月份: 2010 年 7 月

Android 會突然發出個聲音, 來通知說有新信 ... 等等的訊息.

不過, 我的使用有遇到下述幾種狀況:

• 通知聲音 很難聽 (可以換聲音, 但是我懶得去試哪個聲音好聽)
• 信件太多, 如果每次叫都去看, 會叫個不停
• 通常信件都不是急件, 不需要即時通知 (急件都直接打電話了)

閱讀全文〈Android 關閉通知音效〉

Memcached 是業界非常常用到的 cache system, 儲存格式是 key-value.

官方網站: Memcached: Free & open source, high-performance, distributed memory object caching system.

註：查看設定可用：$ echo "stats settings" | nc localhost 11211 # 看目前在跑得設定值

但是 Memcached 要知道的兩點:

1. Ram 要夠大, 因為 Memcached 的資料都塞在 Ram 裡面, Ram 不夠大, 新的資料就寫不進去.
2. Memcached 預設 單筆 資料儲存最大容量是 1M byte, 詳見 FAQ. (下述轉載此問題的問答)
   

   Q: What is the maximum data size you can store? (1 megabyte)

   • The maximum size of a value you can store in memcached is 1 megabyte. If your data is larger, consider clientside compression or splitting the value up into multiple keys.

為何是 1M, 是否可以增加, FAQ 也有答案:

• Memcached 最小值是 400 bytes, 最大值是 1M byte.
• 如果要超過 1M 也可以, 只是需要重新 compile memcached, 並且去修改 POWER_BLOCK 的值 或 使用 inefficient malloc/free 當 backend.

下述轉載此問題的問答:

Q: Why are items limited to 1 megabyte in size?

• Ahh, this is a popular question!
• Short answer: Because of how the memory allocator's algorithm works.
• Long answer: Memcached's memory storage engine (which will be pluggable/adjusted in the future...), uses a slabs approach to memory management. Memory is broken up into slabs chunks of varying sizes, starting at a minimum number and ascending by a factorial up to the largest possible value.
• Say the minimum value is 400 bytes, and the maximum value is 1 megabyte, and the factorial is 1.20:
• slab 1 - 400 bytes slab 2 - 480 bytes slab 3 - 576 bytes ... etc.
• The larger the slab, the more of a gap there is between it and the previous slab. So the larger the maximum value the less efficient the memory storage is. Memcached also has to pre-allocate some memory for every slab that exists, so setting a smaller factorial with a larger max value will require even more overhead.
• There're other reason why you wouldn't want to do that... If we're talking about a web page and you're attempting to store/load values that large, you're probably doing something wrong. At that size it'll take a noticeable amount of time to load and unpack the data structure into memory, and your site will likely not perform very well.
• If you really do want to store items larger than 1MB, you can recompile memcached with an edited slabs.c:POWER_BLOCK value, or use the inefficient malloc/free backend. Other suggestions include a database, MogileFS, etc.

註：2015/8 更新：Memcached 可以用 -I 5m 調整最大值。-I 5m 就是設定最大可以塞 5M 的資料。

相關網頁

• 15.6.2 Using memcached