In PostgreSQL, the max_parallel_workers_per_gather parameter determines the maximum number of parallel workers that can be used for a single GATHER operation. This parameter controls the maximum degree of parallelism for GATHER operations, which are used to collect data from multiple parallel workers and combine it into a single result.

The max_parallel_workers_per_gather parameter is an integer value that specifies the maximum number of parallel workers that can be used for a single GATHER operation. The default value for this parameter is 8, which means that by default, PostgreSQL will use up to eight parallel workers for a single GATHER operation.

You can adjust the value of the max_parallel_workers_per_gather parameter to control the maximum degree of parallelism for GATHER operations in your PostgreSQL database. For example, if you set this parameter to 16, PostgreSQL will use up to 16 parallel workers for a single GATHER operation.

Overall, the max_parallel_workers_per_gather parameter is an important configuration setting that can affect the performance and scalability of your PostgreSQL database. By controlling the maximum degree of parallelism for GATHER operations, you can fine-tune the performance of your database and ensure that it is able to handle high-volume workloads and large amounts of data efficiently.

To tune the max_parallel_workers_per_gather parameter in PostgreSQL, you will need to do the following:

1. Identify the workload and data characteristics of your PostgreSQL database, such as the type and volume of queries that are run, the size and distribution of data, and the hardware and network resources available.

2. Measure the performance of your PostgreSQL database with different values for the max_parallel_workers_per_gather parameter, using a workload that is representative of your actual usage.

3. Compare the performance results and determine the optimal value for the max_parallel_workers_per_gather parameter that provides the best balance of performance and resource utilization for your workload and data.

4. Adjust the value of the max_parallel_workers_per_gather parameter in your PostgreSQL configuration to the optimal value determined in step 3.

5. Monitor the performance of your PostgreSQL database after adjusting the max_parallel_workers_per_gather parameter to ensure that it is providing the expected benefits and that there are no unexpected performance issues.

Overall, tuning the max_parallel_workers_per_gather parameter in PostgreSQL involves a combination of workload analysis, performance measurement, and configuration adjustment. By following the steps outlined above, you can determine the optimal value for this parameter and ensure that your PostgreSQL database is able to handle your workload and data efficiently and effectively.