Performance diagnostics in Managed Service for MongoDB

Managed Service for MongoDB provides a built-in tool for DBMS cluster performance diagnostics. Use it to analyze MongoDB profiling and index metrics.

Enabling statistics collectionEnabling statistics collection

To use the diagnostics tool, enable statistics collection when creating a cluster or updating its settings. By default, statistics are only collected for queries longer than 300 ms. If required, in DBMS settings, change the time threshold for collecting slow query statistics in the slowOpThreshold parameter.

Getting profiling dataGetting profiling data

For read/write and some other DB queries (such as aggregate), you can view the data collected by the MongoDB profiler:

• A chart with metrics for the selected data segment. You can hide or show individual categories in the chart by clicking on the category name in the chart legend.
• Table with statistics by query type.

To get data:

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

2. Click the cluster name and select the Performance diagnostics → Profiling tab.

3. Specify the time interval and, if necessary, set filters.

4. Select:

   • Data segment:
     • FORM: By query type
     • HOSTNAME: By shard PRIMARY host
     • NAMESPACE: By collection name
     • SHARD: By shard
     • USER: By user
   • Data grouping parameter:
     • COUNT: Number of queries.
     • DOCUMENTS_EXAMINED: Number of the collection documents scanned when executing the query.
     • DOCUMENTS_RETURNED: Number of returned documents.
     • DURATION: Query execution duration.
     • KEYS_EXAMINED: Number of index keys scanned when executing the query.
     • RESPONSE_LENGTH: Size of the document returned as a result of the query.
   • Aggregation function of the selected parameter:
     • AVG: Average value
     • SUM: Sum

For more information about what statistics you can get, see the MongoDB documentation.

Getting information about indexesGetting information about indexes

You can get collection access statistics for queries and recommendations for creating indexes of certain fields to speed up query processing.

1. Go to the folder page and select Managed Service for MongoDB.
2. Click the cluster name and select the Performance diagnostics → Suggested indexes tab.
3. Specify the time interval and, if necessary, set filters.

The table shows the fields to create indexes for and the number of times the collections were queried.