X-Git-Url: https://git.saurik.com/redis.git/blobdiff_plain/45636487143097d360dfba4f3fa602b08927e355..570333015147ce01646ff61e50afc210a12408db:/doc/README.html diff --git a/doc/README.html b/doc/README.html index 4ad8c0ed..38242aa0 100644 --- a/doc/README.html +++ b/doc/README.html @@ -26,10 +26,11 @@
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Introduction

Redis is a database. To be more specific redis is a very simple database -implementing a dictionary where keys are associated with values. For example -I can set the key "surname_1992" to the string "Smith". The interesting thing about Redis is that values associated to keys are not limited to simple strings, they can also be lists and sets, with a number of server-side atomic operations associated to this data types.

Redis takes the whole dataset in memory, but the dataset is persistent -since from time to time Redis writes a dump of the dataset on disk asynchronously. The dump is loaded every time the server is restarted.

Redis can be configured to save the dataset after a given number of seconds elapzed and changes to the data set. For example you can tell Redis to save after 1000 changes and at least 60 seconds sinde the same save. You can specify a number of this combinatins.

Because data is written asynchronously, If a system crash occurs the last few queries can get lost (that is acceptable in many applications). Redis supports master-slave replication from the early days in order to make this a non issue if your application is of the kind where even few lost records are not acceptable.

Beyond key-value databases

In most key-value databases keys and values are simple strings. In Redis keys are just strings too, but the associated values can be Strings, Lists and Sets, and there are commands to perform complex atomic operations against this data types, so you can think at Redis as a data structures server.

For example you can append elements to a list stored at the key "mylist" using the LPUSH or RPUSH operation in O(1). Later you'll be able to get a range of elements with LRANGE or trim the list with LTRIM. Sets are very flexible too, it is possible to add and remove elements from Sets (unsorted collections of strings), and then ask for server-side intersection, union, difference of Sets.

All this features, the support for sorting Lists and Sets, allow to use Redis as the sole DB for your scalable application without the need of any relational database. We wrote a simple Twitter clone in PHP + Redis to show a real world example, the link points to an article explaining the design and internals in very simple words.

What are the differences between Redis and Memcached?

In the following ways:

+

Introduction

Redis is a database. To be specific, Redis is a very simple database implementing a dictionary, where every key is associated with a value. For example I can set the key "surname_1992" to the string "Smith". +What makes Redis different from many other key-value stores, is that every single value has a type. The following types are supported:

+The type of a value determines what operations (called commands) are available for the value itself. +For example you can append elements to a list stored at the key "mylist" using the LPUSH or RPUSH command in O(1). Later you'll be able to get a range of elements with LRANGE or trim the list with LTRIM. Sets are very flexible too, it is possible to add and remove elements from Sets (unsorted collections of strings), and then ask for server-side intersection, union, difference of Sets. Each command is performed through server-side atomic operations. +Please refer to the Command Reference to see the full list of operations associated to these data types.

In other words, you can look at Redis as a data structures server. A Redis user is virtually provided with an interface to Abstract Data Types, saving her from the responsibility to implement concrete data structures and algorithms. Indeed both algorithms and data structures in Redis are properly choosed in order to obtain the best performance.

Redis loads and mantains the whole dataset into memory, but the dataset is persistent, since from time to time Redis writes a dump on disk asynchronously. The dataset is loaded from the dump every time the server is (re)started.

Redis can be configured to save the dataset when a certain number of changes is reached and after a given number of seconds elapses. For example, you can configure Redis to save after 1000 changes and at most 60 seconds since the last save. You can specify any combination for these numbers.

Because data is written asynchronously, when a system crash occurs, the last few queries can get lost (that is acceptable in many applications). Anyway it is possible to make this a non issue, since Redis supports master-slave replication from its early days, being effective even in the case where a few records lost are not acceptable.

Beyond key-value databases

All these features allow to use Redis as the sole DB for your scalable application without the need of any relational database. We wrote a simple Twitter clone in PHP + Redis to show a real world example, the link points to an article explaining the design and internals in very simple words.

What are the differences between Redis and Memcached?

In the following ways:

What are the differences between Redis and Tokyo Cabinet / Tyrant?

Redis and Tokyo Cabinet can be used for the same applications, but actually they are very different beasts. If you read twitter messages of people involved in scalable things both products are reported to work well, but surely there are times where one or the other can be the best choice. Some differences are the followings (I may be biased, make sure to check yourself both the products).

@@ -100,7 +101,6 @@ learn all the commands supported by Redis and the LicenseRedis is released under the BSD license. See the COPYING file for more information.

Credits

Redis is written and maintained by Salvatore Sanfilippo, Aka 'antirez'.

Enjoy, antirez -