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Review Available Metrics

You can review the following metrics to monitor your database deployments.

Important

The metrics available depend on your user role and database deployment type.

Note

Currently, serverless instance metrics don't support any third-party monitoring services (for example, Datadog).

Metric
Description
Asserts

Displays the following information:

  • ASSERT_REGULAR displays the average rate of regular asserts raised per second over the selected sample period.
  • ASSERT_WARNING displays the average rate of warnings per second over the selected sample period.
  • ASSERT_MSG displays the average rate of message asserts per second over the selected sample period. These internal server errors have a well-defined text string. Atlas logs stack traces for these.
  • ASSERT_USER displays the average rate of user asserts per second over the selected sample period. This metric includes asserts that a user generates, such as out of disk space or duplicate key errors.

Monitor asserts to track how many errors occur while trying to read or write data. Check the server logs to identify the source of any errors.

Avg Object Size

Displays the average object size across all collections in the database.

Monitor object size to track the size of your objects and better understand your database space.

Cache Activity

Displays the following information:

  • readInto (replica set) or cache read into (sharded cluster) displays the rate in bytes per second of data read from disk into memory to service queries.
  • writtenFrom (replica set) or cache written from (sharded cluster) displays the rate in bytes per second of data written from memory into disk to service writes.

Monitor the MongDB cache, which stores frequently accessed data in memory to service queries faster.

Cache Usage

Displays the following information:

  • dirty (replica set) or cache dirty (sharded cluster) displays the total dirty bytes cached in memory for serving reads and writes.
  • used (replica set) or cache used (sharded cluster) displays the total bytes cached in memory for serving reads and writes.

These metrics include both indexes and data from the working set.

Sustained high cache usage indicates the RAM is too small for your workloads. Optimize your queries to avoid frequent disk reads. If write operations make cache usage high, throttle them.

Collections

Displays the number of collections in the database.

Monitor collections to determine restart times, continuous backup performance, and stability.

Connections (serverless instance/replica set) or connection (sharded cluster)

Displays the total number of active connections to the database deployment.

Monitor connections to determine whether the current connection limits are sufficient. If necessary, upgrade the cluster tier.

Cursors

Displays the following information:

  • totalOpen displays the number of cursors that the server maintains for clients.
  • totalTimedOut displays the average rate of cursors that have timed out per second over the selected sample period.

Monitor cursors to close unnecessary cursors and reduce the timeout configuration in the application.

DB Storage

Displays the following information:

  • storageSize (replica set) or db storage size (sharded cluster) displays the sum total amount of on-disk storage space allocated for document storage across all databases.
  • Data Size (serverless instance), dataSize (replica set), or db data size (sharded cluster) displays the amount of storage space in bytes that your stored data uses.

Monitor storage space to determine whether to use disk auto-scaling or manually increase the disk size. You can also monitor this metric to verify backup billing.

Disk IOPS

Displays input operations per second.

Monitor whether disk IOPS approaches the maximum provisioned IOPS. Determine whether the cluster can handle future workloads.

Disk Latency

Displays the following information:

  • Read displays the average amount of time to read from disk.
  • Write displays the average amount of time to write to disk.

Monitor disk latency to track the efficiency of reading from and writing to disk.

Disk Queue Depth

Displays the average length of the queue of requests issued to the disk partition that MongoDB uses.

Monitor disk queue depth to identify potential issues and bottlenecks.

Disk Space Free

Displays the total amount of free space remaining on disk.

Monitor free disk space to determine whether to use disk auto-scaling or manually increase the disk size.

Disk Space Percent Free

Displays the total amount of free space remaining on disk as a percentage of the total disk space.

Monitor the percentage of free disk space to determine whether to use disk auto-scaling or manually increase the disk size.

Disk Space Used

Displays the total space on disk used.

Monitor the used disk space to determine whether to use disk auto-scaling or manually increase the disk size.

Document Metrics

Displays the following information:

  • Returned displays the documents per second returned.
  • Inserted displays the documents per second inserted.
  • Updated displays the documents per second updated.
  • Deleted displays the documents per second deleted.

Monitor document metrics to measure the work MongoDB completes.

Execution Time

Displays the average time in seconds for the following metrics:

  • Average read operational latency
  • Average write operational latency
  • Average command operational latency

Monitor execution time for an increase in read operations to optimize queries and indexes.

Index Size

Displays the total size of all indexes in the database. This metric includes the overhead incurred by indexes on top of the actual document data on which the indexes are based.

Monitor the index size to manage your indexes. To learn more, see Indexing Strategies.

Indexes

Displays the total number of indexes in the database.

Monitor indexes to manage them. To learn more, see Indexing Strategies.

