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Diagnostic Commands

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  • buildInfo
  • collStats
  • connectionStatus
  • dbStats
  • explain
  • getLog
  • getMore
  • hostInfo
  • ping
  • whatsmyuri

For the buildInfo command, the response contains the following fields:

Field
Description
ok
Returns 1 for success or 0 for failure.
version
The MongoDB client compatibility version. This is the earliest version of the MongoDB client with which the Data Federation service is compatible.
versionArray
The MongoDB client compatibility version in array format.
dataLake.version
The version number of Data Federation.
dataLake.gitVersion
The git version of the Data Federation service.
dataLake.date
The build timestamp of the Data Federation service.
Example
{
"ok" : <return>,
"version" : "<version-number>",
"versionArray" : [
<number>,
<number>,
<number>,
<number>
],
"dataLake" : {
"version" : "<version-number>",
"gitVersion" : "<version-number>",
"date" : "<timestamp>"
}
}

For the collStats command, Atlas Data Federation omits the following fields in the response:

  • avgObjSize
  • capped
  • max
  • maxSize
  • wiredTiger
  • nindexes
  • totalIndexSize
  • indexSizes

Atlas Data Federation includes the following fields in the response. You can use these fields to verify what partitions are used to populate a collection, understand how recently the stats were computed, and determine if Atlas Data Federation truncated the output document.

Field
Description
partitions.format
The file format of the partition.
partitions.attributes
The filtering attributes of the partition.
partitions.count
The number of documents in the partition.
partitions.source
The S3 URL or Atlas cluster name, which contains the backing data of the partition.
partitions.size
The size, in bytes, of the partition.
partitionCount
The number of partitions.
avgPartitionSize
The average size of all partitions.
cacheMetadata
Contains information on how recently the stats were computed.
cacheMetadata.computeTime
The time in ISODate format when the computation for the stats started.
cacheMetadata.automaticRefreshInProgress
The flag that indicates if a background job is running now to refresh the cache.
truncated

The flag that indicates whether Atlas Data Federation enforced the maximum document size limit of 16MiB. The flag value can be one of the following:

  • true - if the output document size exceeded the limit and was therefore truncated to include only enough partitions that allowed the document to comply with the size limit. If true, the partitionCount and avgPartitionSize values that Atlas Data Federation returns may be smaller than the actual values.
  • false - if Atlas Data Federation returns the entire document.
Example
{
...
"partitionCount": <number of partitions>,
"avgPartitionSize": <average size of all partitions>,
"partitions": [
{
"format": <file format>,
"attributes": <filtering attributes>,
"count": <number of documents in partition>,
"source": <S3 url or Atlas cluster name>,
"size": <size, in bytes, of the partition>
},
...
],
"truncated": false,
"cacheMetadata": {
computeTime: ISODate("2021-07-25T15:10:33.513Z"),
automaticRefreshInProgress: false
},
...
}

Atlas Data Federation introduces an optional boolean parameter, sync, to bypass the cache and fetch the most recent storage statistics for a given collection. The following values are valid for the sync parameter:

  • true - to bypass the cache and return the most recent storage statistics
  • false - to return cached data

If the sync parameter is omitted, defaults to false.

Example
db.runCommand( {collStats: "<string>", sync: true|false} )

To learn more about the parameters supported by this command, see collStats.

For connectionStatus command, Atlas Data Federation returns information about the current connection, specifically the state of authenticated users and their available roles.

Note

Only one user can authenticate on a connection to a federated database instance at any given time. If a user authenticates and then runs the db.auth() command, Data Federation replaces the previous user's permissions with the new user's permissions.

The connectionStatus command shows only the newly authenticated user in the authenticatedUsers output field.

For dbStats command, Atlas Data Federation introduces an optional boolean parameter, sync, to bypass the cache and fetch the most recent storage statistics for a given database. The following values are valid for the sync parameter:

  • true - to bypass the cache and return the most recent storage statistics
  • false - to use the cached data also

If the sync parameter is omitted, defaults to false.

Example
db.runCommand( {dbStats: 1, sync: true|false} )

To learn more about the parameters supported by this command, see dbStats.

Atlas Data Federation command omits the followig fields in the response:

  • object
  • avgObjSize
  • fsUsedSize
  • fsTotalSize

The commands adds the following fields in the response. You can use these fields to determine whether the command returned stale data.

Field
Description
cacheMetadata
Contains information on how recently the stats were computed.
cacheMetadata.computeTime
The time in ISODate format when the computation for the stats started.
cacheMetadata.automaticRefreshInProgress
The flag that indicates if a background job is running now to refresh the cache.

For explain command, the data returned by explain documents the Data Federation query plan. The explain output differs from MongoDB in that it provides information about the data partitions used to satisfy the query.

The following commands can be explained in Data Federation:

  • aggregate()
  • count()
  • find()

Atlas Data Federation supports the following verbosity modes:

  • queryPlanner - provides information on the query plan.
  • queryPlannerExtended - provides detailed information on the query plan including information about the S3 objects, such as the S3 object names and sizes, that will be queried.

Atlas Data Federation doesn't support executionStats and allPlansExecution modes.

Example

The following example shows how to use the explain command to get information about the aggregate command, including detailed information on the query plan.

db.runCommand({ "explain": { "aggregate": "user", "verbosity": "queryPlannerExtended", "pipeline": [ ], "cursor": {} }})

When you run explain, Atlas Data Federation returns the following fields:

Output Field Name
Description
stats
Document that describes the number and total size of partitions that Atlas Data Federation might open for the query.
stats.size
Total size of partitions that Atlas Data Federation might open for the query.
stats.numberOfPartitions
Number of partitions that Atlas Data Federation might open for the query.
plan
Document that contains the query execution plan for the query. The document contains nested execution plan nodes, each of which is a document describing the plan node. The nested plan node documents contain internal description of Atlas Data Federation's query execution, and include various node kinds that are subject to change. Contact MongoDB support if you need more help with understanding the query plan.

For getLog command, Atlas Data Federation returns a successful response, but doesn't includes log data.

For getMore command, Atlas Data Federation returns subsequent batches of documents currently pointed to by a cursor, when used in conjunction with commands that return a cursor, e.g. find and aggregate.

For hostInfo command, Atlas Data Federation returns only the following subset of fields from the standard MongoDB response:

{
"ok" : <return>,
"system" : {
"currentTime" : ISODate("<timestamp>"),
"hostname" : "<hostname>",
"cpuAddrSize" : <number>,
"memSizeMB" : <number>,
"numCores" : <number>,
"cpuArch" : "<identifier>",
},
"os" : {
"type" : "<string>",
"name" : "<string>",
},
"extra" : { }
}

For ping command, Atlas Data Federation tests whether a server is responding to commands.

For whatsmyuri command, Atlas Data Federation returns the client IP address.

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