How to fix Error 10646 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 10646 – Index Cannot Be Dropped Using DROPEXISTING on SNAPSHOTMATERIALIZATION View

Why This Error Happens

This error occurs because SQL Server 2025 prohibits using the DROP_EXISTING clause to rebuild an index on an indexed view that has SNAPSHOT_MATERIALIZATION enabled. The restriction exists because dropping and recreating the clustered index in a single atomic operation could invalidate the snapshot’s internal consistency metadata, which SQL Server relies on to serve temporally consistent reads. Essentially, the engine blocks this shortcut to prevent corruption of the materialized snapshot state, forcing an explicit drop-then-create sequence instead.

Step-by-Step Resolution Guide

Step 1: Identify the Affected Index and View

  • Run the following query to confirm the index and view names from the error message:
  • SELECT i.name AS IndexName, v.name AS ViewName FROM sys.indexes i JOIN sys.views v ON i.object_id = v.object_id WHERE v.name = 'YourViewName';
  • Confirm SNAPSHOT_MATERIALIZATION is active by checking sys.views or the view’s definition with sp_helptext.

Step 2: Explicitly Drop the Existing Index

  • Instead of using CREATE INDEX ... WITH (DROP_EXISTING = ON), issue a standalone DROP INDEX statement first.
  • Example: DROP INDEX [IX_YourIndexName] ON [dbo].[YourViewName];
  • Verify the index no longer appears in sys.indexes for that object.

Step 3: Recreate the Index Without DROP_EXISTING

  • Create the new (or modified) index as a separate statement, omitting the DROP_EXISTING option entirely.
  • Example: CREATE UNIQUE CLUSTERED INDEX [IX_YourIndexName] ON [dbo].[YourViewName] (ColumnA, ColumnB);
  • Ensure SET ARITHABORT ON, SET NUMERIC_ROUNDABORT OFF, and other required session settings for indexed views are configured before running this step.

Step 4: Script and Automate Future Maintenance

  • Update any deployment scripts, DACPAC definitions, or SSDT projects that previously used DROP_EXISTING = ON for this view’s index.
  • Replace them with the two-step drop/create pattern to prevent recurrence during future deployments or index maintenance jobs.

Alternative or Verification Steps

  • Verify the fix by querying sys.indexes and sys.dm_db_index_physical_stats to confirm the index exists, is healthy, and matches the expected definition.
  • If the view no longer requires snapshot consistency, consider disabling SNAPSHOT_MATERIALIZATION on the view (via ALTER VIEW) before performing index maintenance, then re-enable it afterward if needed.