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db.createCollection()¶
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Definition¶
-
db.
createCollection
(name, options)¶ Creates a new collection explicitly.
Because MongoDB creates a collection implicitly when the collection is first referenced in a command, this method is used primarily for creating new capped collections.
db.createCollection()
is a wrapper around the database commandcreate
.The
db.createCollection()
method has the following prototype form:The
db.createCollection()
method has the following parameters:Parameter Type Description name
string The name of the collection to create. options
document Optional. Configuration options for creating a capped collection or for preallocating space in a new collection. The
options
document creates a capped collection or preallocates space in a new ordinary collection. Theoptions
document contains the following fields:Field Type Description capped
boolean Optional. To create a capped collection, specify true
. If you specifytrue
, you must also set a maximum size in thesize
field.autoIndexId
boolean Optional. Specify
false
to disable the automatic creation of an index on the_id
field.Important
For replica sets, all collections must have
autoIndexId
set totrue
.size
number Optional. Specify a maximum size in bytes for a capped collection. Once a capped collection reaches its maximum size, MongoDB removes the older documents to make space for the new documents. The size
field is required for capped collections and ignored for other collections.max
number Optional. The maximum number of documents allowed in the capped collection. The size
limit takes precedence over this limit. If a capped collection reaches thesize
limit before it reaches the maximum number of documents, MongoDB removes old documents. If you prefer to use themax
limit, ensure that thesize
limit, which is required for a capped collection, is sufficient to contain the maximum number of documents.usePowerOf2Sizes
boolean Optional. Available for the MMAPv1 storage engine only.
Deprecated since version 3.0: For the MMAPv1 storage engine, all collections use the power of 2 sizes allocation unless the
noPadding
option istrue
. TheusePowerOf2Sizes
option does not affect the allocation strategy.noPadding
boolean Optional. Available for the MMAPv1 storage engine only.
New in version 3.0:
noPadding
flag disables the power of 2 sizes allocation for the collection. WithnoPadding
flag set to true, the allocation strategy does not include additional space to accommodate document growth, as such, document growth will result in new allocation. Use for collections with workloads that are insert-only or in-place updates (such as incrementing counters).Defaults to
false
.Warning
Do not set
noPadding
if the workload includes removes or any updates that may cause documents to grow. For more information, see No Padding Allocation Strategy.storageEngine
document Optional. Available for the WiredTiger storage engine only.
New in version 3.0.
Allows users to specify configuration to the storage engine on a per-collection basis when creating a collection. The value of the
storageEngine
option should take the following form:Storage engine configuration specified when creating collections are validated and logged to the oplog during replication to support replica sets with members that use different storage engines.
Examples¶
Create a Capped Collection¶
Capped collections have maximum size or document counts that prevent them from growing beyond maximum thresholds. All capped collections must specify a maximum size and may also specify a maximum document count. MongoDB removes older documents if a collection reaches the maximum size limit before it reaches the maximum document count. Consider the following example:
This command creates a collection named log
with a maximum size of 5
megabytes and a maximum of 5000 documents.
See Capped Collections for more information about capped collections.
Specify Storage Engine Options¶
New in version 3.0.
You can specify collection-specific storage engine configuration
options when you create a collection with
db.createCollection()
. Consider the following operation:
This operation creates a new collection named users
with a
specific configuration string that MongoDB will pass to the
wiredTiger
storage engine. See the WiredTiger documentation of
collection level options
for specific wiredTiger
options.