省頻寬的方法:終極版本...

看到「Three ways to reduce the costs of your HTTP(S) API on AWS」這邊介紹在 AWS 上省頻寬費用的方法,看了只能一直笑 XD

第一個是降低 HTTP response 裡沒有用到的 header,因為每天有五十億個 HTTP request,所以只要省 1byte 就是省下 USD$0.25/day:

Since we would send this five billion times per day, every byte we could shave off would save five gigabytes of outgoing data, for a saving of 25 cents per day per byte removed.

然後調了一些參數後省下 USD$1,500/month:

Sending 109 bytes instead of 333 means saving $56 per day, or a bit over $1,500 per month.

第二個是想辦法在 TLS 這邊下手,一開始其中一個方向是利用 TLS session resumption 降低第二次連線的成本,但他們發現沒有什麼參數可以調整:

One thing that reduces handshake transfer size is TLS session resumption. Basically, when a client connects to the service for the second time, it can ask the server to resume the previous TLS session instead of starting a new one, meaning that it doesn’t have to send the certificate again. By looking at access logs, we found that 11% of requests were using a reused TLS session. However, we have a very diverse set of clients that we don’t have much control over, and we also couldn’t find any settings for the AWS Application Load Balancer for session cache size or similar, so there isn’t really anything we can do to affect this.

所以改成把 idle 時間拉長 (避免重新連線):

That leaves reducing the number of handshakes required by reducing the number of connections that the clients need to establish. The default setting for AWS load balancers is to close idle connections after 60 seconds, but it seems to be beneficial to raise this to 10 minutes. This reduced data transfer costs by an additional 8%.

再來是 AWS 本身發的 SSL certification 太肥,所以他們換成 DigiCert 發的,大幅降低憑證本身的大小,反而省下 USD$200/day:

So given that the clients establish approximately two billion connections per day, we’d expect to save four terabytes of outgoing data every day. The actual savings were closer to three terabytes, but this still reduced data transfer costs for a typical day by almost $200.

這些方法真的是頗有趣的 XDDD

不過這些方法也是在想辦法壓榨降低與 client 之間的傳輸量啦,比起成本來說反而是提昇網路反應速度...

Hacker News

早上看到「Tell HN: Thank you for not redesigning Hacker News」這篇,作者在網路速度受限的地區,上各種網站幾乎都不會動,但 Hacker News 沒有改用一堆前端框架,而是保留使用 HTML 反而讓頁面維持極小:

I’m currently in a country with low speed internet and the entire ‘modern’ web is basically unusable except HN, which still loads instantly. Reddit, Twitter, news and banking sites are all painfully slow or simply time out altogether.

To PG, the mods and whoever else is responsible: thank you for not trying to ‘fix’ what isn’t broken.

順手開了一下網路工具來看,發現單一元件最大的居然是 favicon XDDD:

Wikipedia 上列出來的相容性,如果只支援 IE11+ 的話,看起來可以改用 PNG,大小就已經有明顯的改善了:

-rw-r--r-- 1 gslin staff 7527 Sep  2 09:50 favicon.ico
-rw-r--r-- 1 gslin staff 2598 Sep  2 09:51 favicon.png

RFC8482 廢掉 DNS 查詢的 ANY query 了...

看到 Cloudflare 的「RFC8482 - Saying goodbye to ANY」這篇,裡面提到 RFC8482 廢掉了 ANY 查詢:「Providing Minimal-Sized Responses to DNS Queries That Have QTYPE=ANY」。

The Domain Name System (DNS) specifies a query type (QTYPE) "ANY". The operator of an authoritative DNS server might choose not to respond to such queries for reasons of local policy, motivated by security, performance, or other reasons.

對 Cloudflare 的痛點主要在於營運上的困難,因為 ANY 回應的 UDP packet size 很大,很容易造成放大攻擊:

把拒絕 ANY 查詢變成標準後,讓 DNS provider 手上多了一把武器可以用。

MySQL 8.0 的 innodb_dedicated_server

Percona 介紹了 MySQL 8.0 將會推出的 innodb_dedicated_server 參數:「New MySQL 8.0 innodb_dedicated_server Variable Optimizes InnoDB from the Get-Go」,Oracle 官方的文件在「15.6.13 Enabling Automatic Configuration for a Dedicated MySQL Server」這邊可以翻到。

這是針對整台機器完全給 MySQL 用的情況所設計的參數。在這種情況下,可以透過 RAM 的大小以及一些簡單的公式,得到還算堪用的系統參數...

依照說明,可以看到系統會依照記憶體的大小自動計算出 innodb_buffer_pool_sizeinnodb_log_file_size 這兩個參數,並且把 innodb_flush_method 設為 O_DIRECT_NO_FSYNC (如果所在平台有支援這個值)。

不過看了一下公式,依照經驗可以設的更積極一點... 像是 Percona 文章裡提到的,當記憶體夠大時,其實可以考慮從 80% 開始調整大小 (innodb_buffer_pool_size):

For InnoDB buffer pool size (based on this article), consider allocating 80% of physical RAM for starters. You can increase it to as large as needed and possible, as long as the system doesn’t swap on the production workload.

innodb_log_file_size 則應該要分析寫入的 pattern 而不是直接看 RAM 大小。有些機器雖然很大台但幾乎沒有寫入的量,照著公式的值就偏大很多:

For InnoDB log file size, it should be able to handle one hour of writes to allow InnoDB to optimize writing the redo log to disk. You can calculate an estimate by following the steps here, which samples one minute worth of writes to the redo log. You could also get a better estimate from hourly log file usage with Percona Monitoring and Management (PMM) graphs.

