Fabric gotchas

Common gotchas & troubleshooting

Issue	Cause	Fix
401 Unauthorized	Wrong token audience	Check audience table in fabric-auth skill; verify aud claim at jwt.ms
403 Forbidden on Power BI API	User has Viewer role	Refresh/data sources/permissions APIs require Contributor+. Stop retrying — it's permissions.
404 EntityNotFound on getDefinition	Insufficient permissions masquerading as 404	Check workspace role first; don't retry with different URLs
PowerBIEntityNotFound / EntityNotFound from pipeline, Variable Library, or REST call	Used .platform logicalId instead of runtime item ID	Fetch runtime ID from Fabric portal URL or GET /v1/workspaces/{wsId}/items. See fabric-rest-api skill (Item IDs section)
Login failed... database not found	Wrong Initial Catalog	Use item display name, not FQDN. Verify workspace role. Connections with no Initial Catalog now land deterministically on master (drill-verified) — confirm with SELECT DB_NAME() and switch with USE [<item display name>] instead of reconnecting.
Error 24556/24706 snapshot conflict	Concurrent writes to same table	Serialize writes; retry with backoff
nvarchar / datetime / money errors	Unsupported types in Fabric Warehouse	Use varchar, datetime2(6), decimal(19,4) (Warehouse only — fabric-database skill supports these)
COPY INTO auth error	Missing Storage Blob Data Reader on ADLS	Grant role or use SAS in CREDENTIAL
MERGE failures in production	Preview feature with table-level conflict detection	Use DELETE + INSERT pattern instead (Warehouse only — fabric-database skill supports MERGE)
ALTER COLUMN fails	Not supported in Fabric Warehouse	Use CTAS + sp_rename workaround (Warehouse only — fabric-database skill supports ALTER COLUMN)
TMDL validation error	Spaces instead of tabs, or // comments	Use literal tabs; use /// for descriptions
Parts missing after updateDefinition	Only modified parts sent	Must include ALL parts in every update
DefaultJob in job execution	Wrong jobType	Use type-specific values: RunNotebook, Pipeline, SparkJob, Refresh
sqlcmd not found or ODBC errors	Wrong sqlcmd version	Use Go version: winget install sqlcmd (not ODBC /opt/mssql-tools/ version)
Slow / stale Lakehouse SQLEP queries	Small-file problem, or metadata-sync lag on newly-landed data	Run OPTIMIZE and VACUUM via Spark. If on the new metadata-sync preview, diagnose staleness via the DMV / targeted refresh in the note below
Query Insights empty	Views not yet generated after creation	Wait ~2 minutes
OneLake 401	Wrong storage audience	Must use https://storage.azure.com/.default exactly
TDS connection timeout	Port 1433 blocked	Open outbound TCP 1433; allow *.datawarehouse.fabric.microsoft.com
Cross-database query fails	Items in different regions or workspaces	All items must share same workspace AND region
Notebook upload 400 exceptionCulprit:1	Cell source is a bare string, not an array	Convert every cell's source to array-of-strings form (["line\n", "line\n", "last"]). Applies to markdown and code cells.
CloudEventPropertyMissingException: ...type is missing when publishing to a schema-associated Eventstream custom endpoint	Attributes sent in the JSON body / structured mode	Send binary-mode CloudEvents: cloudEvents:-prefixed Event Hub application properties (not body). See [[fabric-eventstream]] — Producing to a schema-associated custom endpoint

Slow SQLEP — new metadata sync (preview, May 2026): on endpoints created with the new opt-in metadata sync, target a single table with EXEC sys.sp_dw_refresh_ext_table '<schema.table>' and inspect last sync time / blocked state via sys.dm_db_external_tables_log_status. Full preview note (scope, enablement, limitations): [[fabric-spark]].

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Best Practices Summary

MUST

• Verify workspace has capacity before creating items (capacityId in workspace response)
• Use parameterized notebooks and pipelines — no hardcoded workspace/item IDs
• Use Delta Lake format for all Lakehouse tables
• Include time filters in KQL queries
• Label queries with OPTION (LABEL = ...) for tracking
• Always specify database name in SQL connections (-d flag or Initial Catalog)
• Use Entra ID auth everywhere — SQL auth not supported in Fabric

PREFER

• Medallion architecture (Bronze/Silver/Gold) for data organization
• REST APIs for programmatic management over portal clicks
• Incremental processing over full refreshes
• CTAS over CREATE TABLE + INSERT for large transforms
• COPY INTO for external file ingestion
• DELETE + INSERT over MERGE for production upserts
• Distributed #temp tables (ROUND_ROBIN) over non-distributed
• EXISTS over IN for large subqueries
• UNION ALL over UNION when duplicates are acceptable
• Integer keys over string keys for relationships

AVOID

• Hardcoded workspace/item IDs — discover via REST API
• Confusing .platform logicalId with runtime item ID — they are NOT interchangeable; runtime references need the portal/API ID
• SELECT * without LIMIT on large tables
• Long-running transactions (increases conflict window)
• Singleton INSERT...VALUES at scale (creates tiny Parquet files)
• DROP TABLE IF EXISTS + CREATE TABLE to refresh (loses time-travel history) — use TRUNCATE + INSERT
• IFERROR in DAX (performance degradation)
• FOR XML (use FOR JSON instead)
• Manual lineageTag or PBI_* annotations in TMDL
• Unbounded streaming queries
• MARS in connection strings

Reference

• Microsoft Learn: Troubleshoot the Warehouse (canonical error/cause/fix)
• Microsoft Learn: T-SQL surface area in Fabric Data Warehouse (unsupported commands)
• Microsoft Learn: Transactions in Fabric Data Warehouse (24556/24706 write-write conflicts)
• Comprehensive MS Learn link bundle (per-error-class deep-dive index — auth/IDs/TDS/snapshot/T-SQL/COPY/REST/Lakehouse SQLEP/notebook/throttling/OneLake): references/REFERENCE.md

See also

• fabric-auth skill — token audience table (for 401 diagnosis)
• fabric-rest-api skill — logicalId vs runtime ID detail
• fabric-warehouse skill — Warehouse-specific type and feature restrictions
• fabric-database skill — what's different when it's SQL Database (most restrictions don't apply)
• fabric-spark skill — notebook upload array-of-strings requirement