SQL panel freezes or crashes with large IN clauses

[kkm-horikawa]

Description

When SQL queries contain large IN clauses with thousands of parameters (e.g., UUIDs), the SQL panel either:

• Freezes for 10-18+ seconds (sqlparse < 0.5.5)
• Crashes with SQLParseError (sqlparse >= 0.5.5)

This is a common pattern when fetching IDs from one query and filtering by them in another:

job_ids = list(Campaign.objects.filter(...).values_list('job_id', flat=True))
# job_ids contains 5000+ UUIDs
applications = JobApplication.objects.filter(job_id__in=job_ids)

Behavior Matrix

debug-toolbar	sqlparse	When	Behavior
<= 5.x	< 0.5.5	Page load	Freezes 10-18+ seconds
<= 5.x	>= 0.5.5	Page load	SQLParseError crash
>= 6.x	< 0.5.5	SQL panel click	Freezes 10-18+ seconds
>= 6.x	>= 0.5.5	SQL panel click	SQLParseError crash

Demo

debug-toolbar 5.2 + sqlparse 0.5.3 (page freezes)

debug-toolbar 6.1 + sqlparse 0.5.5 (SQLParseError)

Reproduction

A minimal reproduction project is available:
👉 https://github.com/kkm-horikawa/debug-toolbar-perf-issue

git clone https://github.com/kkm-horikawa/debug-toolbar-perf-issue.git
cd debug-toolbar-perf-issue
uv sync
uv run python manage.py migrate
uv run python manage.py runserver
# Visit http://127.0.0.1:8000/slow/?count=5000

Current Workaround

DEBUG_TOOLBAR_CONFIG = {
    'PRETTIFY_SQL': False,  # Disables ALL SQL formatting
}

This disables formatting for all queries, not just problematic ones.

Related

• Some SQL queries make debug toolbar rendering very slow #1402
• sqlparse 0.5.5 causing Maximum number of tokens exceeded in DBT queries andialbrecht/sqlparse#828

[tim-schilling]

Let's start with a PR that gracefully handles SQLParseError.