Setting and Querying KOVAE Parameters and Querying Status Variables

You can configure KOVAE parameters by using the database startup command line, the configuration file, or the dynamic modification during the running of MySQL. Three status variables kovae_enter_times, kovae_execution_times, and kovae_execution_succeed_times are added to KOVAE to check KOVAE-related statistics.

Setting and Querying KOVAE Parameters

Table 1 describes the KOVAE parameters.

**Table 1** KOVAE parameters
Parameter	Support Startup Command Line Parameters or Not	Support Startup Configuration Files or Not	Support Dynamic Modification or Not	Application Scope	Type	Default Value	Value Range	Description
secondary_engine_cost_threshold	Yes	Yes	Yes	Global	double	100000	0-DBL_MAX (maximum double value)	Queries the cost threshold for using the secondary engine. When the cost is greater than the cost threshold, the secondary engine will be used for the query execution.
innodb_parallel_read_threads	Yes	Yes	Yes	Session	unsigned long	4	1–256	Indicates the number of threads that concurrently read a table.
kovae_aggregator_hash_type	Yes	Yes	Yes	Session	unsigned int	0	0 and 1	Indicates the working mode of the Agg operator during hash grouping. 0 indicates that all worker threads share a hash table. 1 indicates that each worker thread uses its own hash table. When the number of grouping records is large and the number of grouping result records is small, using mode 1 has a significant improvement effect. When the number of grouping records and the number of grouping result records are both large (the number of grouping result records is far greater than the number of parallel threads of the current query), mode 0 is recommended.
kovae_hashjoin_batch_num	Yes	Yes	Yes	Session	unsigned long	1024	128-4096	Indicates the maximum number of partitions in a hash table.
kovae_log_level	Yes	Yes	Yes	Global	unsigned int	2	1–5	Indicates the log output level. The log levels and their corresponding values are as follows: ERR: 1 WARNING: 2 NOTICE: 3 INFO: 4 DEBUG: 5 After the log output level is set, logs whose levels are lower than or equal to the configured value will be generated in the error log file of MySQL.
kovae_memory_buffer_size	Yes	Yes	Yes	Session	unsigned longlong	1073741824	268435456-2⁶⁴-1 (maximum unsigned long long value)	If the memory used by the Sort, Aggregation, HashJoin, and Materialize operators exceeds the number of bytes of the configured value, the flushing process is triggered to reduce the memory usage, which may affect the performance.
kovae_memory_control	Yes	Yes	Yes	Global	bool	0	0 and 1	Indicates the main switch of the memory control function. If this parameter is disabled, the memory for parallel queries tends to be requested from the OS. If this parameter is enabled, the memory that can be requested for parallel queries is controlled by the value of kovae_memory_max_size, and all the memory requests for parallel queries from the OS are counted and monitored.
kovae_memory_max_size	Yes	Yes	Yes	Global	longlong	10*2^30	2³⁰-2⁶³-1 (maximum long long value)	Indicates the total memory that can be requested for parallel queries. The value of kovae_memory_max_size takes effect only after kovae_memory_control is enabled. If the total number of bytes of the memory requested for all query statements exceeds the value of kovae_memory_max_size, the system cannot continue the parallel query process and memory requests may fail. In this case, the query process automatically exits. NOTE: The memory control is not strict to single byte, and there may be certain errors. The precision of memory control is affected by the operators and number of parallel queries. The value of kovae_memory_max_size must be less than the available memory to ensure that there is reserved memory.
kovae_memory_save_num	Yes	Yes	Yes	Global	unsigned int	100	0–1000	Configures the number of latest parallel query records that can be cached in the information_schema.KOVAE_MEMORY_HISTORY table. After memory control for parallel queries is enabled, you can check historical memory usage records by checking the information_schema.KOVAE_MEMORY_HISTORY table.
kovae_serial_mode	Yes	Yes	Yes	Global	bool	0	0 and 1	Specifies whether to enable the serial mode. After this parameter is enabled, only one SQL statement can be executed for a query.
kovae_threadpool_size	Yes	Yes	Yes	Global	unsigned int	Number of CPU cores. If the number of CPU cores fails to be obtained, the value is 1.	1–65535	Indicates the maximum number of threads that can be reserved in the thread pool. All working threads for parallel queries are requested from the thread pool. When the number of threads in the thread pool is used up, new thread requests are restricted by the kovae_threadpool_stalltime parameter. When the number of requested threads reaches the value of kovae_threadpool_size, new threads can only be requested after the interval specified by kovae_threadpool_stalltime. Generally, the value of kovae_threadpool_size can be set to three to five times the number of available CPU cores.
kovae_parallel_threads	Yes	Yes	Yes	Session	unsigned int	2	1-1000	Indicates the maximum number of working threads that can be requested in a single parallel query. Generally, kovae_parallel_threads can be set to the value of kovae_threadpool_size/Number of parallel queries and sessions that are simultaneously executed with a high probability.
