发布于 2015-09-14 14:56:51 | 115 次阅读 | 评论: 0 | 来源: 网络整理
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create
The create command explicitly creates a collection. The command
uses the following syntax:
{ create: <collection_name> }
To create a capped collection limited to 40 KB, issue command in
the following form:
{ create: "collection", capped: true, size: 40 * 1024 }
The options for creating capped collections are:
| Options: |
- capped – Specify true to create a capped collection.
- autoIndexId – Specify false to disable the automatic
index created on the _id field. Before
2.2, the default value for autoIndexId was
false. See _id Fields and Indexes on Capped Collections
for more information.
- size – The maximum size for the capped collection. Once a
capped collection reaches its max size, MongoDB will
drop old documents from the database to make way for
the new documents. You must specify a size
argument for all capped collections.
- max – The maximum number of documents to preserve in the
capped collection. This limit is subject to the
overall size of the capped collection. If a capped
collection reaches its maximum size before it contains
the maximum number of documents, the database will
remove old documents. Thus, if you use this option,
ensure that the total size for the capped collection
is sufficient to contain the max.
|
|---|
The db.createCollection() provides a wrapper function that
provides access to this functionality.
注解
This command obtains a write lock on the affected database and
will block other operations until it has completed. The write
lock for this operation is typically short lived; however,
allocations for large capped collections may take longer.