Stores resource logs for Azure services that use Azure Diagnostics mode. Resource logs describe the internal operation of Azure resources.

The resource log for each Azure service has a unique set of columns. The AzureDiagnostics table includes the most common columns used by Azure services. If a resource log includes a column that doesn't already exist in the AzureDiagnostics table, that column is added the first time that data is collected. If the maximum number of 500 columns is reached, data for any additional columns is added to a dynamic column.

Azure services that use resource-specific mode store data in a table specific to that service and do not use the AzureDiagnostics table. See Resource Types below for the services that use each method. See Azure resource logs for details on the differences.

AdditionalFields column

Unlike other tables, AzureDiagnostics is much more susceptible to exceeding the 500 column limit imposed for any table in a Log Analytics workspace due to the wide assortment of Azure Resources capable of sending data to this table. To ensure that no data is lost due to the number of active columns exceeding this 500 column limit, AzureDiagnostics column creation is handled in a different manner to other tables.

The AzureDiagnostics table in every workspace will contain at a minimum the same 200 columns. For workspaces created before January 19, 2021, the table will also contain any columns that were already in place prior to this date. When data is sent to a column not already in place:

  • If the total number of columns in AzureDiagnostics in the current workspace does not exceed 500, a new column will be created just like with any other table.
  • If the total number of columns is at or above 500, the excess data is added to a dynamic property bag column called AdditionalFields as a property.


To illustrate this behavior, imagine that as of (deployment date) the AzureDiagnostics table in our workpsace looks as follows:

Column 1 Column 2 Column 3 ... Column 498
abc def 123 ... 456
... ... ... ... ...

A resource that sends data to AzureDiagnostics then adds a new dimension to their data that they call NewInfo1. Since the table still has less than 500 columns, the first time an event occurs that contains data for this new dimension will add a new column to the table:

Column 1 Column 2 Column 3 ... Column 498 NewInfo1_s
abc def 123 ... 456 xyz
... ... ... ... ... ...

You can return this new data in a simple query:

AzureDiagnostics | where NewInfo1_s == "xyz"

At a later date, another resource sends data to AzureDiagnostics that adds new dimensions called NewInfo2 and NewInfo3. Because the table has reached 500 columns in this workspace, the new data will go into the AdditionalFields column:

Column 1 Column 2 Column 3 ... Column 498 NewInfo1_s AdditionalFields
abc def 123 ... 456 xyz {"NewInfo2":"789","NewInfo3":"qwerty"}
... ... ... ... ... ... ...

You can still query for this data,but you must extract it from the property bag using any of the dynamic property operators in KQL:

| where AdditionalFields.NewInfo2 == "789" and AdditionalFields.NewInfo3 == "qwerty"

Tips on using AdditionalFields column

While general query best practices such as always filtering by time as the first clause in the query should be followed, there are some other recommendations you should consider when working with AdditionalFields:

  • You will need to typecast data prior to performing further operations on it. For example, if a column exists called Perf1Sec_i as well as a property in AdditionalFields called Perf2Sec, and you want to calculate total perf by adding both values, use something like: AzureDiagnostics | extend TotalPerfSec = Perf1Sec_i + toint(AdditionalFields.Perf2Sec) | .....
  • Use where clauses to reduce the data volume to the smallest possible prior to writing any complex logic to significantly improve performance. TimeGenerated is one column that should always be reduced to the smallest possible window. In the case of AzureDiagnostics, an additional filter should also always be included at the top of the query around the resource types that are being queried using the ResourceType column.
  • When querying very large volumes of data, it is sometimes more efficient to do a filter on AdditionalFields as a whole rather than parsing it. For example, for large volumes of data AzureDiagnostics | where AdditionalFields has "Perf2Sec" is often more efficient than AzureDiagnostics | where isnotnull(toint(AdditionalFields.Perf2Sec)).

Azure Diagnostics mode

The following services use Azure diagnostics mode for their resource logs and send data to the Azure Diagnostics table.

  • Analysis Services
  • Application Gateways
  • Automation Accounts
  • Azure Database for MariaDB servers
  • Azure Database for MySQL servers
  • Azure Database for PostgreSQL servers
  • Azure Database for PostgreSQL servers v2
  • Batch accounts
  • CDN profiles
  • Cognitive Services
  • Data Lake Analytics
  • DataLake Storage Gen1
  • Device Provisioning Services
  • Digital Twins
  • Event Grid Topics
  • Event Hubs
  • ExpressRoute circuits
  • Front Doors
  • Integration accounts
  • Key Vault
  • Kubernetes services
  • Load balancers
  • Logic Apps
  • Media services
  • Network interfaces
  • Network Security Groups
  • P2S VPN Gateways
  • Power BI Embedded
  • Public IP addresses
  • Recovery Services vaults(Site Recovery)
  • Search services
  • Service Bus
  • SQL databases
  • SQL managed Instances
  • SQL servers
  • Stream Analytics jobs
  • Traffic Manager profiles
  • Virtual networks
  • Virtual network gateways
  • VPN Gateways

Azure Diagnostics mode or resource-specific mode

The following services use either Azure diagnostics mode or resource-specific mode for their resource logs depending on their configuration. When they use resource-specific mode, they do not send data to the AzureDiagnostics table. See Azure resource logs for details on this configuration.

