Memcached - Web DevelopmentYouTube↗  IA↗(long shot)
Education  13.5K views 115 likes 3 dislikes   23 Feb 2015
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Memcached is a very fast in-memory cache. It was built
memcachedは高速なインメモリ･キャッシュです
by a company called Danja, to power a website called
Dangaが自社のWebサイト LiveJournalの強化のために設計しました
LiveJournal. And before Facebook took over the world, LiveJournal was
Facebookが世界を席巻するまでLiveJournalは
a very popular site where people had you know, their
人気のブログ開設サイトでした
own blogs. Kind of like Tumblr or Blogspot. I don't
TumblrやBlogspotのようなものです
know a bunch of, a bunch of things have, have
かなりの数のWebサイトが台頭し
risen to take the, the place of LiveJournal. But LiveJournal
LiveJournalに取って代わりました
was a very popular site back in the day. And when
しかしLiveJournalは当時とても人気がありました
I say back in the day, I mean 2003 is when memcache was released. Now just
当時というのは2003年頃で ちょうどmemcachedが公開された年です
about every website on the internet uses memcache
今やネット上のほとんどのWebサイトで 使われるほどmemcachedは普及しました
these days. I don't know about Google but
Googleについては分かりませんが
certainly it's used by Facebook. It's used by
Facebookで採用されています
Reddit. You know, it's used by YouTube. Twitter,
RedditやYouTube、Twitterでも使われています
it is an essential piece of software when
Webアプリケーションを書く際に
you're writing web applications. And in fact other than,
不可欠なソフトウエアの1つです　Linuxを除けば
than Linux itself memcache is probably the piece of software
memcachedはおそらく インターネット上のWebサイトにおいて
that's, most in common between every website online. It's, it's pretty
最も普及しているソフトウエアでしょう
astounding. It's very, very simple. And it's very, very effective
memcachedは驚くほどシンプルで効果的なのです
at what it does. Okay. To draw a bigger version of
では先ほどの小テストの図を大きく描きます
that picture I did on the quiz, how memcached fits
memcachedを組み込む方法は
in, it looks something like this. Memcached is a process. Often
次のようになります　memcachedはプロセスです
you run it on its own machine. But you can also
通常マシン上で起動させますが
run it on the machines with your APP servers, and it's
複数のAPサーバと一緒に起動することもできて
a very simple system. The algorithm doesn't change. A request
シンプルなシステムです　アルゴリズムは変わりません
comes in we check memcached. If a response is there, we
リクエストがくるとmemcachedを調べ レスポンスがあれば
send it back to the user. If it isn't there
ユーザに戻します　レスポンスがなければ
we check the database instead. And right to memcached, you know.
データベースをチェックし memcachedに書き込みます
As we've been doing, the algorithm should be pretty familiar
今までの講義でアルゴリズムは理解できているはずです
to you by now. What's handy about it, is that all
すべてのAPサーバがmemcachedを
of these apps servers can interact with memcached. Memcached is
使えるのはとても便利です
fast enough and can support many, many sockets that it works
非常に速く 多数のソケットをサポートしており
very well in this scenario. Also most memcached libraries have built
このシナリオでうまく動作します 更にほとんどのmemcachedライブラリは
in towards this notion of having multiple memcached machines. Because memcached
memcachedマシンを複数使うという想定で 作られています
is just a key value store. Just, it's like basically a
Key-Valueストア方式をとっているからです
giant hash table. You can hash on the keys to decide which
基本的には巨大なハッシュテーブルのようなものです
server to send your data to. And because it's a cache
ハッシュ値を計算しデータを送るサーバを決められます
it's okay if you, you know, lose data from time to
キャッシュなので失っても大丈夫です
time because you'll just get it, you'll get the authoritative copy
データベースから原本のコピーを得られますから
out of the database. And this distribution of keys over multiple servers
複数のサーバに対するキーの分配は
is gnereally handled by the library. You know, sometimes you have to
通常ライブラリで扱われます
do it yourself. But most libraries and the Python library we'll be
自力で対処する場合もありますが 講義で使うPythonライブラリでは
using, and this class this abstracts all of this for you so
自動で作成してくれるので何もしなくて結構です
you don't have to deal with it. It's very common to actually
各マシン上で小規模のmemcachedサーバを
run a little memcache server on each machine, and then have each
起動させることはよくあることです
app server you know, communicate to all the caches. You kind of get
各APサーバがすべてのキャッシュを参照します
this big ball of this big ball of connections. But everything works
コネクションが複雑に入り組んでいてもうまく動きます
out okay so. And mem cache is a very simple protocol and
memcachedはプロトコルや運用方法がシンプルです
the operations it does are very simple. So, ultimately we're going to
結局のところ格納しているのは
be storing you know keys to values. Where the keys and
キーと値のペアです　キーと値は文字列で
values are both strings. And the operations look something like this.
関数は次のようになります
We've got set and this takes a key and a value. And
setコマンドはキーと値を利用します
we've got get, this takes a key and returns a value.
そしてgetはキーに対して値を返します
And we've got delete, which takes a key and deletes the key.
deleteコマンドはキーに対するキーを削除します
There are other operations and there are actually a few other
他にも関数はあり 別のパラメータを
parameters here. But these are the basic ones, and you can see
いくつか使うこともありますがこれが基本的な方法です
what these three main operations, set, get, and delete, we could
set、get、deleteの3つの関数を使うことによって
actually implement all of the caching we've been doing in ASCIIchan
今までのASCII Chanのキャッシングを実行できます
in a system that will scale a lot better than having,
ディクショナリ･キャッシュを使うシステムよりも
you know, just a dictionary in our process. It also means
はるかにうまくスケールできます memcachedを使うメリットは
that if, the advantage you get from using memcaches if our
プロセスが再起動しても
process restarts, we don't have an empty dictionary anymore, we have
空の辞書はないということです
our memcached and, and our content lives on. So, what I'd
コンテンツも生きています
like you to do first, is implement a fake version of memcached.
皆さんにまずやって欲しいのは フェイク版memcachedの実装です
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