SQL Server Error 8651

Error number

8651

Severity

17 (resource or software problem)

State

Not documented by Microsoft (not reproduced here)

Product

Microsoft SQL Server Database Engine

Versions

All supported SQL Server versions (2016 to 2025)

Category

Memory

Last reviewed

24 October 2026

What it means

Error 8651 means a query could not be given the memory grant it needs to run (for sorts, hashes and similar work) in the named resource pool, so it failed instead of starting.

Queries with memory-hungry operators get a memory grant before they start, from the grant memory of their resource pool. Error 8651 is raised when the grant the query requires cannot be provided in that pool. Microsoft's reference explains it as other processes consuming server memory, and its older message text tied it to the min memory per query setting: every grant is at least that size, so a high value makes grants harder to satisfy.

Read the pool name and pool_id: default (2) means ordinary work on an instance short of grant memory; a user-defined pool points to Resource Governor limits, which the message itself suggests checking. Severity 17 means a resource ran out; the server keeps running. If queries are queuing for grants and failing after a wait, you will see 8645 instead or as well.

Common causes

• Memory pressure on the instance: other processes or SQL Server components using memory, leaving too little for query grants.
• Concurrent queries with large grants (big sorts and hash joins) holding most of the pool's grant memory.
• A Resource Governor pool with a low MAX_MEMORY_PERCENT, or a workload group with a low REQUEST_MAX_MEMORY_GRANT_PERCENT, for the work that runs in it.
• An unusually high min memory per query setting, which raises the minimum size of every grant.
• Overestimated row counts that make queries ask for far more memory than they use.

Diagnose it

Read-only These queries only read metadata and dynamic management views. They do not change data, permissions or configuration, so they are safe to run first.

SELECT pool_id, resource_semaphore_id,
       total_memory_kb / 1024 AS total_mb, available_memory_kb / 1024 AS available_mb,
       granted_memory_kb / 1024 AS granted_mb, used_memory_kb / 1024 AS used_mb,
       grantee_count, waiter_count
FROM sys.dm_exec_query_resource_semaphores;

SELECT mg.session_id, mg.pool_id, mg.group_id,
       mg.required_memory_kb / 1024 AS required_mb, mg.requested_memory_kb / 1024 AS requested_mb,
       mg.granted_memory_kb / 1024 AS granted_mb, mg.max_used_memory_kb / 1024 AS max_used_mb,
       t.text AS query_text
FROM sys.dm_exec_query_memory_grants AS mg
OUTER APPLY sys.dm_exec_sql_text(mg.sql_handle) AS t
ORDER BY mg.granted_memory_kb DESC;

SELECT p.pool_id, p.name AS pool_name, p.max_memory_kb / 1024 AS max_mb,
       p.used_memory_kb / 1024 AS used_mb, p.out_of_memory_count, p.total_memgrant_count
FROM sys.dm_resource_governor_resource_pools AS p;

SELECT g.group_id, g.name AS group_name, g.pool_id,
       g.request_max_memory_grant_percent, g.max_request_grant_memory_kb / 1024 AS max_grant_mb
FROM sys.dm_resource_governor_workload_groups AS g;

SELECT total_physical_memory_kb / 1024 AS total_mb,
       available_physical_memory_kb / 1024 AS available_mb,
       system_memory_state_desc
FROM sys.dm_os_sys_memory;

SELECT TOP (10) type, SUM(pages_kb) / 1024 AS pages_mb
FROM sys.dm_os_memory_clerks
GROUP BY type
ORDER BY pages_mb DESC;

SELECT name, value_in_use
FROM sys.configurations
WHERE name IN (N'max server memory (MB)', N'min server memory (MB)', N'min memory per query (KB)');

How to fix it

Each fix is labelled with what it changes. Try read-only checks and the least invasive fix first, and test changes outside production.

SELECT ProductId, SUM(Quantity) AS Units
FROM dbo.OrderLines
GROUP BY ProductId
ORDER BY Units DESC
OPTION (MAX_GRANT_PERCENT = 10);

Examples

A query cannot get its memory grant under memory pressure

Shown from the engine message catalogue; not reproduced here because it needs memory pressure or a Resource Governor change on the whole instance. The level and state a client sees were not observed in the lab, so only the message text is shown; the catalogue severity is 17.

SELECT o.CustomerId, l.ProductId, SUM(l.Quantity) AS Units
FROM dbo.Orders AS o
JOIN dbo.OrderLines AS l ON l.OrderId = o.OrderId
GROUP BY o.CustomerId, l.ProductId
ORDER BY Units DESC;

Could not perform the operation because the requested memory grant was not available in resource pool 'default' (2).  Rerun the query, reduce the query load, or check resource governor configuration setting.

How to prevent it

Keep an eye on grant memory: the largest grants in the plan cache or Query Store, waiters in sys.dm_exec_query_resource_semaphores, and Memory Grants Pending. Tune new heavy queries before they reach production.

Leave memory settings such as min memory per query at their defaults unless a measured problem says otherwise, and size Resource Governor pools from the grants their workloads actually request.

Common questions

Learn more on CodeWithSQL

• Performance tuning
• SQL indexes

Official documentation

• MSSQLSERVER_8651 (Microsoft Learn)
• Troubleshoot memory grant issues
• sys.dm_exec_query_resource_semaphores
• Resource Governor

Last technically reviewed 24 October 2026; examples and diagnostics run on SQL Server 2025 (17.0.1145.4). Message text checked against the engine's sys.messages catalogue.