边写边转储
Mongodump while writing
运行 mongodump 对付 运行ning 服务器每秒有很多写入是否安全？是否有可能以这种方式损坏转储？
来自here：
Use --oplog to capture incoming write operations during the mongodump operation to ensure that the backups reflect a consistent data state.
是不是说无论写入多少次数据库dump都会保持一致？
如果我在凌晨 1 点 运行 mongodump --oplog 并在凌晨 2 点结束，那么我 运行 mongorestore --oplogReplay 我会得到什么状态？
来自here：
However, the use of mongodump and mongorestore as a backup strategy can be problematic for sharded clusters and replica sets.
但是为什么呢？我有 1 个主要副本集和 2 个辅助副本集。 运行 mongodump 有什么问题要反中二？它应该与主要相同（复制滞后差异除外）。
docs们说的很清楚了:
--oplog
Creates a file named oplog.bson as part of the mongodump output. The oplog.bson file, located in the top level of the output directory, contains oplog entries that occur during the mongodump operation. This file provides an effective point-in-time snapshot of the state of a mongod instance. To restore to a specific point-in-time backup, use the output created with this option in conjunction with mongorestore --oplogReplay.
Without --oplog, if there are write operations during the dump operation, the dump will not reflect a single moment in time. Changes made to the database during the update process can affect the output of the backup.
--oplog has no effect when running mongodump against a mongos instance to dump the entire contents of a sharded cluster. However, you can use --oplog to dump individual shards.
如果没有 --oplog，您仍然会得到一个有效的转储，只是有点不一致 - 凌晨 1 点到 2 点之间完成的一些写入将会丢失。
使用 --oplog，您可以在凌晨 2 点捕获 oplog 文件。转储仍然不一致，在恢复时重放操作日志修复了这个问题。
转储分片集群的问题值得dedicated page in the docs。本质上是因为同步所有节点的备份很复杂：
To create backups of a sharded cluster, you will stop the cluster balancer, take a backup of the config database, and then take backups of each shard in the cluster using mongodump to capture the backup data. To capture a more exact moment-in-time snapshot of the system, you will need to stop all application writes before taking the filesystem snapshots; otherwise the snapshot will only approximate a moment in time.
转储副本集没有问题。
运行 mongodump 对付 运行ning 服务器每秒有很多写入是否安全？是否有可能以这种方式损坏转储？
来自here：
Use
--oplogto capture incoming write operations during the mongodump operation to ensure that the backups reflect a consistent data state.
是不是说无论写入多少次数据库dump都会保持一致？
如果我在凌晨 1 点 运行 mongodump --oplog 并在凌晨 2 点结束，那么我 运行 mongorestore --oplogReplay 我会得到什么状态？
来自here：
However, the use of
mongodumpandmongorestoreas a backup strategy can be problematic for sharded clusters and replica sets.
但是为什么呢？我有 1 个主要副本集和 2 个辅助副本集。 运行 mongodump 有什么问题要反中二？它应该与主要相同（复制滞后差异除外）。
docs们说的很清楚了:
--oplogCreates a file named
oplog.bsonas part of the mongodump output. Theoplog.bsonfile, located in the top level of the output directory, contains oplog entries that occur during the mongodump operation. This file provides an effective point-in-time snapshot of the state of a mongod instance. To restore to a specific point-in-time backup, use the output created with this option in conjunction withmongorestore --oplogReplay.Without
--oplog, if there are write operations during the dump operation, the dump will not reflect a single moment in time. Changes made to the database during the update process can affect the output of the backup.
--oploghas no effect when running mongodump against a mongos instance to dump the entire contents of a sharded cluster. However, you can use--oplogto dump individual shards.
如果没有 --oplog，您仍然会得到一个有效的转储，只是有点不一致 - 凌晨 1 点到 2 点之间完成的一些写入将会丢失。
使用 --oplog，您可以在凌晨 2 点捕获 oplog 文件。转储仍然不一致，在恢复时重放操作日志修复了这个问题。
转储分片集群的问题值得dedicated page in the docs。本质上是因为同步所有节点的备份很复杂：
To create backups of a sharded cluster, you will stop the cluster balancer, take a backup of the config database, and then take backups of each shard in the cluster using mongodump to capture the backup data. To capture a more exact moment-in-time snapshot of the system, you will need to stop all application writes before taking the filesystem snapshots; otherwise the snapshot will only approximate a moment in time.
转储副本集没有问题。