kovae_threadpool_stalltime	Yes	Yes	Yes	Global	unsigned int	1800	0-2³²-1 (maximum unsigned int value)	When all threads in the thread pool are requested and there are no idle threads, new queries cannot obtain available worker threads. To avoid excessive thread creation and resource waste, a waiting time parameter kovae_threadpool_stalltime is set. Only when the time of two failed requests exceeds the waiting time (in seconds), a new worker thread is created for new parallel queries. Retain the default value of kovae_threadpool_stalltime.
kovae_statement_history_schema_size	Yes	Yes	No	Global	unsigned longlong	10000	100-2⁶³-1 (maximum long long value)	Indicates the maximum number of cached rows in the INFORMATION_SCHEMA.KOVAE_STATEMENT_HISTORY table. The recorded cache is applied for allocation when KOVAE is loaded and released when KOVAE is uninstalled.
kovae_threads_history_schema_size	Yes	Yes	No	Global	unsigned longlong	100000	10000-2⁶³-1 (maximum long long value)	Indicates the maximum number of cached rows in the INFORMATION_SCHEMA.KOVAE_THREADS_HISTORY table. The recorded cache is applied for allocation when KOVAE is loaded and released when KOVAE is uninstalled.
kovae_memory_detail_history_schema_size	Yes	Yes	No	Global	unsigned longlong	1000000	10000-2⁶³-1 (maximum long long value)	Indicates the maximum number of cached rows in the INFORMATION_SCHEMA.KOVAE_MEMORY_DETAIL_HISTORY table. The recorded cache is applied for allocation when KOVAE is loaded and released when KOVAE is uninstalled.
kovae_buffer_detail_history_schema_size	Yes	Yes	No	Global	unsigned longlong	1000000	10000-2⁶³-1 (maximum long long value)	Indicates the maximum number of cached rows in the INFORMATION_SCHEMA.KOVAE_BUFFER_DETAIL_HISTORY table. The recorded cache is applied for allocation when KOVAE is loaded and released when KOVAE is uninstalled.
kovae_memory_detail_rowadapter	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the rowadapter operator collects statistics on memory requests and release. If this parameter is enabled, the operator performance slightly deteriorates.
kovae_memory_detail_tablescan	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the Tablescan operator collects statistics on memory requests and release.
kovae_memory_detail_indexrangescan	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the index range scan operator collects statistics on memory requests and release.
kovae_memory_detail_indexscan	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the index scan operator collects statistics on memory requests and release.
kovae_memory_detail_agg	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the Agg operator collects statistics on memory requests and release.
kovae_memory_detail_material	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the Materialize operator collects statistics on memory requests and release.
kovae_memory_detail_sort	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the Sort operator collects statistics on memory requests and release.
kovae_memory_detail_hashjoin	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the HashJoin operator collects statistics on memory requests and release.
kovae_memory_detail_limit	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the Limit operator collects statistics on memory requests and release.
kovae_memory_detail_nestedloopjoin	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the NestedLoopJoin operator collects statistics on memory requests and release.
kovae_memory_detail_streaming	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the Streaming operator collects statistics on memory requests and release.
kovae_buffer_view_tablescan	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the table scan operator collects statistics on cache usage and release.
kovae_buffer_view_agg	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the Agg operator collects statistics on cache usage and release.
kovae_buffer_view_sort	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the Sort operator collects statistics on cache usage and release.
kovae_buffer_view_hashjoin	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the HashJoin operator collects statistics on cache usage and release.
kovae_buffer_view_material	Yes	Yes	Yes	Global	bool	false	true and false	Indicates whether the Materialize operator collects statistics on cache usage and release.

Run the following command to set KOVAE parameters:

set variable Parameter_name=Parameter_value;
set global variable Parameter_name=Parameter_value;

Run the following command to check the configured KOVAE parameters:
```
show variables like "%Parameter_name%";
```

Querying Status Variables

Three status variables listed in Table 2 are added to KOVAE to check KOVAE-related statistics.

**Table 2** Status variables
Status Variable	Description
kovae_enter_times	Indicates the number of SQL statements that access KOVAE.
kovae_execution_times	Indicates the number of SQL statements filtered by the allowlist control and executed in KOVAE.
kovae_execution_succeed_times	Indicates the number of SQL statements that have been executed in KOVAE.

Log in to the MySQL service through the MySQL client.
Run the following command to query the value of a status variable:
```
show status like "%Status_variable%";
```

Parent topic: Feature Usage