TiDB `tidb_mem_quota_query` Parameter: Controlling Query Memory Usage

The tidb_mem_quota_query parameter is a configuration setting in TiDB, an open-source distributed NewSQL database, that defines the maximum amount of memory allowed for query execution.

TiDB employs a two-tier memory management system: global memory and local memory. The tidb_mem_quota_query parameter specifically regulates the maximum memory that can be allocated for query processing within the global memory pool. This includes memory used for storing intermediate results, sorting, joining, aggregating, and other query-related operations.

By adjusting the tidb_mem_quota_query value, users can control the memory usage during query execution, preventing excessive consumption that might lead to performance degradation or out-of-memory errors. The default value for this parameter is 32GB.

It's important to note that tidb_mem_quota_query is a dynamic configuration parameter, allowing modification during runtime without needing to restart the TiDB server. However, changing this value can impact the performance of active queries, so adjustments should be made cautiously considering available system resources and workload characteristics.