標籤:列印new Date(),Fri Aug 12 13:37:51 CST 2016. 顯示Asia/Shanghai的時區,但是date toString 的時區簡寫卻是CST。更坑爹的是,Google CST結果出來是Central Standard Time. 表示North American Central Standard Time. 還以為jdk的date類有問題,debug date toString發現確實是將Asia/Shanghai的name 簡寫成CST.
標籤:elasticsearch mongodb hadoop An interesting trend has been developing in the IT landscape over the past few years. Many new technologies develop and immediately latch onto the “Big Data”
下面的例子是在小資料下測試的,我嘗試在單機的千萬層級測試,等很久都沒結果... 資料有表:crawler.videos,表結構是: _id, playUrl, siteId...只有_id是有索引的,siteId不同的值分別代表不同的網站。值有:1,2,3三個值。現在要統計資料庫中每個網站的所含有的id數。就是相當於在mySql中select count(_id),siteId from videos group by siteId 的語句。以siteId分組,統計各siteId所含有的id數。
前段時間串講的時候mongoDB中的DBRef這個東西沒有講太明白,由於時間原因就匆匆帶過了。在這裡附上一個小實驗,補充一下。As MongoDB is non-relational (no joins), references (”foreign keys”) between documents are generally resolved client-side by additional queries to the server.A DBRef is a reference from