ClickHouse High Memory Usage

ch_memory_high.md

To investigate high RAM usage in ClickHouse and determine what's consuming so much memory, you can try the following steps:

1. Check system tables: Query the system.metrics and system.asynchronous_metrics tables to get an overview of memory usage:

   SELECT * FROM system.metrics WHERE metric LIKE '%Memory%';
   SELECT * FROM system.asynchronous_metrics WHERE metric LIKE '%Memory%';

2. Examine query memory usage: Look at currently running queries and their memory consumption:

   SELECT query_id, user, elapsed, memory_usage
   FROM system.processes
   ORDER BY memory_usage DESC;

3. Check table sizes: Identify large tables that might be causing memory pressure:

   SELECT database, name, total_bytes, total_rows
   FROM system.tables
   ORDER BY total_bytes DESC
   LIMIT 10;

4. Review merge processes: Check if there are any large merges in progress:

   SELECT * FROM system.merges;

5. Inspect background processes: Look at background processes that might be consuming memory:

   SELECT * FROM system.background_processing_pool;