November 2021
Intermediate to advanced
410 pages
12h 1m
Chinese
Content preview from MongoDB权威指南（第3版）
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246
｜
第
14
章
$minKey
user17256
one-min-shards-rs0
user17256
user24515
user24515
user31775
user31775
user39034
user39034
user46294
user46294
user53553
user53553
user60812
user60812
user68072
user68072
user75331
user75331
user82591
user82591
user89851
user89851
user9711
user9711
$maxKey
one-min-shards-rs1
图 14-5：块均匀地分布在可用的分片上
注意块列表开始和结束处的键，即
$minKey
和
$maxKey
。
$minKey
可以被认为是“负无穷”。
这个值比
MongoDB
中的其他值都要小
。类似地，
$maxKey
相当于“正无穷”。它比任何其
他值都要大。因此，总是会在块范围中看到这两个“极值”。片键的值始终位于
$minKey
和
$maxKey
之间。这两个值实际上是
BSON
类型，不应该用在应用程序中，它们主要是供内
部使用的。如果希望在
shell
中引用它们，可以使用
MinKey
和
MaxKey
常量。
现在数据已经分布在多个分片上了，让我们尝试执行一些查询。首先，查询一个特定的用
户名：
> db.users.find({username: "user12345"})
{
"_id" : ObjectId("5a4fb11dbb9ce6070f377880"), ...
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