You have two options:

* [FLUSHDB][1] - clears currently active database
* [FLUSHALL][2] - clears all the existing databases


  [1]: http://redis.io/commands/flushdb
  [2]: http://redis.io/commands/flushall

Be careful here.

FlushDB deletes all keys in the current database while FlushALL deletes all keys in all databases on the current host.

*tldr: `flushdb` clears one database and `flushall` clears all databases*
## Clear CURRENT
Delete default or currently selected database (usually `0) with 

    redis-cli flushdb

## Clear SPECIFIC
Delete specific redis database with (e.g. `8` as my target database):

    redis-cli -n 8 flushdb 


## Clear ALL
Delete all redis databases with

    redis-cli flushall

With `redis-cli`:

    FLUSHDB       - Removes data from your connection&#39;s CURRENT database.
    FLUSHALL      - Removes data from ALL databases.

Redis Docs: 
[FLUSHDB](http://redis.io/commands/flushdb), 
[FLUSHALL](http://redis.io/commands/flushall)

There are right answers but I just want to add one more option (requires downtime):

1. Stop Redis.
2. Delete RDB file (find location in redis.conf).
3. Start Redis.

open your Redis cli and There two possible option that you could use:

FLUSHDB - Delete all the keys of the currently selected DB.
FLUSHALL - Delete all the keys of all the existing databases, not just the currently selected one. 

I want to force the main layout resource view to redraw / refresh, in say the Activity.onResume() method. How can I do this ? 

By main layout view, I mean the one (&#39;R.layout.mainscreen&#39; below) that is called in my Activity.onCreate(), like this:-

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.mainscreen);
    }


How to force an entire layout View refresh?

What is the main difference between Jetty and Netty? 

Netty is part of Jboss, but is it the default web server container?

Does Netty support Servlets 3.0?

What&#39;s the difference between Jetty and Netty?

I&#39;ve been playing with redis (and add some fun with it) during the last fews days and I&#39;d like to know if there is a way to empty the db (remove the sets, the existing key....) easily.  
During my tests, I created several sets with a lot of members, even created sets that I do not remember the name (how can I list those guys though ?).  
Any idea about how to get rid of all of them ?

How to empty a redis database?

<p>I've been playing with redis (and add some fun with it) during the last fews days and I'd like to know if there is a way to empty the db (remove the sets, the existing key....) easily.<br>
During my tests, I created several sets with a lot of members, even created sets that I do not remember the name (how can I list those guys though ?).<br>
Any idea about how to get rid of all of them ?</p>


I&#39;ve got a H2 database with URL `&quot;jdbc:h2:test&quot;`. I create a table using `CREATE TABLE PERSON (ID INT PRIMARY KEY, FIRSTNAME VARCHAR(64), LASTNAME VARCHAR(64));`. I then select everything from this (empty) table using `SELECT * FROM PERSON`. So far, so good.

However, if I change the URL to `&quot;jdbc:h2:mem:test&quot;`, the only difference being the database is now in memory only, this gives me an `org.h2.jdbc.JdbcSQLException: Table &quot;PERSON&quot; not found; SQL statement: SELECT * FROM PERSON [42102-154]`. I&#39;m probably missing something simple here, but any help would be appreciated.

H2 in-memory database. Table not found

If we can get data from two tables without having primary and foreign key relation, then why we need this rule? Can you please explain me clearly, with suitable example?
It&#39;s a test database, don&#39;t mind the bad structure. 

Tables&#39; structure:

**

    table - &#39;test1&#39;
    columns - id,lname,fname,dob
    no primary and foreign key and also not unique(without any constraints)

**


    **table - &#39;test2&#39;
    columns- id,native_city
    again, no relations and no constraints** 

I can still join these tables with same columns &#39;id&#39;,
so if there&#39;s no primary-foreign key, then what is the use of that?




Why is a primary-foreign key relation required when we can join without it?

Before I dive really deep into MongoDB for days, I thought I&#39;d ask a pretty basic question as to whether I should dive into it at all or not. I have basically no experience with nosql.

I did read a little about some of the benefits of document databases, and I think for this new application, they will be really great. It is always a hassle to do favourites, comments, etc. for many types of objects (lots of m-to-m relationships) and subclasses - it&#39;s kind of a pain to deal with.

I also have a structure that will be a pain to define in SQL because it&#39;s extremely nested and translates to a document a lot better than 15 different tables.

But I am confused about a few things. 

1. Is it desirable to keep your database normalized still? I really don&#39;t want to be updating multiple records. Is that still how people approach the design of the database in MongoDB?

