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Troubleshoot issues with diagnostics queries

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APPLIES TO: NoSQL MongoDB Cassandra Gremlin Table

In this article, we cover how to write simple queries to help troubleshoot issues with your Azure Cosmos DB account using diagnostics logs sent to AzureDiagnostics (legacy) and Resource-specific (preview) tables.

For Azure Diagnostics tables, all data is written into one single table and users need to specify which category they'd like to query.

For resource-specific tables, data is written into individual tables for each category of the resource (not available for table API). We recommend this mode since it makes it much easier to work with the data, provides better discoverability of the schemas, and improves performance across both ingestion latency and query times.

Common queries

Here's a list of common troubleshooting queries.

Query for operations that are taking longer than 3 milliseconds to run

Find operations that have a duration greater than 3 milliseconds.

AzureDiagnostics 
| where toint(duration_s) > 3 and ResourceProvider=="MICROSOFT.DOCUMENTDB" and Category=="DataPlaneRequests" 
| summarize count() by clientIpAddress_s, TimeGenerated

Query for user agents that are running operations

Find user agents associated with each operation.

AzureDiagnostics 
| where ResourceProvider=="MICROSOFT.DOCUMENTDB" and Category=="DataPlaneRequests" 
| summarize count() by OperationName, userAgent_s

Query for long-running operations

Find operations that ran for a long time by binning their runtime into five-second intervals.

AzureDiagnostics 
| where ResourceProvider=="MICROSOFT.DOCUMENTDB" and Category=="DataPlaneRequests" 
| project TimeGenerated , duration_s 
| summarize count() by bin(TimeGenerated, 5s)
| render timechart

Get partition key statistics to evaluate skew across top three partitions for a database account

Measure skew by getting common statistics for physical partitions.

AzureDiagnostics 
| where ResourceProvider=="MICROSOFT.DOCUMENTDB" and Category=="PartitionKeyStatistics" 
| project SubscriptionId, regionName_s, databaseName_s, collectionName_s, partitionKey_s, sizeKb_d, ResourceId

Get the request charges for expensive queries

Measure the request charge (in RUs) for the largest queries.

AzureDiagnostics
| where ResourceProvider=="MICROSOFT.DOCUMENTDB" and Category=="DataPlaneRequests" and todouble(requestCharge_s) > 10.0
| project activityId_g, requestCharge_s
| join kind= inner (
AzureDiagnostics
| where ResourceProvider =="MICROSOFT.DOCUMENTDB" and Category == "QueryRuntimeStatistics"
| project activityId_g, querytext_s
) on $left.activityId_g == $right.activityId_g
| order by requestCharge_s desc
| limit 100

Find which operations are taking most RU/s

Sort operations by the amount of RU/s they're using.

AzureDiagnostics
| where ResourceProvider=="MICROSOFT.DOCUMENTDB" and Category=="DataPlaneRequests"
| where TimeGenerated >= ago(2h) 
| summarize max(responseLength_s), max(requestLength_s), max(requestCharge_s), count = count() by OperationName, requestResourceType_s, userAgent_s, collectionRid_s, bin(TimeGenerated, 1h)

Get all queries that are consuming more than 100 RU/s

Find queries that consume more RU/s than a baseline amount.

This query joins with data from DataPlaneRequests and QueryRunTimeStatistics.

AzureDiagnostics
| where ResourceProvider=="MICROSOFT.DOCUMENTDB" and Category=="DataPlaneRequests" and todouble(requestCharge_s) > 100.0
| project activityId_g, requestCharge_s
| join kind= inner (
        AzureDiagnostics
        | where ResourceProvider =="MICROSOFT.DOCUMENTDB" and Category == "QueryRuntimeStatistics"
        | project activityId_g, querytext_s
) on $left.activityId_g == $right.activityId_g
| order by requestCharge_s desc
| limit 100

Get the request charges and the execution duration of a query

Get statistics in both request charge and duration for a specific query.

