cookqq博客的列表

cookqq ›博客列表

mongostat-Failed: error connecting to db server: no reachable servers: Failed: error connecting to db server: no reachable serversmongodb没有部署副本集的时候执行mongostat查看mongodb状态的时候没有问题。最近将mongodb部署成了副本集，再次执行mongostat的时候，就报错了。解决办法指定要查看mongodb的ip

如何设置android studio让程序运行在真机中: 点击菜单栏的“Run”->“Edit Configurations...”。然后会打开Run/Debug Configuration窗口。在窗口右侧找到“target device”部分，勾选“USB device”前面的单选框。点击“ok”。

Deploy a Replica Set部署副本集: Three member replica sets provide enough redundancy冗余 to survive 生存most network partitions and other system failures. These sets also have sufficient capacity 充足能力 for many distributed read operations. Replica sets should always have an odd number of members副本集应该总是有一个奇数的成员. This ensures that elections will proceed smoothly 顺利. For more about designing replica sets, see the Replication overview.

使用BigDecimal保留小数点位数不对: 数据格式化1.545使用下面方法格式化结果是1.54，这个四舍五入的结果不对啊。发现BigDecimal bg = new BigDecimal(d)，bg值是1.544999999999999. 2位四舍五入结构是1.54.这不科学啊。

mongodb Create a User Administrator: use admindb.createUser( { user: "siteUserAdmin", pwd: "password", roles: [ { role: "userAdminAnyDatabase", db: "admin" } ] })

Deploy a Replica Set for Testing and Development单机器测试副本集: 在一台电脑测试副本集，副本集成员开启不同的端口号27017，设置不同的mongodb数据路径

Read Preference: By default, an application directs its read operations to the primary member in a replica set. Because write operations are issued to the single primary, reading from the primary returns the latest version of a document[1]. For an application that does not require fully up-to-date data, you can improve read throughput or reduce latency by distributing some or all reads to secondary members of the replica set.

Write Concern for Replica Sets: For a replica set, the default write concern confirms write operations only on the primary. You can, however, override this default write concern, such as to confirm write operations on a specified number of the replica set members.

Replica Set Read and Write Semantics: Users may configure read preference on a per-connection basis to prefer that the read operations return results from the secondary members. If clients configure the read preference to permit 许可证secondary reads, read operations can return data from secondary members that have not replicated more recent write operations 没有复制的最近的写操作

Rollbacks During Replica Set Failover: Rollback Limitations 大于300M数据，您必须手动介入以恢复数据

Factors and Conditions that Affect Elections影响选举的因素和条件: Heartbeats心跳 10s Priority Comparisons优先级比较 Network Partitions网络分区

Three Member Replica Sets: The minimum architecture of a replica set has three members. A three member replica set can have either three members that hold data, or two members that hold data and an arbiter.

Replica Set Deployment Architectures: The architecture of a replica set affects the set’s capacity and capability. This document provides strategies for replica set deployments and describes common architectures. The standard replica set deployment for production system is a three-member replica set. These sets provide redundancy and fault tolerance. Avoid complexity when possible, but let your application requirements dictate the architecture.

Replica Set Arbiter: 只能把arbiter 增加到偶数个成员的副本集，如果你把arbiter 增加到奇数成员的副本集中，可能造成捆绑选举，造成选择不出primary副本集。

Delayed Replica Set Members: Delayed members contain copies of a replica set’s data set. However, a delayed member’s data set reflects an earlier, or delayed, state of the set. For example, if the current time is 09:52 and a member has a delay of an hour, the delayed member has no operation more recent than 08:52.

Replica Set Members 副本集成员介绍: Primary. 主副本 The primary receives all write operations. 提供所有写操作 Secondaries. 次副本 Secondaries replicate operations from the primary to maintain an identical data set. Secondaries may have additional configurations for special usage profiles. For example, secondaries may be non-voting orpriority 0. You can also maintain 保持 an arbiter as part of a replica set. Arbiters do not keep a copy of the data . However, arbiters play a role in the elections that select a primary if the current primary is unavailable. Arbiters 不保持数据，当主副本不能工作时候，Arbiters 作为选举（主副本）角色

Mongo Replication Introduction副本集介绍: Replication provides redundancy and increases data availability. With multiple copies of data on different database servers, replication protects a database from the loss of a single server. Replication also allows you to recover from hardware failure and service interruptions. With additional copies of the data, you can dedicate one to disaster recovery, reporting, or backup.随着数据的附加副本，您可以将一个灾难恢复

一键分享文章