I am aware of Redis having persistence option of RDB and AOF which to me is more or less entire redis cache store back-up.
Do we have persistence capability only for selected keys ?
One solution is to have long TTL but that would still be lost in case of a power failure or crash.
My requirement is not to persist entire data from redis but selected keys.
Thanks,
Ashish
No - Redis' data persistence applies to the entire dataset that the server manages, meaning all keys in all numbered databases.
If you want to persist just a bunch of keys, provision a separate Redis database for these and configure its persistency (AOF and/or RDB) accordingly.
Related
We are using redis server in production with 6 GB data size, Initially
we thought redis can be used as memory cache only, If it restarts then we can repopulate from the persistants data store with minimal downtime.
Now we realized that re-population of data from persistence store is not a good idea at all, It is causing major service downtime.
We want to evaluate redis persistant option by using RDB and AOF combination.We tried taking RDB snapshot once in a hour and committing to the AOF file with one second interval in test environments. AOF file is growing too big in test environment only. We tried to analyze the AOF file content and noticed that lot of keys we don't want to persist to the disk, We need them only in redis memory.
Is there any way to stop logging certain type of keys (block list keys) while logging to the AOF file
Generally, Redis does not provide a way to exclude certain types of keys from persistency. If you need some keys to persist to disk and others not to, you should use two independent Redis instances - one for each type and configure their persistency settings approriately. Divide and conquer.
Note: it is possible, however, to control what gets persisted in AOF inside the context if a Lua script - see the "Selective replication of commands" section of EVAL's documentation. That said, besides the consistency risks, it would be too much of a hassle to use this approach for what you need imo.
Redis SAVE and BGSAVE commands dump the complete Redis data to a persistent file.
But is there a way to dump only one DB index?
I am using the same Redis server with multiple DB indices.
I use DB 0 as config which is edited manually and contains just a small number of keys. I wish to dump this to a file as a config snapshot (versioned) to keep track of manual changes in the prod environment.
The rest of the DBs have a large number of items, that will take too long to dump, and I don't need to back them up.
Redis' persistence scope is the entire instance, meaning all shared/numbered databases and all keys in them. Saving only a subset of these is not supported.
Instead, use two independent Redis instances and configure each to persist (or not) per your needs. The overhead of running an insurance is a few megabytes so it is practically negligible.
I have multiple keys in redis most of which are insignificant and can be lost in case my redis server goes down.
However I have one or two keys, which I cannot afford to lose.
Hence I would like that whenever the server restarts, redis reads only these few keys from its persistent storage, and keep on persisting these as and when they change.
Does redis have this feature? If yes what command makes a key persisted to file and how to differ b/w persisted and unpersisted keys.
If no, What approach can I use such that I need not make my own persistent file before writing to Redis
Limitations(If the answer is no)
I do not want to change client code that enters in redis.
I cannot add more servers to redis(if any such solution exists, would like to know about it though).
EDIT
Another reason I would not want to save most keys as persistence because it is huge data, hundreds of records per second- Most of which expires in 10 minutes.
I'd like to install N redis server instances in master-slave mode.
By idea they should save to disk database-0 and do not save database-1 as security sensible data to keep it in memory only.
The same for the replication: all databses to replicate and each of slave nodes must save database-0 only but not database-1.
Is it possible to do?
It is not possible to do this. This level of fine-grained control requires multiple redis instances per persistence level and replication level.
This is perfectly fine and the recommended way to do this over redis, and in fact will give you better performance, as redis is single threaded.
What will happen to my redis data if no expiry is set and no DEL command is used.
Will it be removed after some default time ?
One more,
How redis stores data, is it in any file format ? because I can access data even after restarting the computer. So which files are created by redis and where ?
Thanks.
Redis is a in-memory data store meaning all your data is kept in RAM (ie. volatile). So theoritically your data will live as long as you don't turn the power off.
However, it also provides persistence in two modes:
RDB mode which takes snapshots of your dataset and saves them to the disk in a file called dump.drb. This is the default mode.
AOF mode which records every write operation executed by the server in an Append-Only file and then replays it thus reconstructing the original data.
Redis persistence is very good explained here and here by the creator of Redis himself.