Compatibility Changes in MongoDB 3.4
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The following 3.4 changes can affect the compatibility with older versions of MongoDB.
See also Release Notes for MongoDB 3.4.
Sharded Cluster Changes
shardsvr
Requirement
For a 3.4 sharded cluster, mongod
instances for the shards must explicitly specify its role as a shardsvr
, either via the configuration file setting sharding.clusterRole
or via the command line option --shardsvr
.
3.4 mongos
and Earlier Versions of mongod
Version 3.4 mongos
instances cannot connect to earlier versions of mongod
instances.
Removal for Configuration Options
MongoDB 3.4 removes the following configuration options from the mongos
:
sharding.chunkSize
configuration file setting and--chunkSize
command-line optionsharding.autoSplit
configuration file setting and--noAutoSplit
command-line option
Removal of Support for SCCC Config Servers
3.4 sharded clusters no longer support the use of mirrored (SCCC) mongod
instances as config servers. The use of SCCC config servers, deprecated in the 3.2 release, is no longer valid. Instead, deploy your config servers as a replica set (CSRS).
To upgrade your sharded cluster to version 3.4, the config servers must be running as a replica set.
To convert your existing config servers from SCCC to CSRS, see the MongoDB 3.4 manual Upgrade Config Servers to Replica Set .
Initial Sync and renameCollection
If a collection is renamed on the sync source while an initial sync is running, the initial sync process fails and restarts to avoid possible data corruption. See SERVER-26117 .
Operations that rename collections include:
renameCollection
command anddb.collection.renameCollection()
method.- Aggregation (
db.collection.aggregate()
method oraggregate
command) with the$out
stage. - Map-reduce (
db.collection.mapReduce()
method ormapReduce
command) with theout
option. convertToCapped
command.
As such, when upgrading from 3.2.11 or earlier versions to 3.4, initial syncs may start failing if they encounter renameCollection
operations.
In MongoDB versions 3.2.11 or earlier versions, initial sync process would proceed when encountering renameCollection
operations, which could potentially corrupt data. See SERVER-4941 .
Deprecated Operations
group
Mongodb 3.4 deprecates the following commands and mongo
shell methods:
group
command anddb.collection.group()
. Usedb.collection.aggregate()
ordb.collection.mapReduce()
instead.
aggregate
without cursor
MongoDB 3.6 removes the use of aggregate
command without the cursor
option unless the command includes the explain
option. Unless you include the explain
option, you must specify the cursor option.
To indicate a cursor with the default batch size, specify cursor: {}
.
To indicate a cursor with a non-default batch size, use cursor: { batchSize: <num> }
.
Stricter Validation of Collection and Index Specifications
Stricter Validation of Collection Options
MongoDB 3.4 enforces a stricter validation of collection options during create
and db.createCollection()
operations; namely, the specified options must be valid options supported by create
and db.createCollection()
.
For example, the following operation is no longer valid:
Stricter Validation of Index Specifications
MongoDB 3.4 enforces a stricter validation of index specification during createIndexes
and db.collection.createIndex()
operations. The enforcement does not apply to existing indexes.
Stricter validation include the following:
Ensuring that the value in the index key pattern
key: value
is valid. Specifically, value can be:Value Description A number greater than 0 For ascending index A number less than 0 For descending index String “text”, “2dsphere”, “2d”, or “hashed” For special index types For example, the following operations are no longer valid:
Ensuring that the specified index options are valid. Previous versions ignored invalid options. For example, the following operations are no longer valid:
General Compatibility Changes
Updates to namespace restrictions: in MongodDB 3.4, the
$
character is no longer supported in database names.Important
You must drop any databases that contain a
$
in its name before upgrading to MongoDB 3.4.Removal of deprecated
textSearchEnabled
parameter. Starting from version 2.6, MongoDB enables the text search feature by default.Removal of
mongosniff
. In MongoDB 3.4,mongosniff
is replaced bymongoreplay
, which offers a more flexible superset ofmongosniff
’s functionality.Updates to
$project
specification behavior: empty documents in$project
specifications produce an error.If you include a
hint()
that specifies a sparse index when you perform a