How to fix Error 6398 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 6398 – Selective XML Index MAXLENGTH Out of Range

Why This Error Happens

This error occurs when creating or altering a Selective XML Index (SXI) and the MAXLENGTH option specified for a given XML path exceeds the permissible boundary enforced by SQL Server’s internal path-promotion engine. SQL Server 2025 validates the MAXLENGTH value against the data type used to store the promoted node (for example, nvarchar or varbinary), and any value outside the allowed byte range triggers a hard validation failure before the index is built. This is typically caused by a copy-pasted T-SQL script with a value from a different schema, a manual typo, or an attempt to set MAXLENGTH larger than the maximum supported row/column size for the chosen data type.

Step-by-Step Resolution Guide

Step 1: Identify the Offending Path and Current Value

  • Open the exact CREATE SELECTIVE XML INDEX or CREATE XML INDEX ... USING XML INDEX statement that triggered Error 6398.
  • Locate the specific XML path referenced in the error message (the %.*ls placeholder will show the actual path, e.g., /Root/Customer/@id).
  • Note the current MAXLENGTH value assigned to that path in your WITH (PATHS (...)) clause.

Step 2: Check the Allowed Range in the Error Output

  • Re-run the failing script in SQL Server Management Studio (SSMS) and capture the full error text, which includes the two bounding numbers (%d - %d).
  • For most promoted scalar types in SQL Server 2025, the valid range is typically 1 through 4000 for nvarchar-based promotions, or up to 8000 for varbinary/varchar based types — confirm using the exact numbers from your error message since this can vary by data type.
  • Cross-reference the path’s declared SQL_TYPE in your index definition (e.g., AS SQL nvarchar(100)) since MAXLENGTH must stay within that type’s storage ceiling.

Step 3: Correct the MAXLENGTH Value in the Index Definition

  • Edit the T-SQL script and adjust the MAXLENGTH parameter to fall within the reported valid range.
  • Example fix:
CREATE SELECTIVE XML INDEX SXI_Orders
ON dbo.OrdersTable (XmlColumn)
FOR XML INDEX PXML_Orders
PATHS
(
    '/Root/Customer/@id' AS SQL nvarchar(100) MAXLENGTH 100
)
  • Ensure the MAXLENGTH value matches or is smaller than the declared SQL nvarchar(n) / varbinary(n) length to avoid truncation conflicts.

Step 4: Drop and Recreate the Index

  • If the Selective XML Index partially exists from a failed creation attempt, drop it first:
DROP XML INDEX IF EXISTS SXI_Orders ON dbo.OrdersTable;
  • Re-execute the corrected CREATE SELECTIVE XML INDEX statement.

Step 5: Validate Server and Database Compatibility Level

  • Confirm the database is running at a compatibility level that supports Selective XML Indexes (130 or higher) using:
SELECT compatibility_level FROM sys.databases WHERE name = 'YourDatabaseName';
  • If the compatibility level is outdated, update it with ALTER DATABASE YourDatabaseName SET COMPATIBILITY_LEVEL = 160; (adjust to your SQL Server 2025 supported level) and retry the index creation.

Alternative or Verification Steps

  • Verify the fix by querying sys.selective_xml_index_paths to confirm the path was registered successfully with the corrected max_length value: SELECT * FROM sys.selective_xml_index_paths WHERE path_id = (SELECT object_id FROM sys.indexes WHERE name = 'SXI_Orders');
  • If the error persists despite correct values, rebuild the underlying XML schema collection (if one is bound to the column) and retry, as a stale or corrupted XML Schema Collection can sometimes cause SQL Server to miscalculate allowed length boundaries.