Memcached (pronounced variously mem-cash-dee or mem-cashed) is a general-purpose distributed memory-caching system. It is often used to speed up dynamic database-driven websites by caching data and objects in RAM to reduce the number of times an external data source (such as a database or API) must be read. Memcached is free and open-source software, licensed under the Revised BSD license. Memcached runs on Unix-like operating systems (Linux and macOS) and on Microsoft Windows. It depends on the libevent library.
Memcached's APIs provide a very large hash table distributed across multiple machines. When the table is full, subsequent inserts cause older data to be purged in least recently used (LRU) order. Applications using Memcached typically layer requests and additions into RAM before falling back on a slower backing store, such as a database.
Memcached has no internal mechanism to track misses which may happen. However, some third party utilities provide this functionality.
Memcached was first developed by Brad Fitzpatrick for his website LiveJournal, on May 22, 2003. It was originally written in Perl, then later rewritten in C by Anatoly Vorobey, then employed by LiveJournal. Memcached is now used by many other systems, including YouTube, Reddit, Facebook, Pinterest, Twitter, Wikipedia, and Method Studios. Google App Engine, Google Cloud Platform, Microsoft Azure, IBM Bluemix and Amazon Web Services also offer a Memcached service through an API.
The system uses a client–server architecture. The servers maintain a key–value associative array; the clients populate this array and query it by key. Keys are up to 250 bytes long and values can be at most 1 megabyte in size.
Clients use client-side libraries to contact the servers which, by default, expose their service at port 11211. Both TCP and UDP are supported. Each client knows all servers; the servers do not communicate with each other. If a client wishes to set or read the value corresponding to a certain key, the client's library first computes a hash of the key to determine which server to use.
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Multiprocessors are a core component in all types of computing infrastructure, from phones to datacenters. This course will build on the prerequisites of processor design and concurrency to introduce
The course introduces the students to the basic notions
of computer architecture and, in particular, to the
choices of the Instruction Set Architecture and to the
memory hierarchy of modern systems.
En informatique et en bases de données, NoSQL désigne une famille de systèmes de gestion de base de données (SGBD) qui s'écarte du paradigme classique des bases relationnelles. L'explicitation la plus populaire de l'acronyme est Not only SQL (« pas seulement SQL » en anglais) même si cette interprétation peut être discutée. La définition exacte de la famille des SGBD NoSQL reste sujette à débat. Le terme se rattache autant à des caractéristiques techniques qu'à une génération historique de SGBD qui a émergé autour des années 2010.
In computing, a distributed cache is an extension of the traditional concept of cache used in a single locale. A distributed cache may span multiple servers so that it can grow in size and in transactional capacity. It is mainly used to store application data residing in database and web session data. The idea of distributed caching has become feasible now because main memory has become very cheap and network cards have become very fast, with 1 Gbit now standard everywhere and 10 Gbit gaining traction.
A database shard, or simply a shard, is a horizontal partition of data in a database or search engine. Each shard is held on a separate database server instance, to spread load. Some data within a database remains present in all shards, but some appear only in a single shard. Each shard (or server) acts as the single source for this subset of data. Horizontal partitioning is a database design principle whereby rows of a database table are held separately, rather than being split into columns (which is what normalization and vertical partitioning do, to differing extents).
Explore la conception de mémoire cache, les succès, les ratés et les politiques d'expulsion dans les systèmes informatiques, en mettant l'accent sur la localité spatiale et temporelle.
Explore l'évaluation des performances de la mémoire cache, couvrant les points de repère, la loi d'Amdahl, les performances du processeur, la hiérarchie de la mémoire, les optimisations de cache et les caches multiniveaux.
Explore les optimisations logicielles pour l'efficacité du cache, l'exécution parallèle et l'équilibrage de charge.
Database workloads have significantly evolved in the past twenty years. Traditional database systems that are mainly used to serve Online Transactional Processing (OLTP) workloads evolved into specialized database systems that are optimized for particular ...
Modern large-scale data platforms manage colossal amount of data, generated by the ever-increasing number of concurrent users. Geo-replicated and sharded key-value data stores play a central role when building such platforms. As the strongest consistency m ...
EPFL2020
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Caching is a technique that alleviates networks during peak hours by transmitting partial information before a request for any is made. In a lossy setting of Gaussian databases, we study a single-user model in which good caching strategies minimize the dat ...