First: this here is the unofficial FAQ, only containing things that come up by users in the IRC channel #redis on Freenode. There's also a more official FAQ. This document is also available on my site.
Maybe. To better help please give the following info:
- Output of
redis-cli INFO - Output of
redis-cli CONFIG GET '*'
Don't spam the channel, upload it to pastebin, as a gist or similar.
I want to use SELECT to seperate my data. Is this a good idea?
Antirez decided select was an anti-pattern a loooong time ago. He won't fully deprecate it, but it doesn't get support in new features such as cluster. (via brycebaril)
Just use seperate instances or use namespacing (often used: namespace:real-key-name)
Sorted Sets can be useful here. Store some value and use the timestamp as the score. Then use ZRANGEBYSCORE to get it back.
- Make sure the old instance is already stopped.
pidof redis-serverorps aux | grep [r]edis-servershould only list one PID. - Make sure you're starting redis from the right path (if installed manually it might be different than when installed from your package manager)
- Make sure you're connecting to the right port. It is possible to run multiple instances on different ports (default port is 6379)
If you're used to SQL, storing data in Redis is more like creating the indexes for your SQL schema (from: brycebaril)
First: check that master and slave are in sync. Do this by checking INFO replication of both master and slave and compare master_repl_offset and slave_repl_offset.
Next: Do you have a lot of expires? On initial sync the slave will drop all already expired keys, while they may still be in the master instance (but are gone as soon as you try to fetch them). (by: Moe, also sync not copying all keys)
You have multiple possibilities to do this.
- Take what the Ubuntu repository provides:
apt-get install redis-server(this may be a little bit old) - Compile it yourself, see Download, Section "Installation"
- Use a PPA (Personal Package Archive), such as the one by chris-lea or rwky
Redis does not have a default path to put the config in. Instead you always have to specify it as a argument on the command line (or in your init script). Most distributions put the config into /etc/redis.conf, /etc/redis/redis.conf, /var/lib/redis/redis.conf or something similar. So look there first if you uncertain.
I can't compile Redis. It fails with something like "error: no such file or directory: '../deps/hiredis/libhiredis.a'"
Try a make distclean first, then again a make. The compile step tries to be smart by only building dependencies once and use the old compile configuration. But it one of the dependencies fails it does not try to compile them again and thus fails. make distclean removes all previous saved state.
Yes, Redis' pubsub mechanism is quite good. People get excited about it. But it might not be the best option for your use case. Pub/Sub is fire-and-forget. If you publish to a channel and no one is subscribed, that message is lost. It's not persisted, saved for later or held back. Just lost. This might or might not be what you want. For more read section 1.1 of matt's Pub/Sub intro
Ok, I understand Pub/Sub, I really want to use it. Does it work with hundred or thousands of subscriptions/clients?
The mechanism to subscribe to a channel is quite cheap, consider it an constant-time operation. Publish is more expensive, it needs to send to all subscribed clients. For a much more details info read the mailing list thread
If there is no suitable Replica to failover to, the whole Redis Cluster will go into a fail state and won't serve any more queries.
It will become available when all slots are covered again (either by resharding or bringing the old Master back).
You can change this behaviour and always serve queries by setting cluster-require-full-coverage to no.
See the default config for more.
