TOO_MANY_SIMULTANEOUS_QUERIES ClickHouse® error¶

The TOO_MANY_SIMULTANEOUS_QUERIES error in ClickHouse® (and Tinybird) happens when the system has reached its configured limit for the number of queries that can run simultaneously. This typically occurs in high-traffic scenarios, when applications don't properly manage query connections, or when the system is under heavy load.

What causes this error¶

You typically see it when:

• Too many concurrent requests come from your application
• Your application doesn't reuse connections and opens a new one for every request
• Long-running queries block new query execution
• A traffic spike sends more concurrent requests than usual

Example errors¶

SELECT * FROM events WHERE timestamp > '2024-01-01'
-- Error: Too many simultaneous queries

-- When trying to execute a new query while many are running
INSERT INTO events (user_id, event_type, timestamp) VALUES
(123, 'click', '2024-01-01 10:00:00')
-- Error: Too many simultaneous queries

-- Multiple applications trying to query simultaneously
SELECT COUNT(*) FROM events WHERE user_id = 123
-- Error: Too many simultaneous queries

How to fix it¶

Check current query count¶

Query system.processes to see what's running right now:

SELECT
    query_id,
    user,
    query,
    elapsed
FROM system.processes
ORDER BY start_time DESC

Check connection usage by user or token¶

Group by user to spot which token or integration is driving concurrency:

SELECT
    user,
    COUNT(*) as active_queries
FROM system.processes
GROUP BY user
ORDER BY active_queries DESC

Review request patterns over time¶

Query the tinybird.pipe_stats_rt Service Data Source to see request volume per API Endpoint and spot the traffic spikes that trigger this error:

SELECT
    pipe_name,
    COUNT(*) as requests,
    AVG(duration) as avg_duration
FROM tinybird.pipe_stats_rt
WHERE start_datetime >= now() - INTERVAL 1 HOUR
GROUP BY pipe_name
ORDER BY requests DESC

Manage concurrency in your application¶

Since you call Tinybird over the HTTP API, the fix lives in your application, not in ClickHouse® session settings:

• Reuse HTTP connections with a connection pool instead of opening a new one per request.
• Rate limit how many requests your application sends to Tinybird at once.
• Retry failed requests with exponential backoff instead of firing them again immediately.

import time

max_retries = 3
retry_delay = 1  # seconds

for attempt in range(max_retries):
    try:
        result = call_tinybird_endpoint()
        break
    except TooManySimultaneousQueriesError:
        if attempt < max_retries - 1:
            time.sleep(retry_delay)
            retry_delay *= 2
        else:
            raise

Tinybird-specific notes¶

Tinybird enforces concurrent query limits per Workspace. You only interact with Tinybird through the HTTP API, so you can't raise these limits yourself with ClickHouse® session settings like max_concurrent_queries. If your application already manages concurrency well and you're still hitting this error, contact support to discuss raising your Workspace's concurrency limits.

See also¶

• Service Data Sources
• Monitoring
• Pipes
• Support