Full Time Diagnostic Data Capture
To help MongoDB engineers analyze server behavior, mongod and
mongos processes include a Full Time Diagnostic Data
Capture (FTDC) mechanism. FTDC is enabled by default. Due to its
importance in debugging deployments, FTDC thread failures are fatal and
stop the parent mongod or mongos process.
Behavior
Note
FTDC User Permissions on Windows
On Windows, to collect system data such as disk, cpu, and memory, FTDC requires Microsoft access permissions from the following groups:
Performance Monitor Users
Performance Log Users
If the user running mongod and mongos is not an administrator, add them to these groups to log
FTDC data. For more information, see the Microsoft documentation here.
FTDC periodically collects statistics produced by the following commands:
replSetGetStatus(mongodonly)collStatsfor thelocal.oplog.rscollection (mongodonly)connPoolStats(mongosonly)
Depending on the host operating system, the diagnostic data may include one or more of the following utilization statistics:
CPU utilization
Memory utilization
Disk utilization related to performance. FTDC does not include data related to storage capacity.
Network performance statistics. FTDC only captures metadata and does not capture or inspect any network packets.
Note
If the mongod process runs in a container, FTDC
reports utilization statistics from the perspective of the container
instead of the host operating system. For example, if a the
mongod runs in a container that is configured with RAM
restrictions, FTDC calculates memory utilization against the container's
RAM limit, as opposed to the host operating system's RAM limit.
FTDC collects statistics produced by the following commands on file rotation or startup:
FTDC Data Files
mongod processes store FTDC data files in a
diagnostic.data directory under the instances
storage.dbPath. All diagnostic data files are stored
under this directory. For example, given a dbPath
of /data/db, the diagnostic data directory would be
/data/db/diagnostic.data.
mongos processes store FTDC data files in a
diagnostic directory relative to the systemLog.path log
path setting. MongoDB truncates the logpath's file extension and
concatenates diagnostic.data to the remaining name. For example,
given a path setting of
/var/log/mongodb/mongos.log, the diagnostic data directory would be
/var/log/mongodb/mongos.diagnostic.data.
FTDC Privacy
FTDC data files are compressed and not human-readable. They inherit the same file access permissions as the MongoDB data files. Only users with access to FTDC data files can transmit the FTDC data.
MongoDB engineers cannot access FTDC data without explicit permission and assistance from system owners or operators.
FTDC data never contains any of the following information:
Samples of queries, query predicates, or query results
Data sampled from any end-user collection or index
System or MongoDB user credentials or security certificates
FTDC data contains certain host machine information such as
hostnames, operating system information, and the options or settings
used to start the mongod or
mongos. This information may be
considered protected or confidential by some organizations or
regulatory bodies, but is not typically considered to be Personally
Identifiable Information (PII). For clusters where these fields are
configured with protected, confidential, or PII data, please notify
MongoDB engineers before sending FTDC data to coordinate
appropriate security measures.
Details
You can view the FTDC source code on the
MongoDB Github Repository.
The ftdc_system_stats_*.ccp files specifically define any
system-specific diagnostic data captured.
FTDC Defaults
FTDC runs with the following defaults:
Data capture every 1 second
200MB maximum
diagnostic.datafolder size.
These defaults are designed to provide useful data to MongoDB engineers with minimal impact on performance or storage size. These values only require modifications if requested by MongoDB engineers for specific diagnostic purposes.
Disable FTDC
To disable FTDC, start up the mongod or
mongos with the
diagnosticDataCollectionEnabled: false option in the
setParameter settings of your configuration file:
setParameter: diagnosticDataCollectionEnabled: false
Disabling FTDC may increase the time or resources required when analyzing or debugging issues with support from MongoDB engineers. For information on MongoDB Support, visit Get Started With MongoDB Support.