Locks

Displays the following information:

  • GLOBAL_LOCK_CURRENT_QUEUE_TOTAL displays the number of operations queued waiting for any lock.
  • GLOBAL_LOCK_CURRENT_QUEUE_READERS displays the number of operations queued waiting for a read lock.
  • GLOBAL_LOCK_CURRENT_QUEUE_WRITERS displays the number of operations waiting for a write lock.

Monitor locks to optimize queries.

Memory

Displays the total consumption of memory in megabytes at a particular point in time:

  • memory_resident (replica set) or memory resident (sharded cluster) displays the memory that the MongoDB process running on a node consumes. This metric excludes the consumption of other processes and does not represent the total memory that the node consumes.
  • memory_virtual (replica set) or memory virtual (sharded cluster) displays the memory reserved in disk to act as swap space.

Monitor memory to determine whether to upgrade to a higher cluster tier.

Network

Displays the following information:

  • bytesIn displays the average rate of physical bytes (after any wire compression) sent to this database server per second over the selected sample period.
  • bytesOut displays the average rate of physical bytes (after any wire compression) sent from this database server per second over the selected sample period.
  • numRequests displays the average rate of requests sent to this database server per second over the selected sample period.

Monitor network metrics to track network performance.

Normalized System CPU

Displays the CPU usage of all processes on the node, scaled to a range of 0-100% by dividing by the number of CPU cores.

Monitor CPU usage to determine whether data is retrieved from disk instead of memory.

Num Extent

Displays the total number of contiguously allocated chunks of data file space for the database.

Monitor this metric to better understand your database space.

Objects

Displays the number of objects in the database.

Monitor this metric to better understand your database space.

OpCounters

Displays the number of the following operations per second run on a MongoDB process since the process last started:

  • command (replica set) or cmd (sharded cluster)
  • query
  • insert
  • delete
  • update
  • getmore

Monitor MongoDB operations to validate performance issues related to high workloads. Confirm the type of operations responsible for the load.

OpCounters - Repl

Displays the following information:

  • command displays the average rate of replicated commands applied per second over the selected sample period.
  • insert displays the average rate of replicated inserts applied per second over the selected sample period.
  • delete displays the average rate of replicated deletes applied per second over the selected sample period.
  • update displays the average rate of replicated updates applied per second over the selected sample period.

Monitor MongoDB operations to validate performance issues related to high workloads. Confirm the type of operations responsible for the load.

Operation Execution Time

Displays the average time in milliseconds to execute the following operations:

  • avg ms/read (replica set) or execution time reads (sharded cluster)
  • avg ms/write (replica set) or execution time writes (sharded cluster)
  • avg ms/command (replica set) or execution time commands (sharded cluster)

Monitor execution time for an increase in read operations to optimize queries and indexes. Determine whether you need to upgrade your cluster tier.

Oplog GB/Hour

Displays the average rate in gigabytes of oplog data that the primary generates per hour.

Monitor oplog data to determine whether you have to increase the oplog size.

Page Faults

Displays the average rate of page faults on this process per second over the selected sample period. In non-Windows environments this applies to hard page faults only.

Monitor page faults to determine whether to increase your memory.

Query Executor

Displays the following information:

  • Index Items Scanned displays the number of index items scanned per second.
  • Documents Scanned displays the number of docmuents scanned per second.

Monitor the query executor to determine whether you have any inefficient queries.

Query Targeting

Displays the efficiency of read operations run on MongoDB:

  • Scanned Objects to Returned (replica set) or scanned objects / returned (sharded cluster) displays the number of documents scanned to return one document.
  • Scanned Keys to Returned (replica set) or scanned keys / returned (sharded cluster) displays the number of index keys scanned to return one document.

Monitor query targeting to determine read efficiency and optimize queries and indexes.

Replication Headroom

Displays the difference between the primary's replication oplog window and the secondary's replication lag.

Monitor replication headroom to determine whether the secondary might fall off the oplog.

Replication Lag

Displays the approximate number of seconds the secondary is behind the primary in write application.

Monitor replication lag to determine whether the secondary might fall off the oplog.

Scan and Order

Displays the number of operations per second returning results that required a sort in-memory.

Monitor this metric to identify whether your queries need indexes.

Tickets Available

Displays the following information:

  • Tickets Available Read displays the number of read tickets available to the WiredTiger storage engine. Read tickets represent the number of concurrent read operations allowed into the storage engine. When this value reaches zero, new read requests might queue until a read ticket becomes available.
  • Tickets Available Write displays the number of write tickets available to the WiredTiger storage engine. Write tickets represent the number of concurrent write operations allowed into the storage engine. When this value reaches zero, new write requests might queue until a write ticket becomes available.

Monitor the tickets available to see when read and write requests queue.

Util %

Displays the percentage of time that requests are issued to and serviced by disk. This metric includes requests from any process, not just MongoDB processes.

Monitor whether utilization is high. Determine whether to increase the provisioned IOPS or upgrade the cluster.

Views

Displays the number of views in the database.

Monitor views to help optimize your database.

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