Monitoring the state of MongoDB clusters and hosts

Data on cluster and host states are available in the management console. You can view them on the Monitoring tab of the cluster management page or in Yandex Monitoring.

Diagnostic information about cluster states is presented as graphs.

Chart update rate:

• Standard hosts and hosts with an increased RAM to vCPU ratio (memory-optimized): 15 seconds.
• Hosts with a guaranteed vCPU share under 100% (burstable): 150 seconds.

You can configure alerts in Yandex Monitoring to receive notifications about cluster failures. In Yandex Monitoring, there are two alert thresholds: Warning and Alarm. If the specified threshold is exceeded, you will receive alerts via the configured notification channels.

Monitoring cluster stateMonitoring cluster state

To view detailed information about the Managed Service for MongoDB cluster state:

1. Go to the folder page and select Managed Service for MongoDB.

2. Click the cluster name and open the Monitoring tab.

3. To get started with Yandex Monitoring metrics, dashboards, or alerts, click Open in Monitoring in the top panel.

The following charts will open on the page:

• Asserts total: Number of asserts triggered in the cluster.
• Average operation time per host: Average time of operation execution by each host (in microseconds).
• Average operations time on primary: Average operation execution time on primary replicas (in microseconds).
• Average operations time on secondaries: Average operation execution time on secondary replicas (in microseconds).
• CPU usage per host: vCPU utilization per host (as a ratio of the number of vCPU cores).
• CPU usage per host, top 5 hosts: 5 hosts with the highest vCPU utilization (%).
• Configured oplog size per host: Size of the oplog on each cluster host (in GB).
• Connections per host: Average number of connections to each host.
• Data size on primary, top 5 databases: Size of the five largest DBs on the primary replica (in bytes). The chart counts data without compression.
• Disk read per host, top 5 hosts: 5 hosts with the highest load on reading from the disk subsystem (bytes per second).
• Disk space usage per host, top 5 hosts: 5 hosts that take up the most disk space (two charts are displayed: in bytes and %). The chart counts data after compression.
• Disk usage per host, top 5 hosts: 5 hosts with the highest load on the storage I/O subsystem (bytes per second).
• Disk write per host, top 5 hosts: 5 hosts with the highest load on writing to the disk subsystem (kilobytes per second).
• Documents affected on primary: Average number of documents affected by queries on the primary replica.
• Documents affected on secondaries: Average number of documents affected by queries on all secondary replicas.
• Documents affected per host: Average number of documents affected by queries on each host.
• Hosts available for read: Number of hosts that accept read data queries.
• Hosts available for write: Number of hosts that accept write data queries.
• Index size on primary, top 5 indexes: Size of the five largest indexes on the primary replica (in bytes).
• Memory usage per host: Amount of RAM used by each host (in bytes).
• Memory usage per host, top 5 hosts: 5 hosts that use the most RAM (%).
• Network data received per host, top 5 hosts: 5 hosts with the highest network load on reading (kilobytes per second).
• Network data sent per host, top 5 hosts: 5 hosts with the highest network load on writing (kilobytes per second).
• Network usage per host, top 5 hosts: 5 hosts with the highest total network load (kilobytes per second).
• Open cursors total: Number of open cursors in the cluster.
• Oplog window: Time interval, for which replication data is stored in each host's oplog collection.
• Page faults per host: Number of page faults on each host.
• Queries on secondaries: Average number of queries of each type on secondary replicas.
• Queries on primary: Average number of each type of query on primary replicas.
• Read operations count, top 5 collections: 5 collections with the longest time spent in reads.
• Readers/writers active queue per host, top 5: Total size of the 5 largest queues for each host:
  • With read requests
  • With write requests
• Replicated queries: Average number of replicated queries in the cluster.
• Replication lag per host and write_concern wait: Replication lag on each host and waiting time for write confirmation (in seconds).
• Scan and order per host: Number of data sorts without index usage on each host.
• Scanned / returned: Shows the following ratios:
  • scanned_docs / returned_docs: Documents scanned to documents returned.
  • scanned_keys / returned_docs: Index keys scanned to documents returned.
• TTL indexes activity: Total number of TTL indexes.
• Total operations count on cluster: Total number of operations performed in the cluster.
• Total operations time on cluster: Total operation execution time in the cluster (in milliseconds).
• WiredTiger cache pages evicted on primary: Average number of memory pages evicted on the primary replica.
• WiredTiger cache state on primary: WiredTiger cache usage on the primary replica (in bytes).
• WiredTiger checkpoint time on primary: Time it takes to create WiredTiger checkpoints on the primary replica (in milliseconds).
• WiredTiger concurrent transactions on primary: Average number of parallel transactions on the primary replica.
• WiredTiger transactions state on primary: Average number of transactions on each level on the primary replica.
• Write conflicts per host: Number of write conflicts on each host.
• Write operations count, top 5 collections: 5 collections with the longest time spent in writes.