不過基本上 tune 出來的值還算堪用,對於剛入手的人頗有幫助。

Ubuntu 18.04 LTS Minimal Image 的大小

看到「RFC: Ubuntu 18.04 LTS Minimal Images」這篇,在蒐集將來要出的 Ubuntu 18.04 LTS Minimal Image 的意見...

The Ubuntu Minimal Image is the smallest base upon which a user can apt install any package in the Ubuntu archive.

雖然應該還會有改變,不過以目前的版本來看,可以看出壓縮前後兩種版本都比 16.04 小了不少:

對需要這些 image 的人來說 (像是當作 Docker 的 base image),小一點操作起來也比較開心...

Working Set Size (WSS) 的想法

NetflixBrendan Gregg (他比較知名的發明是 Flame Graph) 寫了一篇「How To Measure the Working Set Size on Linux」,他想要量測單位時間內會用到的記憶體區塊大小:

The Working Set Size (WSS) is how much memory an application needs to keep working. Your app may have populated 100 Gbytes of main memory, but only uses 50 Mbytes each second to do its job. That's the working set size. It is used for capacity planning and scalability analysis.

這可以拿來分析這些應用程式是否能夠利用 L1/L2/L3 cache 大幅增加執行速度,於是就可以做成圖,像是這樣:

在 Netflix 這樣人數的公司,需要設計一些有用的指標,另外發展出對應的工具,讓其他人更容易迅速掌握狀況,畢竟不是每個人都有上天下海的能力,遇到狀況可以馬上有頭緒進行 trouble shooting...

基於 RNN 的無損壓縮

Hacker News 上看到「DeepZip: Lossless Compression using Recurrent Networks」這篇論文,利用 RNN 幫助壓縮技術壓的更小,而程式碼在 GitHubkedartatwawadi/NN_compression 上有公開讓大家可以測試。

裡面有個比較特別的是,Lagged Fibonacci PRNG 產生出來的資料居然有很好的壓縮率,這在傳統的壓縮方式應該都是幾乎沒有壓縮率...

整體的壓縮率都還不錯,不過比較的對象只有 gzip,沒有拿比較先進的壓縮軟體進行比較) 像是 xz 之類的),看數字猜測在一般的情況下應該不會贏太多,不過光是 PRNG 那部份,這篇論文等於是給了一個不同的方向讓大家玩...

Amazon RDS 支援更大的硬碟空間與更多的 IOPS

Amazon RDS 的升級:「Amazon RDS Now Supports Database Storage Size up to 16TB and Faster Scaling for MySQL, MariaDB, Oracle, and PostgreSQL Engines」。

空間上限從 6TB 變成 16TB,而且可以無痛升。另外 IOPS 上限從 30K 變成 40K:

Starting today, you can create Amazon RDS database instances for MySQL, MariaDB, Oracle, and PostgreSQL database engines with up to 16TB of storage. Existing database instances can also be scaled up to 16TB storage without any downtime.

The new storage limit is an increase from 6TB and is supported for Provisioned IOPS and General Purpose SSD storage types. You can also provision up to 40,000 IOPS for Provisioned IOPS storage volumes, an increase from 30,000 IOPS.

不過隔壁的 Amazon Aurora 還是大很多啊 (64TB),而且實際上不用管劃多大,他會自己長大:

Q: What are the minimum and maximum storage limits of an Amazon Aurora database?

The minimum storage is 10GB. Based on your database usage, your Amazon Aurora storage will automatically grow, up to 64 TB, in 10GB increments with no impact to database performance. There is no need to provision storage in advance.

Microsoft 與 GitHub 合作,將會把 GVFS 移植到 Linux 與 Mac 上

MicrosoftGitHub 合作將本來只有在 Windows 上可以用的 GVFS 移植到 LinuxMac 上:「Microsoft and GitHub team up to take Git virtual file system to macOS, Linux」。

GVFS 是解決微軟內部自己在用 Git 的痛處,因為微軟的 repository 都... 有... 點... 肥... (畢竟有不少產品發展了很久)。

目前 Git 的操作是卡在 I/O 與 memory cache 的限制上:

Also, Git wasn't designed for a codebase that was so large, either in terms of the number of files and version history for each file, or in terms of sheer size, coming in at more than 300GB. When using standard Git, working with the source repository was unacceptably slow. Common operations (such as checking which files have been modified) would take multiple minutes.

GVFS 的想法是有用到的部份再真的去拉,藉此大幅減少 I/O 需求...

Twitter Moments 很大?

看到「How big is Twitter Moments?」這篇,在談 Twitter Moments

依照推算,Twitter Moments 的使用量應該比全世界任何一個媒體都大,但你會發現實際上沒有音量。沒有人談論他,沒有人引用他... 但估算起來他應該是超級大的產品?

有種「到底怎麼樣才算是一個成功的產品」的反思。