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Parameter Formula
Last updated: 2023-12-13 10:18:41
TDSQL-C for MySQL now allows certain parameters to use formulaic values for smarter database adaptation. When the instance specifications are adjusted, such parameter values will also be automatically adjusted accordingly, ensuring optimal status or stability of the database.
Notice
The parameter formula is only applicable to parameters with numerical values. Formulaic values are not supported for parameters of other data types.
Upon the setting of formulaic parameter values, these values will change in accordance with the instance specification adjustment. If the calculated parameter value resulting from your formula exceeds the parameter value range (minimum value to maximum value), the parameter value will be set to the nearest boundary value within this range. That is, if it is smaller than the minimum value, the parameter will adopt the minimum value. If it exceeds the maximum value, the parameter will adopt the maximum value.
Example:
A parameter, as calculated by the configured formula, results in a value of 7. However, the specified range for the parameter is 1 to 6. In this case, the final value assigned to the parameter will be 6.
A parameter, as calculated by the configured formula, results in a value of 5. However, the specified range for the parameter is 6 to 10. In this case, the final value assigned to the parameter will be 6.
When export from or import from configuration files is configured, formula-based parameter values are not supported. During export, they will automatically be adjusted to integer values.
To ensure the availability of the database, only a select set of parameters currently accommodates formulaic configurations. For more parameters, see upcoming iterations.
Parameter Formula Description
Parameter Formula Composition | Name | Description |
Variable | DBinitMemory | The memory size of the instance specification represented as an integer, in the unit of MB. |
| DBInitCpu | The number of CPU cores in the instance specification, represented as an integer, in the unit of cores. |
Operator | Division operator (/) | Divides the dividend by the divisor to return an integer quotient. If the result is a decimal, the integral part is used. |
| Multiplication operator (*) | The product of two factors is returned as an integer. If the result is a decimal, the integral part is used. |
Function | MIN() | Returns the smallest value in the form of an integer or parameter formula list. |
| MAX() | Returns the greatest value in the form of an integer or parameter formula list. |
Example:
The MAX(DBInitCpu/2,4) function indicates that the number of CPU cores of the instance divided by 2 is compared with 4 and the larger value is returned.
Parameters Supporting Parameter Formula
The following parameters support parameter formula in the current version. You can modify default formulas according to your business requirements.
Parameter | Description | Default Formula |
binlog_cache_size | The size of the memory buffer used to store binary logs of adjustments during the transaction. | MIN(DBInitMemory/4000 * 32768,2097152) |
max_heap_table_size | This variable sets the maximum size of user-created tables in the memory. | MIN( DBInitMemory/1000 * 4194304,134217728) |
innodb_buffer_pool_size | The size (in bytes) of the buffer pool, which is the memory area of InnoDB cache table and index data. | min((DBInitMemory - 500), DBInitMemory*3/4)*1000000 |
innodb_buffer_pool_instances | The number of regions divided according to the InnoDB cache pools. | MIN(DBInitMemory/2000,16) |
innodb_read_io_threads | The number of I/O threads in InnoDB used for read operations. | MAX(DBInitCpu/2,4) |
innodb_write_io_threads | The number of I/O threads in InnoDB used for write operations. | MAX(DBInitCpu/2,4) |
join_buffer_size | The minimum size of the cache for table joins used in common index scans, range index scans, and full table scans. | MIN(DBInitMemory*128,262144) |
max_connections | The maximum number of connections. | MIN(DBInitMemory/4+500,100000) |
table_definition_cache | The number of opened table cache instances. | MAX(DBInitMemory*512/1000,2048) |
table_open_cache | The size of table descriptor cache, which can reduce the number of times the files are opened and closed. | MIN(MAX(DBInitMemory*512/1000,2048), 65536) |
table_open_cache_instances | The number of partitions for the MySQL table handle cache. | MIN(DBInitMemory/1000,16) |
thread_pool_size | This parameter indicates the number of thread groups in the thread pool. By default, the number of thread groups equals the number of CPUs. | MIN(DBInitCpu,64) |
thread_cache_size | The number of threads that should be retained in the cache for reuse. | MIN(DBInitMemory/125+8,512) |
tmp_table_size | The maximum size of the internal memory temporary table. | MIN(DBInitMemory/1000*4194304,134217728) |
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