Debugging memory issues

Queries to help you debug memory issues.

When encountering memory issues or a memory leak, knowing what queries and resources are consuming a significant amount of memory is helpful. Below you can find queries that can help you to debug memory issues by finding which queries, databases, and tables can be optimized:

List currently running processes by peak memory usage

SELECT
    initial_query_id,
    query,
    elapsed,
    formatReadableSize(memory_usage),
    formatReadableSize(peak_memory_usage),
FROM system.processes
ORDER BY peak_memory_usage DESC
LIMIT 100;

List metrics for memory usage

SELECT
    metric, description, formatReadableSize(value) size
FROM
    system.asynchronous_metrics
WHERE
    metric LIKE '%Cach%'
    OR metric LIKE '%Mem%'
ORDER BY
    value DESC;

List tables by current memory usage

SELECT
    database,
    name,
    formatReadableSize(total_bytes)
FROM system.tables
WHERE engine IN ('Memory','Set','Join');

Output total memory used by merges

SELECT formatReadableSize(sum(memory_usage)) FROM system.merges;

Output total memory used by currently running processes

SELECT formatReadableSize(sum(memory_usage)) FROM system.processes;

Output total memory used by dictionaries

SELECT formatReadableSize(sum(bytes_allocated)) FROM system.dictionaries;

Output total memory used by primary keys and index granularity

SELECT
    sumIf(data_uncompressed_bytes, part_type = 'InMemory') AS memory_parts,
    formatReadableSize(sum(primary_key_bytes_in_memory)) AS primary_key_bytes_in_memory,
    formatReadableSize(sum(primary_key_bytes_in_memory_allocated)) AS primary_key_bytes_in_memory_allocated,
    formatReadableSize(sum(index_granularity_bytes_in_memory)) AS index_granularity_bytes_in_memory,
    formatReadableSize(sum(index_granularity_bytes_in_memory_allocated)) AS index_granularity_bytes_in_memory_allocated
FROM system.parts;