I took over a project that is using Redis for temporary storage of objects in a queue. I want to know how I can dump all the objects on a nightly basis. The business only operates from 8am to 8pm and the jobs are completed daily so every day we start fresh.
So my I was wondering how to dump or delete all the data from Redis at midnight.
FYI - dumping data in the Redis terminology actually means saving it to disk. It appears that what you want is to remove all the data.
There are many ways to do what you want, but basically you need to set up a cron job or similar that executes a FLUSHALL for example. Alternatively, if your Redis server isn't configured with disk persistence, you can simply restart it.
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We have redis cluster which holds more than 2 million and these keys has been updated with the time interval of 1 minute. Now we have a requirement to take the snapshot of the redis db in a particular interval For eg every 10 minute. This snapshot should not pause the redis command execution.
Is there any async way of taking snapshot from redis ?
It would be really helpful if we get any suggestion on open source tools or frameworks.
The Redis BGSAVE is async and takes a snapshot.
It calls the fork() function of the OS. According to the Redis manual,
Fork() can be time consuming if the dataset is big, and may result in Redis to stop serving clients for some millisecond or even for one second if the dataset is very big and the CPU performance not great
Two million updates in one minutes, that is 30K+ QPS.
So you really have to try it out, run the benchmark that similutes your business, then issue BGSAVE, monitor the I/O and CPU usage of your system, and see if there's a spike in your redis calling latency.
Then issue LASTSAVE, which will tell you when your last success snapshot happened. So you can adjust your backup schedule.
Imagine setup of Redis Cluster for example, or just usual sharded setup, where we have N > 1 Redis processes per physical node. All our processes have same redis.conf and enabled SAVE options there with same SAVE period. So, if all our main Redis processes started on the same time - all of them will start SAVE on the same time or around it.
When we have 9 Redis processes and all of them start RDB snapshotting on the same time it:
Affects performance, because we make 9 forked processes that start consume CPU and do IO on the same time.
Requires too much reserved additional memory that can't be used as actual storage, because on write-heavy application Redis may use up to 2x the memory normally used during snapshotting. So... if we want to have redis processes for 100Gb on this node - we should take additional 100Gb for forking all processes on the same time to be safe.
Is there any best practice to modify this setup and make Redis processes start saving one by one or at least with some randomization?
I have only one idea with disabling schedule in redis.conf and write cron script that will start save one by one with time lag. But this solution looks like a hack and it should be some other practices here.
I read article about backing up data, but some issues is not clear for me:
What happens with data, that will be changed after backup process
was started?
Does backup operation work only on current machine? Or will it collect
data from all shards in cluster? If only on current, should I start
backup process on all servers?
Is it slow operation so I should forbid all operation to db while
backup in progress?
If a row changes while the backup is going on, the new value may or may not be in the backup. This is generally OK because RethinkDB only offers single-row atomicity anyway, but if you have a workload where that isn't OK then your other options are to use a filesystem that lets you snapshot the data on disk, or to add a new server to your cluster and set it as a replica of the table you want to back up.
It collects data from all shards.
It can take a very long time.
We have big shopping and product dealing system. We have faced lots problem with MySQL so after few r&D we planned to use Redis and we start integrating Redis in our system.
Following this previously directly hitting the database now we have moved the Redis system
User shopping cart details
Affiliates clicks tracking records
We have product dealing user data.
other site stats.
I am not only storing the data in Redis system i have written crons which moves Redis data in MySQL data at time intervals. This is the main point i am facing the issues.
Bellow points i am looking for solution
Is their any other ways to dump big data from Redis to MySQL?
Redis fail our store data in file so is it possible to store that data directly to MySQL database?
Is Redis have any trigger system using that i can avoid the crons like queue system?
Is their any other way to dump big data from Redis to MySQL?
Redis has the possibility (using bgsave) to generate a dump of the data in a non blocking and consistent way.
https://github.com/sripathikrishnan/redis-rdb-tools
You could use Sripathi Krishnan's well-known package to parse a redis dump file (RDB) in Python, and populate the MySQL instance offline. Or you can convert the Redis dump to JSON format, and write scripts in any language you want to populate MySQL.
This solution is only interesting if you want to copy the complete data of the Redis instance into MySQL.
Does Redis have any trigger system that i can use to avoid the crons like queue system?
Redis has no trigger concept, but nothing prevents you to post events in Redis queues each time something must be copied to MySQL. For instance, instead of:
# Add an item to a user shopping cart
RPUSH user:<id>:cart <item>
you could execute:
# Add an item to a user shopping cart
MULTI
RPUSH user:<id>:cart <item>
RPUSH cart_to_mysql <id>:<item>
EXEC
The MULTI/EXEC block makes it atomic and consistent. Then you just have to write a little daemon waiting on items of the cart_to_mysql queue (using BLPOP commands). For each dequeued item, the daemon has to fetch the relevant data from Redis, and populate the MySQL instance.
Redis fail our store data in file so is it possible to store that data directly to MySQL database?
I'm not sure I understand the question here. But if you use the above solution, the latency between Redis updates and MySQL updates will be quite limited. So if Redis fails, you will only loose the very last operations (contrary to a solution based on cron jobs). It is of course not possible to have 100% consistency in the propagation of data though.
Is Redis memory only store like memcached or does it write the data to the disk? If it does write to the disk, how often is the disk written to?
Redis persistence is described in detail here:
http://redis.io/topics/persistence
By default, redis performs snapshotting:
By default Redis saves snapshots of the dataset on disk, in a binary file called dump.rdb. You can configure Redis to have it save the dataset every N seconds if there are at least M changes in the dataset, or you can manually call the SAVE or BGSAVE commands.
For example, this configuration will make Redis automatically dump the dataset to disk every 60 seconds if at least 1000 keys changed: save 60 1000
Another good reference is this link to the author's blog where he tries to explain how redis persistance works:
http://antirez.com/post/redis-persistence-demystified.html
Redis holds all data in memory. If the size of an application's data is too large for that, then Redis is not an appropriate solution.
However, Redis also offers two ways to make the data persistent:
1) Snapshots at predefined intervals, which may also depend on the number of changes. Any changes between these intervals will be lost at a power failure or crash.
2) Writing a kind of change log at every data change. You can fine-tune how often this is physically written to the disk, but if you chose to always write immediately (which will cost you some performance), then there will be no data loss caused by the in-memory nature of Redis.