[mongodb-dev] MongoDB 4.0.0-rc0 is released

['Kelsey Schubert' via mongodb-dev]

*MongoDB 4.0.0-rc0, the first release candidate of MongoDB 4.0, is out and
is ready for testing. This is the culmination of the 3.7.x development
series, and includes many exciting new features. Get up to speed on MongoDB
4.0 with the online course M040: New Features and Tools in MongoDB 4.0
<https://university.mongodb.com/courses/M040/about>Here are some of the
highlights:Multi-document ACID transactionsWith snapshot isolation and
all-or-nothing execution, transactions extend MongoDB ACID data integrity
guarantees to multiple documents across one or many collections. These feel
just like the transactions you are familiar with from relational databases,
are easy to add to any application that needs them, and do not impact the
performance of workloads that don’t require them. With multi-document
transactions it’s easier than ever for all developers to address a complete
range of use cases with MongoDB, while for many of them, simply knowing
that they are available will provide critical peace of mind. In MongoDB 4.0
transactions work across replica sets, and MongoDB 4.2 will support
transactions across sharded clusters.Snapshot Read Concernfind, aggregate,
count, distinct, and geoNear queries executed against a replica set within
a read-only transaction will operate against a single, isolated snapshot,
ensuring that a consistent view of the data is returned to the client,
irrespective of whether that data is being simultaneously modified by
concurrent operations.Non-Blocking Secondary Reads To ensure that reads
could not return data that was not in the same causal order as the primary
replica, MongoDB previously blocked secondary reads while oplog entries
were applied. MongoDB 4.0 avoids blocking by reading from a snapshot on the
secondary, improving read latencies and increasing throughput from the
replica set, while maintaining a consistent ordering of data. For replica
sets with a high write load, not having to wait for readers between
applying oplog batches allows for reduced replication lag and faster
confirmation of majority writes.Extensions to Change StreamsChange Streams
can now be configured track changes across an entire database or whole
cluster. Additionally, change streams now will return a cluster time
associated with an event, which can be used by the application to provide
an associated wall clock time for the event.Data Type ConversionsA $convert
expression has been added to the aggregation framework. This will not only
allow new ETL workloads and simplify app development, but also allow the
MongoDB BI Connector <https://www.mongodb.com/products/bi-connector> to
push down large amounts of work to MongoDB Server, unlocking significantly
improved performance for users of that tool.Improved Migrations
ThroughputSharded migrations are now up to 40% faster, so users can more
easily and quickly scale capacity elastically in response to changing
application demand as nodes are added and removed from sharded
clusters.SCRAM-SHA-256We’ve added support for SCRAM-SHA-256, allowing
individual users to store SHA-2 based credentials when security policies
disallow the use of SHA-1.Native TLSOn macOS and Windows, MongoDB now uses
the platform's native cryptography and TLS support, and no longer uses
OpenSSL. Additionally, the system certificate stores can be used to manage
certificates.Improved Sharded Operation ManagementOperators can now list
and kill queries running in a sharded cluster directly on a mongos node.
When a sharded query either encounters an operation-fatal error, or is
explicitly killed by an operator, on either mongos or any shard, the query
will be promptly terminated on all other shards in the cluster. See
SERVER-6496 <https://jira.mongodb.org/browse/SERVER-6496> for further
details.Slow Query Logging on mongosPreviously only available on mongod, we
now log operations which exceed a particular latency threshold on mongos,
enabling DBAs to more quickly identify problematic queries.Hybrid Cursor
CachingImprovements in cursor caching unlock up to 2x performance gains on
deployments running with a large number of collections, and enable
operations like dropping a collection to execute without causing any
performance degradation on other active collections.MongoDB 4.0 Release
Notes <http://docs.mongodb.org/master/release-notes/4.0> | Changelog
<https://jira.mongodb.org/issues/?jql=project%20in%20(SERVER%2CTOOLS%2CWT)%20AND%20resolution%3D%27Fixed%27%20and%20(fixversion%20in%20versionMatch(%223.7.%5B0-9%5D%22)%20or%20fixVersion%20%3D%203.4.0-rc0)>
| Downloads <https://www.mongodb.com/download-center>As always, please
engage with us: - Report any issues
<https://jira.mongodb.org/projects/SERVER/>- Join the conversation on
Twitter: @MongoDB <https://twitter.com/mongodb> #MongoDB40
<https://twitter.com/search?q=%23MongoDB40>- Meet our engineering team and
other MongoDB users at MongoDB World'18 <https://www.mongodb.com/world18>
(June 26-27)-- The MongoDB Team*