  • API Management Services
  • Azure Cosmos DB
  • Data factories (V2)
  • IoT Hub
  • Recovery Services vaults(Backup)
  • Firewalls


  • Azure Resources
  • Security
  • Network


  • LogManagement

Resource types

  • Application Gateways
  • CDN Profiles
  • Azure Cosmos DB
  • Event Grid Topics
  • Event Hubs
  • Firewalls
  • Key Vaults
  • Kubernetes Services
  • Recovery Services Vaults
  • Service Bus
  • Azure Database for MySQL Flexible Servers
  • Azure Database for PostgreSQL Flexible Servers
  • Media Services
  • Analysis Services
  • Batch Accounts
  • Cognitive Services
  • Event Grid Partner Namespaces
  • Event Grid Partner Topics
  • Event Grid System Topics
  • Azure Arc Enabled Kubernetes
  • Azure Arc Provisioned Clusters
  • IoT Hub
  • Logic Apps
  • API Management services
  • Automation account
  • Data factories
  • Data Lake Storage Gen1
  • Data Lake Analytics
  • Power BI Embedded
  • SQL Managed Instances
  • SQL Servers
  • SQL Databases
  • Azure Database for MySQL Servers
  • Azure Database for PostgreSQL Servers
  • Azure Database for PostgreSQL Servers V2
  • Azure Database for MariaDB Servers
  • Device Provisioning Services
  • ExpressRoute Circuits
  • Front Doors
  • Network Interfaces
  • Network Security Groups
  • Public IP Addresses
  • Traffic Manager Profiles
  • Virtual Network Gateways
  • Virtual Private Network Gateways
  • Virtual Networks
  • Search Services
  • Stream Analytics jobs


Column Type Description
action_id_s String
action_name_s String
action_s String
ActivityId_g Guid
AdHocOrScheduledJob_s String
application_name_s String
audit_schema_version_d Double
avg_cpu_percent_s String
avg_mean_time_s String
backendHostname_s String
Caller_s String
callerId_s String
CallerIPAddress String
calls_s String
Category String
client_ip_s String
clientInfo_s String
clientIP_s String
clientIp_s String
clientIpAddress_s String
clientPort_d Double
code_s String
collectionName_s String
conditions_destinationIP_s String
conditions_destinationPortRange_s String
conditions_None_s String
conditions_protocols_s String
conditions_sourceIP_s String
conditions_sourcePortRange_s String
CorrelationId String
count_executions_d Double
cpu_time_d Double
database_name_s String
database_principal_name_s String
DatabaseName_s String
db_id_s String
direction_s String
dop_d Double
duration_d Double
duration_milliseconds_d Double
DurationMs BigInt
ElasticPoolName_s String
endTime_t DateTime
Environment_s String
error_code_s String
error_message_s String
errorLevel_s String
event_class_s String
event_s String
event_subclass_s String
event_time_t DateTime
EventName_s String
execution_type_d Double
executionInfo_endTime_t DateTime
executionInfo_exitCode_d Double
executionInfo_startTime_t DateTime
host_s String
httpMethod_s String
httpStatus_d Double
httpStatusCode_d Double
httpStatusCode_s String
httpVersion_s String
id_s String
identity_claim_appid_g Guid
identity_claim_ipaddr_s String
instanceId_s String
interval_end_time_d Double
interval_start_time_d Double
ip_s String
is_column_permission_s String
isAccessPolicyMatch_b Bool
JobDurationInSecs_s String
JobFailureCode_s String
JobId_g Guid
jobId_s String
JobOperation_s String
JobOperationSubType_s String
JobStartDateTime_s String
JobStatus_s String
JobUniqueId_g Guid
Level String
log_bytes_used_d Double
logical_io_reads_d Double
logical_io_writes_d Double
LogicalServerName_s String
macAddress_s String
matchedConnections_d Double
max_cpu_time_d Double
max_dop_d Double
max_duration_d Double
max_log_bytes_used_d Double
max_logical_io_reads_d Double
max_logical_io_writes_d Double
max_num_physical_io_reads_d Double
max_physical_io_reads_d Double
max_query_max_used_memory_d Double
max_rowcount_d Double
max_time_s String
mean_time_s String
Message String
min_time_s String
msg_s String
num_physical_io_reads_d Double
object_id_d Double
object_name_s String
OperationName String
OperationVersion String
partitionKey_s String
physical_io_reads_d Double
plan_id_d Double
policy_s String
policyMode_s String
primaryIPv4Address_s String
priority_d Double
properties_enabledForDeployment_b Bool
properties_enabledForDiskEncryption_b Bool
properties_enabledForTemplateDeployment_b Bool
properties_s String
properties_sku_Family_s String
properties_sku_Name_s String
properties_tenantId_g Guid
query_hash_s String
query_id_d Double
query_max_used_memory_d Double
query_plan_hash_s String
query_time_d Double
querytext_s String
receivedBytes_d Double
Region_s String
requestCharge_s String
requestQuery_s String
requestResourceId_s String
requestResourceType_s String
requestUri_s String
reserved_storage_mb_s String
Resource String
resource_actionName_s String
resource_location_s String
resource_originRunId_s String
resource_resourceGroupName_s String
resource_runId_s String
resource_subscriptionId_g Guid
resource_triggerName_s String
resource_workflowId_g Guid
resource_workflowName_s String
ResourceGroup String
_ResourceId String A unique identifier for the resource that the record is associated with
ResourceProvider String
ResourceProvider String
ResourceType String
ResourceType String
response_rows_d Double
resultCode_s String
ResultDescription String
ResultDescription String
resultDescription_ChildJobs_s String
resultDescription_ErrorJobs_s String
resultMessage_s String
ResultSignature String
ResultType String
ResultType String
rootCauseAnalysis_s String
routingRuleName_s String
rowcount_d Double
ruleName_s String
RunbookName_s String
RunOn_s String
schema_name_s String
sentBytes_d Double
sequence_group_id_g Guid
sequence_number_d Double
server_principal_sid_s String
session_id_d Double