Monitoring the state of hostsMonitoring the state of hosts

To view detailed information about the state of individual Managed Service for MongoDB hosts:

1. Go to the folder page and select Managed Service for MongoDB.
2. Click the cluster name and select the Hosts → Monitoring tab.
3. Select the host from the drop-down list. You will see the host role (PRIMARY or SECONDARY) and type (MONGOCFG, MONGOD, MONGOINFRA, or MONGOS) next to the host name.

This page displays charts showing the load on an individual host in the cluster:

• CPU: Load on processor cores. As the load goes up, the Idle value goes down.
• Memory: Use of RAM, in bytes. At high loads, the value of the Free parameter goes down while those of other parameters go up.
• Disk bytes: Speed of disk operations (bytes per second).
• Disk IOPS: Number of disk operations per second.
• Network bytes: Speed of data exchange over the network, in bytes per second.
• Network packets: Number of packets exchanged over the network, per second.

Alert settings in Yandex MonitoringAlert settings in Yandex Monitoring

To have other cluster health indicators monitored automatically:

The recommended thresholds are as follows:

Metric	Parameter	Alarm	Warning
DB write availability	can_write	Equals 0	—
Replication delay	replset_status-replicationLag	180	30
Storage space used	disk.used_bytes	90% of the storage size	70% of the storage size

For the disk.used_bytes metric, the Alarm and Warning thresholds are only set in bytes. For example, the recommended values for a 100 GB disk are as follows:

• Alarm: 96,636,764,160 bytes (90%)
• Warning: 75,161,927,680 bytes (70%)

You can view the current storage size in the detailed information about the cluster. For a complete list of supported metrics, see the Monitoring documentation.

Monitoring the transition to read-only modeMonitoring the transition to read-only mode

To monitor storage usage on cluster hosts and get notifications when free space is about to run out:

1. Create an alert.

2. Add the disk.free_bytes status metric.

   To do this, create a query in the query builder:

   service=managed-mongodb → name=disk.free_bytes → host=* → resource_id=* → resource_type=cluster.

3. Set the alert threshold values in the alert settings:

   • Condition: Set the Less than or equals condition for the size of free disk space to trigger an alert.

     The recommended threshold values depending on the storage size are as follows:

     Storage size, GB	Alarm	Warning
     ⩽ 600	1G: 1 GB	1500M: 1.5 GB
     > 600	6G: 6 GB	10G: 10 GB

   • Advanced settings → Aggregation function: Select Minimum (a minimum metric value for the period).

Cluster state and statusCluster state and status

The State of a cluster shows the health of its hosts, while the Status shows whether the cluster is started, stopped, or is at an intermediate stage.

To view a cluster's state and status:

1. Go to the folder page and select Managed Service for MongoDB.
2. Hover over the indicator in the Availability column in the required cluster row.

Cluster statesCluster states

State	Description	Suggested actions
ALIVE	Cluster is operating normally.	No action is required.
DEGRADED	Cluster is not running at its full capacity: the state of at least one of the hosts is other than ALIVE.	Run the diagnostics: Go to the Hosts tab and see which hosts are not working. Go to the Operations tab and make sure all operations are completed. Make sure the cluster is not under maintenance. If you cannot find the cause yourself, contact support.
DEAD	The cluster is down: none of its hosts are running.	Make a support request stating the following: Cluster ID. IDs of the last operations performed on it. Time the cluster entered the DEAD state according to the availability charts.
UNKNOWN	Cluster state is unknown.	Make a support request stating the following: Cluster ID. IDs of the last operations performed on it. Time the cluster entered the UNKNOWN state according to the availability charts.

Cluster statusesCluster statuses

Status	Description	Suggested actions
CREATING	Preparing for the first launch	Wait a while and get started. The time it takes to create a cluster depends on the host class.
RUNNING	Cluster is operating normally	No action is required.
STOPPING	Stopping cluster	After a while, the cluster status will change to STOPPED and the cluster will be disabled. No action is required.
STOPPED	Cluster stopped	Start the cluster to get it running again.
STARTING	Starting the cluster that was stopped earlier	After a while, the cluster status will change to RUNNING. Wait a while and get started.
UPDATING	Updating the cluster status	After the update is completed, the cluster status will change to RUNNING. Wait a while and get started.
ERROR	An error occurred that does not allow the cluster to continue working	Run the initial diagnostics: Analyze the cluster monitoring charts and view the operations performed. Prepare a list of IDs of problem resources. If you cannot find the cause of the error yourself, contact support.
STATUS_UNKNOWN	Cluster is unable to determine its own status	Run the initial diagnostics: Analyze the cluster monitoring charts and view the operations performed. Prepare a list of IDs of problem resources. If you cannot find the cause of the error yourself, contact support.