How to get the rdb location, and config file location in redis.

Sometimes when we login to a redis server, we can see the running redis on it, but we don't know where are the configuration files and the rdb backups files for the redis. In this post, we will see how to find out the location of various configuration files in redis.

The below are the important files in redis.

1. redis.conf          => main configuration file in redis
2. dump.rdb          => backup file generated by background save in redis
3. sentinel.conf     => sentinel  configuration file, required only while running sentinel
4. nodes.conf        => cluster configuration file, auto-generated by running redis in cluster mode.

Location of redis.conf

redis.conf is the major redis configuration file which has lots of very useful info and lots of highly configurable parameters.

Whether you are a developer who wants to dive more in redis or a redis admin, it is very important to read the file and try to understand the configuration params. See the sample here.

For finding out the location of redis.conf, we will use the INFO command.

info command gives a lot of very useful information about the redis server, one of which is the location of config file.

so, below command gives us the location of redis.conf file.

src/redis-cli -p 6379 info | grep 'config_file'

Location of sentinel.conf file

sentinel.conf file is only required if you are using a sentinel in redis. See the sample sentinel.conf file here. It is normally present in the same directory as redis.conf.

For finding out the sentinel.conf, we can execute the command on sentinel(note that sentinel by default runs on 26379 port while redis runs on 6379 port)

src/redis-cli -p 26379 info | grep 'config_file'

Location of dump.rdb file

dump.rdb file is the default file in which redis will save the data to disk if you enable rdb based persistence in the redis.conf file.

The location of dump.rdb can be obtained in either of the two ways

• reading the "dir" value in redis.conf file found from the location of redis.conf

           cat redis.conf | grep "dir "

• getting it from redis config

            Sometimes if we get the "dir " from the redis.conf file, it just shows the current directory( "./")

            In this case, it is better to get it from the redis config by executing the command below.

           src/redis-cli -p 6379 CONFIG GET dir

Note that #2 will only work if CONFIG command is not renamed/disabled in redis. 

If it is you will have to find out the renamed command and then use the renamed command instead of CONFIG.

Location of nodes.conf file

In a redis cluster, each cluster node/instance automatically generates a nodes.conf file where the view of the cluster with respect to that node is stored. 

It stores the cluster related information like

For all the nodes in the cluster, it stores

1. the current node, and whether it is a master or a slave.
2. no of clients connected to it.
3. slot ranges for which it holds data(if it is a master)
4. the epoch

the nodes.conf file is also stored in the same location as dump.rdb.

 

redis data types and basic commands for each in redis

Sometime when working with redis, we need to know the data type of a particular key in redis.
This is useful to know what kind of commands should be executed against that key.
A key can have any one of the below data types.

1. String
2. Hash
3. List
4. Set
5. Sorted Set
6. HLL(they are stored as string types internally)

The "TYPE" command in redis can be used to find out type of a particular key.

Lets say we have a redis instance and we find out the keys by executing the "keys *" command. For simplicity, i have separate types of keys in redis.

For each of these keys, the 'type' command will give the type of the key.

For performing basic view operations on each of the types of redis keys, below are the types and commands for each.

String

          GET  command in redis can be used to get the data in a string key.

 src/redis-cli GET mystringkey

    

Hash

         HGETALL command can be used to view the data in a hash. It returns a list of values, which consists of the key followed by the value of that key.  Like in the below, in the key "myhashkey", field1 has value value1 while field2 has value value2. Hashes are normally stored to store an object which can have many fields, like a user can have various fields like name, age, gender, etc, so that the key can be user:<userid>, fields can be name, age, gender etc and values can be 'Jurgen', 50, 'm'

src/redis-cli HGETALL myhashkey

List

        Lists in redis are infact linked list, and data can be pushed or removed from either ends.    LRANGE command in redis can be used to view the data in a list, while LLEN can be used to get the length of the list.

src/redis-cli LLEN mylistkey

src/redis-cli LRANGE mylistkey -100 100

     

Set

          Set in redis consists of unique elements. The values in set can be viewed using the SMEMBERS command. 

src/redis-cli SMEMBERS mysetkey

Zset (Sorted Set)

          Sorted Set in redis contains the string data along with a score. Finding out any entry for a particular score takes log N time where N is the number of entries stored in a key. ZRANGEBYSCORE command can be used to view the data in a sorted set. Sorted sets are normally used for storing data involving some leaderboard where each user has a particular score. Another use case where sorted sets can be useful is in reporting where the data can be stored as value and date in YYMMDD format can be stored as a score. To get the data between two dates, ZRANGEBYSCORE query can be used.

src/redis-cli ZRANGEBYSCORE mysortedsetkey -INF +INF WITHSCORES

src/redis-cli ZRANGEBYSCORE mysortedsetkey 90 100 WITHSCORES

HLL

         HyperLogLog(HLL) in redis is used to calculate the estimate the number of unique values in a key without storing the actual values!!! Sounds too good to be true, go through this link to understand more. HLLs are stored as strings, so you can do the normal GET operation on it, but to approximately calculate the number of unique keys in a key, the command which is used is PFCOUNT

src/redis-cli PFCOUNT myhllkey

So what happens when we try to try to get a key using a separate command that what is expected for that type, say when we try to GET a hash key instead of HGETALL?

We get the error, "WRONGTYPE Operation against a key holding the wrong kind of value" which is expected since we should be using HGETALL command to get the data from a hash instead of GET.

:)