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SQL Server 2017 - 2022Memory & Resource Governor

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Msg 8645, Level 17: A timeout occurred while waiting for memory resources to execute the query in resource pool 'default'

SQL Server Query Memory Grant Timeout: Excessive Sort/Hash Workspace Grants & Resource Governor Isolation

Diagnosing queries consuming oversized workspace grants due to cardinality misestimations, analyzing sys.dm_exec_query_memory_grants, and tuning buffer limits.

Reviewed by:Senior Database Architect & SRE (dataiotech Labs)

Tested Versions: SQL Server 2017 / 2019 / 2022

Operational Verification & Reliability Metadata

Last Technical Review: 2 Kasım 2026

Tested VersionsSQL Server 2019 CU27, 2022 CU14

Required PrivilegesVIEW SERVER STATE privilege

Risk Assessment

HighDBCC FREEPROCCACHE purges compiled plan cache causing immediate CPU recompilation spikes

Expected Outputsys.dm_exec_query_memory_grants showing zero pending requests with grant_time IS NULL

Rollback Procedure:Re-align max server memory and Resource Governor limits

Microsoft Docs: sys.dm_exec_query_memory_grants

First 60 Seconds Emergency Protocol:

The error string is a symptom, not the root cause. Do not restart the server blindly. Run the diagnostic queries below to pinpoint the actual failure mode.

▸Symptom

Queries abort under memory semaphore throttling:

plaintext

Msg 8645, Level 17, State 1, Line 1
A timeout occurred while waiting for memory resources to execute the query in resource pool 'default' (8192).

▸What You See in Production

RESOURCE_SEMAPHORE wait types skyrocket. Concurrent queries queue endlessly waiting for memory workspace grants.

▸Root Cause Matrix

Probability	Root Cause	Description
%60	Cardinality Misestimation	Stale statistics trick optimizer into requesting massive gigabyte workspace grants.
%25	Unindexed Hash/Sort Operations	Heavy joins executing in-memory rather than streaming indexed rows.
%15	Suboptimal `max server memory`	Buffer pool capped too tightly for concurrent analytical load.

▸EMERGENCY RUNBOOK (0-5 min)

sql

-- 1. Locate sessions waiting for memory grants
SELECT session_id, requested_memory_kb, granted_memory_kb 
FROM sys.dm_exec_query_memory_grants 
WHERE grant_time IS NULL;

-- 2. Kill the blocking query
KILL 78;

-- 3. Emergency plan cache purge
DBCC FREEPROCCACHE;

▸PERMANENT BLUEPRINT

1Statistics Maintenance: Run regular automated maintenance with full sampling.
2Resource Governor Workload Pools: Confine analytical queries to dedicated memory pools.

▸Verification

sql

SELECT waiter_count, total_memory_kb, available_memory_kb 
FROM sys.dm_exec_query_resource_semaphores;

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