaxy "andromeda". HVALS myhmap will return "abhi","test#test", "earth" , "andromeda"
I am trying to insert time based records with multiple fields on the values (with TTL enabled).
For the multiple fields the best way to do it via Redis is using HSET:
HSET user:32 name "johns" timecreated "3333311232" address "somewhere"
I also try to read those values via time range:
for example return all history records (for example user 32) which was inserted in the last day:
so the best for that would be storing via ZADD using scores(this time I am losing the hash-map structure for easy retrieval):
ZADD user:32 3333311232 "name=johns,timecreated=3333311232,address=somewhere"
On the top of the things I want to add TTL for each record
Any idea how I could optimize my design?
I could split into two but that will requires two queries when reading:
ZADD user:32 3333311232 "user:32:3333311232"
HMSET user:32:3333311232 name “johns” timecreated “3333311232” address="somewhere"
than to retrieve ill need:
//some range
ZRANGEBYSCORE user:32 3333311232 333331123
result: 1389772850
now to get all information: HGETALL user:32:1389772850
What do you think?
Thank you,
ray.
The two methods you describe are the two common approaches. If you store the entire object in the ZSET, you would typically store it as a JSON string. If you don't need "random" access to the object, that's a valid approach.
I usually go for the other approach; a ZSET combined with hashes. the two queries are not a big deal. You could even abstract it away with a Lua script; see EVAL.
Regarding the TTL, while you cannot expire individual ZSET values, you could expire the hash, and use keyspace notifications to listen for the expired event, and remove the corresponding value from the ZSET.
Let me know if you need some more specifics.
In redis I store objects in a sorted set.
In my solution, it's important to be able to run a ranged query by dates, so I store the items with the score being the timestamp of each items, for example:
# Score Value
0 1443476076 {"Id":"92","Ref":"7ADT","DTime":1443476076,"ATime":1443901554,"ExTime":0,"SPName":"7ADT33CFSAU6","StPName":"7ADT33CFSAU6"}
1 1443482969 {"Id":"11","Ref":"DAJT","DTime":1443482969,"ATime":1443901326,"ExTime":0,"SPName":"DAJTJTT4T02O","StPName":"DAJTJTT4T02O"}
However, in other situations I need to find a single item in the set based on it's ID.
I know I can't just query this data structure as if it were a nosql db, but I tried using ZSCAN, which didn't work.
ZSCAN MySet 0 MATCH Id:92 count 1
It returns; "empty list or set"
Maybe I need to serialize different?
I have serialized using Json.Net.
How, if possible, can I achieve this; using dates as score and still be able to lookup an item by it's ID?
Many thanks,
Lars
Edit:
Assume it's not possible, but any thoughts or inputs are welcome:
Ref: http://openmymind.net/2011/11/8/Redis-Zero-To-Master-In-30-Minutes-Part-1/
In Redis, data can only be queried by its key. Even if we use a hash,
we can't say get me the keys wherever the field race is equal to
sayan.
Edit 2:
I tried to do:
ZSCAN MySet 0 MATCH *87*
127.0.0.1:6379> ZSCAN MySet 0 MATCH *87*
1) "192"
2) 1) "{\"Id\":\"64\",\"Ref\":\"XQH4\",\"DTime\":1443837798,\"ATime\":1444187707,\"ExTime\":0,\"SPName\":\"XQH4BPGW47FM\",\"StPName\":\"XQH4BPGW47FM\"}"
2) "1443837798"
3) "{\"Id\":\"87\",\"Ref\":\"5CY6\",\"DTime\":1443519199,\"ATime\":1444172326,\"ExTime\":0,\"SPName\":\"5CY6DHP23RXB\",\"StPName\":\"5CY6DHP23RXB\"}"
4) "1443519199"
And it finds the desired item, but it also finds another one with an occurance of 87 in the property ATime. Having more unique, longer IDs might work this way and I would have to filter the results in code to find the one with the exact value in its property.
Still open for suggestions.
I think it's very simple.
Solution 1(Inferior, not recommended)
Your way of ZSCAN MySet 0 MATCH Id:92 count 1 didn't work out because the stored string is "{\"Id\":\"92\"... not "{\"Id:92\".... The string has been changed into another format. So try to use MATCH Id\":\"64 or something like that to match the json serialized data in redis. I'm not familiar with json.net, so the actual string leaves for you to discover.
By the way, I have to ask you did ZSCAN MySet 0 MATCH Id:92 count 1 return a cursor? I suspect you used ZSCAN in a wrong way.
Solution 2(Better, strongly recommended)
ZSCAN is good when your sorted set is not large and you know how to save network roundtrip time by Redis' Lua transaction. This still make "look up by ID" operation O(n). Therefore, a better solution is to change you data model in the following way:
change sorted set
from
# Score Value
0 1443476076 {"Id":"92","Ref":"7ADT","DTime":1443476076,"ATime":1443901554,"ExTime":0,"SPName":"7ADT33CFSAU6","StPName":"7ADT33CFSAU6"}
1 1443482969 {"Id":"11","Ref":"DAJT","DTime":1443482969,"ATime":1443901326,"ExTime":0,"SPName":"DAJTJTT4T02O","StPName":"DAJTJTT4T02O"}
to
# Score Value
0 1443476076 Id:92
1 1443482969 Id:11
Move the rest detailed data in another set of hashes type keys:
# Key field-value field-value ...
0 Id:92 Ref-7ADT DTime-1443476076 ...
1 Id:11 Ref-7ADT DTime-1443476076 ...
Then, you locate by id by doing hgetall id:92. As to ranged query by date, you need do ZRANGEBYSCORE sortedset mindate maxdate then hgetall every id one by one. You'd better use lua to wrap these commands in one and it will still be super fast!
Data in NoSql database need to be organized in a redundant way like above. This may make some usual operation involve more than one commands and roundtrip, but it can be tackled by redis's lua feature. I strongly recommend the lua feature of redis, cause it wrap commands into one network roundtrip, which are all executed on the redis-server side and is atomic and super fast!
Reply if there's anything you don't know