Maximum number of DB in Redis

[Peter]

Hi,
Could anyone tell me what the maximum number of database in Redis is?
I use Redis-2.2.2 and I set the number of databases in redis.conf as
follows.

databases 120

However, if I select database number greater than 16, there is an
error message.

redis> select 17
(error) ERR invalid DB index

It seems to me that Redis does not allow more than 17 databases (0 to
16)

Thanks,
Peter

[Raffaele Sena]

yap! I think 16 is the magic number (it was last time I checked :)

-- Raffaele

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[Tang Daogang]

Can anyone give answer?

--
Nothing is impossible.

[Pieter Noordhuis]

Redis supports as many databases as you want. Did you restart your
Redis instance (or pointed it at the configuration file when you
started it, for that matter) after editing the configuration?

Please keep in mind that the use of multiple databases is discouraged.
If you're using it for separating data for a single app, you can use
regular namespacing on the keys. If you're using it to separate data
from multiple apps, you could consider running a Redis server per
application instead of many applications using the same Redis server
(since Redis has a very small memory footprint when is has no data,
~1MB).

Cheers,
Pieter

[Peter]

Hi Pieter,

On Mar 8, 3:58 am, Pieter Noordhuis <pcnoordh...@gmail.com> wrote:
> Redis supports as many databases as you want. Did you restart your
> Redis instance (or pointed it at the configuration file when you
> started it, for that matter) after editing the configuration?

Yes, I did change the redis.conf file, but forgot to point the redis-
server to it. I thought that the redis.conf file is load automatically
but I was wrong. It works now

> Please keep in mind that the use of multiple databases is discouraged.
> If you're using it for separating data for a single app, you can use
> regular namespacing on the keys. If you're using it to separate data
> from multiple apps, you could consider running a Redis server per
> application instead of many applications using the same Redis server
> (since Redis has a very small memory footprint when is has no data,
> ~1MB).

Thank you for the nice trick.

Best,
Peter

[Peter]

Hi Pieter,

On Mar 8, 3:58 am, Pieter Noordhuis <pcnoordh...@gmail.com> wrote:

> Redis supports as many databases as you want. Did you restart your
> Redis instance (or pointed it at the configuration file when you
> started it, for that matter) after editing the configuration?

Thank you for pointing it out. I thought that the redis.conf will be
loaded automatically but I was wrong.
It works now

> Please keep in mind that the use of multiple databases is discouraged.
> If you're using it for separating data for a single app, you can use
> regular namespacing on the keys. If you're using it to separate data
> from multiple apps, you could consider running a Redis server per
> application instead of many applications using the same Redis server
> (since Redis has a very small memory footprint when is has no data,
> ~1MB).

[yiftach shoolman]

Hi Pieter,

Assuming you start with a minimum memory per DB (as u mentioned), is it possible to add memory on the fly while the DB is running ?

Best,

Yiftach

Peter

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[Josiah Carlson]

If you aren't using maxmemory settings, then Redis will use the memory
necessary to store the data you put in it. If you do use maxmemory
settings, I believe you can adjust it via the CONFIG SET commands. If
you mean something else, then you need to explain your question.

- Josiah

[Elben Shira]

Pieter,

Why is the use of multiple databases discouraged?

[Josiah Carlson]

I'm not Pieter, but...

1. It adds needless complexity.
2. It will go away in the future.
3. Everything that you want to do with databases can be done via other methods.

- Josiah

On Tue, Mar 8, 2011 at 4:29 PM, Elben Shira <elben...@gmail.com> wrote:
> Pieter,
> Why is the use of multiple databases discouraged?
>

[yiftach shoolman]

Hi Josiah,

So what is the best way to support multi-tenant application over Redis ? is it just by using a different key space ?

Yiftach

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Yiftach Shoolman
+972-54-7634621

[Jeremy Zawodny]

Run multiple redis-server processes, one per tenet.

Jeremy

[yiftach shoolman]

As far as I remember, the optimal configuration (performance wise) is:

  # of redis servers = # of cores / 2

Assuming I want to support thousands of tenants and to use as less as possible instances/VMs/HW.

How all this works together ?

Yiftach  

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Yiftach Shoolman
+972-54-7634621

[Jeremy Zawodny]

There's a good chance that, like many multi-tenet systems, you'll find that the bulk of the load is generated by a very few of them.  I suspect that unless you know your tenets very well (and know that they'll be very active), you shouldn't worry as much about optimal performance.

Jeremy

[Ramya Thulasingam]

Hi Peter,

I am running into the same issue. I changed the redis.conf file to have 16 databases and later restarted the redis instance but i still get the same error when i run the specs. Can you let me know how to point the redis instance to the conf file.

Thanks
Ramya

[Josiah Carlson]

I'm not Peter, but you need to run "redis-server <name of configuration file>".

 - Josiah

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