AzureDiagnostics
| where TimeGenerated >= ago(24hr)
| where Category == "QueryRuntimeStatistics"
| join (
AzureDiagnostics
| where TimeGenerated >= ago(24hr)
| where Category == "DataPlaneRequests"
) on $left.activityId_g == $right.activityId_g
| project databasename_s, collectionname_s, OperationName1 , querytext_s,requestCharge_s1, duration_s1, bin(TimeGenerated, 1min)

Get the distribution for different operations

Group operations by the resource distribution.

AzureDiagnostics
| where ResourceProvider=="MICROSOFT.DOCUMENTDB" and Category=="DataPlaneRequests"
| where TimeGenerated >= ago(2h) 
| summarize count = count()  by OperationName, requestResourceType_s, bin(TimeGenerated, 1h)

Get the maximum throughput that a partition has consumed

Get the maximum throughput for a physical partition.

AzureDiagnostics
| where ResourceProvider=="MICROSOFT.DOCUMENTDB" and Category=="DataPlaneRequests"
| where TimeGenerated >= ago(2h) 
| summarize max(requestCharge_s) by bin(TimeGenerated, 1h), partitionId_g

Get information about the partition keys RU/s consumption per second

Measure RU/s consumption on a per-second basis per partition key.

AzureDiagnostics 
| where ResourceProvider == "MICROSOFT.DOCUMENTDB" and Category == "PartitionKeyRUConsumption" 
| summarize total = sum(todouble(requestCharge_s)) by databaseName_s, collectionName_s, partitionKey_s, TimeGenerated 
| order by TimeGenerated asc

Get request charge for a specific partition key

Measure request charge per partition key.

AzureDiagnostics 
| where ResourceProvider == "MICROSOFT.DOCUMENTDB" and Category == "PartitionKeyRUConsumption" 
| where parse_json(partitionKey_s)[0] == "2"

Get top partition keys with most RU/s consumed in a specific period

Sort partition keys based on request unit consumption within a time window.

AzureDiagnostics 
| where ResourceProvider == "MICROSOFT.DOCUMENTDB" and Category == "PartitionKeyRUConsumption" 
| where TimeGenerated >= datetime("11/26/2019, 11:20:00.000 PM") and TimeGenerated <= datetime("11/26/2019, 11:30:00.000 PM") 
| summarize total = sum(todouble(requestCharge_s)) by databaseName_s, collectionName_s, partitionKey_s 
| order by total desc

Get logs for the partition keys whose storage size is greater than 8 GB

Find logs for partition keys filtered by the size of storage per partition key.

AzureDiagnostics
| where ResourceProvider=="MICROSOFT.DOCUMENTDB" and Category=="PartitionKeyStatistics"
| where todouble(sizeKb_d) > 800000

Get P99 or P50 latencies for operations, request charge, or the length of the response

Measure performance for; operation latency, RU/s usage, and response length.

AzureDiagnostics
| where ResourceProvider=="MICROSOFT.DOCUMENTDB" and Category=="DataPlaneRequests"
| where TimeGenerated >= ago(2d)
| summarize percentile(todouble(responseLength_s), 50), percentile(todouble(responseLength_s), 99), max(responseLength_s), percentile(todouble(requestCharge_s), 50), percentile(todouble(requestCharge_s), 99), max(requestCharge_s), percentile(todouble(duration_s), 50), percentile(todouble(duration_s), 99), max(duration_s), count() by OperationName, requestResourceType_s, userAgent_s, collectionRid_s, bin(TimeGenerated, 1h)

Get control plane logs

Get control plane long using ControlPlaneRequests.

Tip

Remember to switch on the flag described in Disable key-based metadata write access, and execute the operations by using Azure PowerShell, the Azure CLI, or Azure Resource Manager.

AzureDiagnostics 
| where Category =="ControlPlaneRequests"
| summarize by OperationName

Next steps