All available query memory is consumed by other concurrent queries. A single large query requests more memory than the server can grant. SQL Server max server memory is set too low relative to query memory needs

Step 1: Find queries waiting for memory grants: SELECT * FROM sys.dm_exec_query_memory_grants WHERE granted_memory_kb IS NULL;. Step 2: Identify the top memory consumers: SELECT TOP 10 session_id, requested_memory_kb, granted_memory_kb FROM sys.dm_exec_query_memory_grants ORDER BY requested_memory_kb DESC;. Step 3: Add indexes to eliminate the sort/hash operations causing the large memory grant, or increase max server memory: EXEC sp_configure 'max server memory (MB)', 16000; RECONFIGURE;

High severityresource

Power BI Refresh Error:
8645

What does this error mean?

A query waited too long for a memory grant to execute a sort or hash operation — the grant was never available.

Common causes

1All available query memory is consumed by other concurrent queries
2A single large query requests more memory than the server can grant
3SQL Server max server memory is set too low relative to query memory needs

How to fix it

1Step 1: Find queries waiting for memory grants: SELECT * FROM sys.dm_exec_query_memory_grants WHERE granted_memory_kb IS NULL;
2Step 2: Identify the top memory consumers: SELECT TOP 10 session_id, requested_memory_kb, granted_memory_kb FROM sys.dm_exec_query_memory_grants ORDER BY requested_memory_kb DESC;
3Step 3: Add indexes to eliminate the sort/hash operations causing the large memory grant, or increase max server memory: EXEC sp_configure 'max server memory (MB)', 16000; RECONFIGURE;

Frequently asked questions

How do I reduce the memory grant required by a query?

The primary way is adding indexes that eliminate sorts and hash operations — these are the main consumers of memory grants. Run the query in SSMS with Actual Execution Plan and look for Sort and Hash Match operators.

What is QUERY_GOVERNOR and can it prevent 8645?

QUERY_GOVERNOR limits query cost, not memory — it does not prevent 8645. Use Resource Governor to limit memory grants per workload group: ALTER RESOURCE POOL with MAX_MEMORY_PERCENT.

Can error 8645 be avoided by using a smaller batch size in ADF?

Yes — reducing the batch size in ADF copy activities reduces the size of sort and hash operations, which reduces the required memory grant. Try batch sizes of 10,000–50,000 rows.

Official documentation: https://learn.microsoft.com/en-us/sql/relational-databases/errors-events/mssqlserver-8645-database-engine-error