MongoDB 4.4 Community Edition: LTS version

{"t":{"$date":"2020-05-18T20:18:13.533+00:00"},"s":"I",  "c":"NETWORK",  "id":23015,   "ctx":"listener","msg":"Listening on","attr":{"address":"127.0.0.1"}}
{"t":{"$date":"2020-05-18T20:18:13.533+00:00"},"s":"I",  "c":"NETWORK",  "id":23016,   "ctx":"listener","msg":"Waiting for connections","attr":{"port":27001,"ssl":"off"}}

• Union aggregation pipeline stage to blend data from multiple collections for deeper exploration and analysis.
• Custom Aggregation Expressions to extend MongoDB with your own functions, executed as part of an aggregation pipeline.
• Global Read and Write Concerns to configure cluster-wide read isolation and write durability guarantees.
• New Rust and Swift drivers.

• Refinable Shard Keys to define and refine your shard keys at any time, with no system downtime.
• Compound Hashed Shard Keys that more evenly distribute load across shards without losing data locality.
• Hedged Reads minimize p95 and p99 latencies by submitting read requests to multiple replicas and returning results as soon as the quickest node responds.
• Simultaneous Indexing and Streaming Replication that reduce replica lag to serve fresher data to your users.

• Mirrored Reads that pre-warm the caches of secondary replicas to reduce the impact of primary elections following an outage or after planned maintenance.
• Resumable Initial Sync to make it easier and faster to scale-out when adding new replicas or recover nodes that have fallen too far behind the rest of the cluster.
• AWS IAM Authentication that simplifies cloud-native security by reusing existing regular and temporary Amazon IAM credentials when connecting to MongoDB Atlas.
• TLS 1.3 and 50% faster client authentication to MongoDB

• $indexStats has some new field outputs:
  • building a boolean flag, indicates that an index is being built
  • spec specification document for each index
  • shard the specific name of a shard, if required
• $merge has been improved to output on the same collection that is being upgraded ; in addition, one can also output in a collection that appears on the pipeline like the $lookup
• $planCacheStats state has been changed to run both mongod and mongos instances in MongoDB ; it has a new field: named host, when running mongo ; PlanCache.list() is a wrapper for $planCacheStats aggregation stage
• $collStats now accepts the query exec stats during augment documentation ; in addition, collection scans as fields with the following description:
  • nonTailble a 64-bit integer that performs a collection scan on several queries that do not use tailable cursor
  • total a collection of queries performed collection scan which does not use a tailable cursor
• $unionWith aggregation has been added ; it is new feature that unifies collection sets, that is, it unites results of a pipeline from several collections into one set ; it allows two type of syntax, as below:
  • $unionWith general syntax:

    cd{ $unionWith: { coll: "<collection>", pipeline: [ <stage1>, ... ] } }
    

  • $unionWith simplified version of syntax which is used to include all documents from a collection:

    { $unionWith: "<collection>" }  // include all documents from the specified collection
    

• $accumulator is another new feature that specifies a custom accumulator operator ; accumulators are operators that do not change state as documents make progress along the pipeline ; it can also be used to execute external JavaScript functions that are not supported by MongoDB ; it can be found in 3 stages of the pipeline:
  • $bucket stage: only outputs documents containing not less than one document input
  • $group stage: inputs documents by specified _id and outputs a document for each particular grouping
  • $bucketAuto stage: it sorts document entries into specific group numbers known as buckets
    The syntax for $accumulator is as follows:

    {
    	$accumulator:{
    		init: ,
    		initArgs: , // Optional
    		accumulate: ,
    		accumulateArgs: ,
    		merge: ,
    		finalize: , // Optional
    		lang:
    	}
    }
    

• $function aggregation: defines an aggregation function in JavaScript ; this operator can be used to define functions to use behaviors that are not supported by MongoDB
  See below the syntax for $function:

  {
  	$function: {
  		body: ,
  		args: ,
  		lang: "js"
  	}
  }
  

• Windows: x64
• MacOS: x64
• Debian Linux 9.2 / 10 / 11: x64
• Ubuntu Linux 18.04 / 20.04: x64, arm64
• Ubuntu Linux 16.04: x64
• RedHat Linux / CentOS Linux 8.2: arm64
• RedHat Linux / CentOS Linux 6.2+ / 7.0 / 8.0: x64
• SuSE Linux 12 / 15: x64
• Amazon Linux 2: x64, arm64
• Amazon Linux: x64