Workaround for querying deadlocks in extended events

[nenadnoveljic]

What does this PR do?

Implements the workaround for querying deadlocks in extended events (XE) views.

Motivation

SQL Server limitation: Querying the extended events ring buffer may not show the latest events.

Additional Notes

The ring buffer in sys.dm_xe_session_targets.target_data is externalized as one large XML, limited to 4MB, even though it's NVARCHAR(MAX). If the XML exceeds 4MB, the latest events are not shown.

To avoid this, we're creating a dedicated datadog XE session with a 1MB buffer, which prevents XML overflow. Since the XML typically uses half the allocated buffer space, a 1MB buffer gives us an 8x safety margin.

select t.name,  t.xml_size / r.value('@memoryUsed', 'float') xml_size_to_buffer_size_ratio from 
(SELECT  
  s.name, len(t.target_data) xml_size, cast(t.target_data as xml) as target_data_xml
FROM    sys.dm_xe_sessions s
JOIN 
    sys.dm_xe_session_targets t ON s.address = t.event_session_address
WHERE t.target_name = 'ring_buffer' and name in ('system_health', 'datadog')) as t
    CROSS APPLY target_data_xml.nodes('RingBufferTarget') AS x(r)

name	xml_size_to_buffer_size_ratio
system_health	1,081729263927248
datadog	0,5115150146759991

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[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 14 lines in your changes missing coverage. Please review.

Project coverage is 88.27%. Comparing base (50589cb) to head (cefeb94).
Report is 1 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
activemq	?
cassandra	?
hive	?
hivemq	?
ignite	?
jboss_wildfly	?
kafka	?
presto	?
solr	?
sqlserver	89.23% <66.66%> (+9.48%)	⬆️

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[github-actions]

The changelog type changed or removed was used in this Pull Request, so the next release will bump major version. Please make sure this is a breaking change, or use the fixed or added type instead.

[github-actions]

The changelog type changed or removed was used in this Pull Request, so the next release will bump major version. Please make sure this is a breaking change, or use the fixed or added type instead.

[github-actions]

The changelog type changed or removed was used in this Pull Request, so the next release will bump major version. Please make sure this is a breaking change, or use the fixed or added type instead.

[lu-zhengda]

I suggest to create a custom exception class NoXeSessionException(Exception) so that we can catch the specific exception when needed

[lu-zhengda]

btw i also don't see error handling of in _set_xe_session_name and _query_deadlocks. if an exception is raised here, it will fail the thread. should we catch the exception and log an error message?

[nenadnoveljic]

The custom exception NoXeSessionException is now raised in _set_xe_session_name and caught in _query_deadlocks.

[github-actions]

The changelog type changed or removed was used in this Pull Request, so the next release will bump major version. Please make sure this is a breaking change, or use the fixed or added type instead.

[github-actions]

The changelog type changed or removed was used in this Pull Request, so the next release will bump major version. Please make sure this is a breaking change, or use the fixed or added type instead.

[github-actions]

The changelog type changed or removed was used in this Pull Request, so the next release will bump major version. Please make sure this is a breaking change, or use the fixed or added type instead.

[github-actions]

The changelog type changed or removed was used in this Pull Request, so the next release will bump major version. Please make sure this is a breaking change, or use the fixed or added type instead.