Add database context propagation via SET CONTEXT_INFO for SQL Server

.chloggen/sql-server-context-info-propagation.yaml

@@ -0,0 +1,22 @@
+# Use this changelog template to create an entry for release notes.
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+# your pull request title with [chore] or use the "Skip Changelog" label.
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+change_type: enhancement
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+# A brief description of the change. Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add database context propagation via `SET CONTEXT_INFO` for SQL Server
+
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+issues: [2162]
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+subtext:

docs/database/sql-server.md

@@ -9,6 +9,8 @@ linkTitle: SQL Server
 <!-- toc -->
 
 - [Spans](#spans)
+- [Context propagation](#context-propagation)
+  - [SET CONTEXT_INFO](#set-context_info)
 - [Metrics](#metrics)
 
 <!-- tocstop -->
@@ -152,6 +154,39 @@ and SHOULD be provided **at span creation time** (if provided at all):
 <!-- END AUTOGENERATED TEXT -->
 <!-- endsemconv -->
 
+## Context propagation
+
+**Status**: [Development][DocumentStatus]
+
+### SET CONTEXT_INFO
+
+Instrumentations MAY propagate context using [SET CONTEXT_INFO](https://learn.microsoft.com/sql/t-sql/statements/set-context-info-transact-sql) by injecting fixed-length part of span context (trace-id, span-id, trace-flags, protocol version) before executing a query. For example, when using W3C Trace Context, only a string representation of [`traceparent`](https://www.w3.org/TR/trace-context/#traceparent-header) SHOULD be injected. Context injection SHOULD NOT be enabled by default, but instrumentation MAY allow users to opt into it.
+
+Variable context parts (`tracestate`, `baggage`) SHOULD NOT be injected since `CONTEXT_INFO` value length is limited to 128 bytes.
+
+Instrumentations that propagate context MUST execute `SET CONTEXT_INFO` on the same physical connection as the SQL statement (or reuse its transaction).
+
+Note that `SET CONTEXT_INFO` requires binary input according to its syntax: `SET CONTEXT_INFO { binary_str | @binary_var }` and has a maximum size of 128 bytes.
+
+Example:
+
+For a query `SELECT * FROM songs` where `traceparent` is `00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01`:
+
+Run the following command on the same physical connection as the SQL statement:
+
+```sql
+-- The binary conversion may be done by the application or the driver.
+DECLARE @traceparent varbinary(55);
+SET @traceparent = CAST('00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01' AS varbinary(55));
+SET CONTEXT_INFO @traceparent; 
+```
+
+Then run the query:
+
+```sql
+SELECT * FROM songs;
+```
+
 ## Metrics
 
 Microsoft SQL Server client instrumentations SHOULD collect metrics according to the general