$k \leq n \leq 100000$,求式子$Ans=\sum_{i=1}^n w_i\sum_{j=1}^n j\binom{n-1}{n-j} \{ ^{n-j}_{k-1} \}$. 题解用了另一种角度考虑:一个$j$和$i$分到同一组,就对$i$有1的贡献.然后就变成$Ans=(\{ ^n_k\}+(n-1)\{^{n-1}_{k}\}) \sum_{i=1}^n w_i$. 还有一种理解$\sum_{j=1}^n j\binom{n-1}{n-j} \begin{Bmatrix…

Reference: http://blogs.msdn.com/b/felixmar/archive/2011/08/29/partitioning-amp-archiving-tables-in-sql-server-part-2-split-merge-and-switch-partitions.aspx In the 1st part of this post, I explained how to create a partitioned table using a partition…

Rotating partitions   You can use the ALTER TABLE statement to rotate any logical partition to become the last partition. Rotating partitions is supported for partitioned (non-universal) table spaces and range-partitioned table spaces, but not for pa…

This is a common question asked by many Kafka users. The goal of this post is to explain a few important determining factors and provide a few simple formulas. More Partitions Lead to Higher Throughput The first thing to understand is that a topic pa…

集群为了保证数据一致性,在同步数据的同时也会通过节点之间的心跳通信来保证对方存活.那如果集群节点通信异常会发生什么,系统如何保障正常提供服务,使用何种策略回复呢? rabbitmq提供的处理脑裂的方法有两种:autoheal.pause_minority. autoheal指的是在出现脑裂且恢复时采用分区中与客户端连接数最多的一个分区来作为winner,并将所有的losers分区重启. pause_miniroty指的是在出现脑裂后判断自己是否为众数者majority,即自己所在分区是否为总节点…

2013-05-01 Created By BaoXinjian…

why we need partitions The first and most demanding reason to use partitions in a database is to increase the performance of the database. This is achieved by partition-wise joins; if a user’s queries perform a lot of full-table scans, partitioning w…

[user@username home]$ lspci00:00.0 Host bridge: Intel Corporation 4th Gen Core Processor DRAM Controller (rev 06)00:01.0 PCI bridge: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor PCI Express x16 Controller (rev 06)00:14.0 USB controller: I…

概述:在Oracle数据库中,分区(partitioning)可以使非常大的表(table)或索引(index)分解为小的易管理的块(pieces),这些块被称作分区(partitions).每个分区都必须有相同的逻辑结构,如列名.数据类型.约束条件等,但是每个分区都可以都各自独立的物理结构. 分区的好处: 1.增加可用性: 2.易于模式对象的管理 3.减少在OLTP系统中对资源的争用 4.提高在数据仓库中查询的性能 分区键(Partition Key) 分区键是一或多个用来决定每一行去哪个分区…

Coin partitions Let p(n) represent the number of different ways in which n coins can be separated into piles. For example, five coins can separated into piles in exactly seven different ways, so p(5)=7. OOOOOOOOO OOOO OOOOO O OOO OO OOO O O OO O O O…