system.settings
Contains information about session settings for current user.
mysql> SELECT * FROM system.settings;
+------------------------------------+-----------+---------------+--------------------------------------------------------------------------------------------------------------------------------------------+
| name | value | default_value | description |
+------------------------------------+-----------+---------------+--------------------------------------------------------------------------------------------------------------------------------------------+
| storage_read_buffer_size | 1048576 | 1048576 | The size of buffer in bytes for buffered reader of dal. By default, it is 1MB. |
| min_distributed_rows | 100000000 | 100000000 | Minimum distributed read rows. In cluster mode, when read rows exceeds this value, the local table converted to distributed query. |
| max_threads | 16 | 16 | The maximum number of threads to execute the request. By default, it is determined automatically. |
| flight_client_timeout | 60 | 60 | Max duration the flight client request is allowed to take in seconds. By default, it is 60 seconds |
| parallel_read_threads | 1 | 1 | The maximum number of parallelism for reading data. By default, it is 1. |
| storage_occ_backoff_init_delay_ms | 5 | 5 | The initial retry delay in millisecond. By default, it is 5 ms. |
| max_block_size | 10000 | 10000 | Maximum block size for reading |
| min_distributed_bytes | 524288000 | 524288000 | Minimum distributed read bytes. In cluster mode, when read bytes exceeds this value, the local table converted to distributed query. |
| storage_occ_backoff_max_delay_ms | 20000 | 20000 | The maximum back off delay in millisecond, once the retry interval reaches this value, it stops increasing. By default, it is 20 seconds. |
| storage_occ_backoff_max_elapsed_ms | 120000 | 120000 | The maximum elapsed time after the occ starts, beyond which there will be no more retries. By default, it is 2 minutes |
+------------------------------------+-----------+---------------+--------------------------------------------------------------------------------------------------------------------------------------------+
Examples：
E1： Change number of parallelism for reading data， This is good for performance.
set parallel_read_threads=8;
E2: Limit the CPU usage of a query
set max_threads = N;
E3： Change Read buffer size 2M
storage_read_buffer_size=2097152;