2. What happens when a user favourites a book and this selection is still stored in a user document, but then the book is deleted? How does the relationship get detached without foreign keys? Am I manually responsible for deleting all of the links myself?

3. What happens if a user favourited a book that no longer exists and I query it (some kind of join)? Do I have to do any fault-tolerance here?

MongoDB normalization, foreign key and joining

I have changed database from [tag:PostgreSQL] to [tag:MySQL], but I don&#39;t know how to transfer data from one to other.

Does anyone know any command by which I can copy/migrate my database from [tag:PostgreSQL] to [tag:MySQL]?

Migrate database from Postgres to MySQL

I want to move table from one schema to another schema in mysql , can anybody tell me how can I do this .


move table from one schema to another schema ?

Is there any established noSQL database solution to be used for developing native mobile applications (Android and/or iOs)?

NoSQL for mobile apps?

What would be the equivalent of ERD for a NoSQL database such as MongoDB? 

Equivalent of ERD for MongoDB?

I&#39;m working on a real-time advertising platform with a heavy emphasis on performance. I&#39;ve always developed with MySQL, but I&#39;m open to trying something new like MongoDB or Cassandra if significant speed gains can be achieved. I&#39;ve been reading about both all day, but since both are being rapidly developed, a lot of the information appears somewhat dated.

The main data stored would be entries for each click, incremented rows for views, and information for each campaign (just some basic settings, etc). The speed gains need to be found in inserting clicks, updating view totals, and generating real-time statistic reports. The platform is developed with PHP.

Or maybe none of these?

MongoDB vs. Cassandra vs. MySQL for real-time advertising platform

![enter image description here][1]


  [1]: http://i.stack.imgur.com/6ejPD.png

How do I design a scheme such this in MongoDB? I think there are no foreign keys!

Foreign keys in mongo?

I currently have a live redis server running on a cloud instance and I want to migrate this redis server to a new cloud instance and use that instance as my new redis server. If it were MySQL, I would export the DB from the old server and import it into the new server. How should I do this with redis? 

P.S.: I&#39;m not looking to set-up replication. I want to completely migrate the redis server to a new instance.

How do I move a redis database from one server to another?

I&#39;ve been looking at using Redis Pub/Sub as a replacement to RabbitMQ.

From my understanding Redis&#39;s pub/sub holds a persistent connection to each of the subscribers, and if the connection is terminated, all future messages will be lost and dropped on the floor.  

One possible solution is to use a list (and blocking wait) to store all the message and pub/sub as just a notification mechanism. I think this gets me most of the way there, but I still have some concerns about the failure cases.

1. what happens when a subscriber dies, and comes back online, how should it process all it&#39;s pending messages?
2. when a malformed message comes though the system, how do you handle those exceptions? DeadLetter Queue?
3. is there a standard practice to implementing a retry policy?  

Redis Pub/Sub with Reliability

Maybe I&#39;m just blind, but I don&#39;t see an explicit [set command][1] in Redis for emptying an existing set (without emptying the entire database). For the time being, I&#39;m doing a set difference on the set with itself and storing it back into itself:

    redis&gt; SMEMBERS metasyn
    1) &quot;foo&quot;
    2) &quot;bar&quot;
    redis&gt; SDIFFSTORE metasyn metasyn metasyn
    (integer) 0
    redis&gt; SMEMBERS metasyn
    (empty list or set)

But that looks a little silly... is there a better way to do this?


  [1]: http://redis.io/commands#set

Empty/delete a set in Redis?

I like to use verbose names in Redis, for instance `set-allBooksBelongToUser:$userId`.

Is this ok or does that impact performance?

Does name length impact performance in Redis?

We have few node.js processes that should be able to pass messages, 
What&#39;s the most efficient way doing that?
How about using node_redis pub/sub

**EDIT:** the processes might run on different machines

Content Type	Original Author	Original Content on Stackoverflow
Question	Luc	View Question on Stackoverflow
Solution 1 - Database	plaes	View Answer on Stackoverflow
Solution 2 - Database	Dexter	View Answer on Stackoverflow
Solution 3 - Database	Marc	View Answer on Stackoverflow
Solution 4 - Database	Hieu Le	View Answer on Stackoverflow
Solution 5 - Database	Denys	View Answer on Stackoverflow
Solution 6 - Database	behzad babaei	View Answer on Stackoverflow

How to empty a redis database?

Database Problem Overview

Database Solutions

Solution 1 - Database

Solution 2 - Database

Solution 3 - Database

Clear CURRENT

Clear SPECIFIC

Clear ALL

Solution 4 - Database

Solution 5 - Database

Solution 6 - Database

What's the difference between Jetty and Netty?

How to force an entire layout View refresh?

Attributions