“In January of this year, we began looking into using Cell ID codes as an additional signal to further improve the speed and performance of message delivery,” the Google spokesperson said in an email. “However, we never incorporated Cell ID into our network sync system, so that data was immediately discarded, and we updated it to no longer request Cell ID.”
If they were “never used or stored”, why did they start collecting them in the first place? This is like a kid caught with their hand in the cookie jar saying they weren’t going to eat any cookies. Sure.
The amount of memory varies per implementation, but in the case of this implementation, we could count over 1 million IDs using just 12 kilobytes of space, which would be 0.15% of the original space usage!
維基百科上有說明當資料量在 109 這個等級時，用 1.5KB 的記憶體只有 2% 的誤差值：
The HyperLogLog algorithm is able to estimate cardinalities of > 109 with a typical error rate of 2%, using 1.5 kB of memory.
sudo-touchid is a fork of sudo with Touch ID support on macOS (powered by the LocalAuthentication framework). Once compiled, it will allow you to authenticate sudo commands with Touch ID in the Terminal on supported Macs (such as the late 2016 MacBook Pros).
Current releases of PostgreSQL need to read every page in the database at least once every 2 billion write transactions (less, with default settings) to verify that there are no old transaction IDs on that page which require "freezing".
All of a sudden, when the number of transaction IDs that have been consumed crosses some threshold, autovacuum begins processing one or more tables, reading every page. This consumes much more I/O bandwidth, and exerts much more cache pressure on the system, than a standard vacuum, which reads only recently-modified page.
而作者送了 patch 改成只會讀還沒搞定的部份：
Instead of whole-table vacuums, we now have aggressive vacuums, which will read every page in the table that isn't already known to be entirely frozen.
要注意的是，agreesive vacuum 相較於 vacuum 會多吃很多資源，但可以打散掉 (有點像一次大 GC 導致 lag 與多次 minor GC 讓程式反應時間變得比較順暢的比較)：
An aggressive vacuum still figures to read more data than a regular vacuum, possibly a lot more. But at least it won't read the data that hasn't been touched since the last aggressive vacuum, and that's a big improvement.
還是可以 opt-out 改回來，不過官方還是建議儘量用長的 ID 測試，因為今年年底將全面強迫使用：
We recommend testing longer IDs before transitioning; however, if you have not yet tested your systems for compatibility with the longer format, you still have the option to opt out and receive shorter IDs until early December 2016.