The shared_buffers parameter defines the size of the shared memory buffer cache. PostgreSQL uses this cache to store recently accessed data blocks. When a query needs data, it first checks shared_buffers. If the data is found (a cache hit), it's retrieved much faster than reading from disk. A common starting point is 25% of your system's RAM, but optimal values can vary based on workload and total available memory. Too high a value can starve the operating system's cache or other processes.

The work_mem parameter specifies the maximum amount of memory that can be used for internal sort operations and hash tables before writing to temporary disk files. This is critical for operations like ORDER BY, DISTINCT, and certain join types. If work_mem is too small, complex queries involving sorting or hashing will perform poorly. However, setting it too high can lead to memory exhaustion if many concurrent queries require large amounts of work_mem.

The max_connections parameter sets the upper limit on the number of concurrent client connections that PostgreSQL will accept. Each connection consumes some memory and system resources. Setting this too high can lead to resource exhaustion, while setting it too low can prevent legitimate users or applications from connecting. It's important to balance the number of connections with available system resources and the expected load.

The wal_buffers parameter determines the amount of memory used for WAL (Write-Ahead Logging) data before it is written to disk. WAL records are written before any changes are made to the actual data files, ensuring durability. A larger wal_buffers can improve write performance by allowing more WAL records to be buffered and written in larger chunks. However, it should not be excessively large, as it's allocated per server process.

The random_page_cost parameter is a cost estimate used by the query planner for fetching a disk page that is not sequentially accessed. By default, it's set to 4.0. If your storage system (e.g., SSDs) can access random pages much faster than this value suggests, lowering random_page_cost can make the planner favor index scans over sequential scans, which can be beneficial for certain workloads. However, setting it too low might lead to excessive index usage and inefficient plans.

The autovacuum_vacuum_threshold parameter (default 50) and autovacuum_analyze_threshold (default 50) determine the minimum number of rows that must be modified (updated or deleted) in a table before autovacuum will consider vacuuming or analyzing it. These are additive with autovacuum_vacuum_scale_factor and autovacuum_analyze_scale_factor. Tuning these thresholds can help ensure that tables are vacuumed and analyzed promptly without overwhelming the system with frequent vacuum operations on small tables.

The effective_cache_size parameter is a hint to the query planner about the total amount of memory that can be used for disk caching. It should be set to a value that reflects the sum of PostgreSQL's shared_buffers and the operating system's file system cache. The planner uses this value to estimate the cost of index scans versus sequential scans. A more accurate effective_cache_size can lead to better query plans, as the planner can more reliably predict whether data will be found in cache.

The log_min_duration_statement parameter is set to a time in milliseconds. Any SQL statement that takes longer than this duration to execute will be logged. Setting this to a reasonable value (e.g., 100ms or 500ms) is a powerful way to identify slow-running queries that might be impacting overall performance. These logged statements can then be analyzed and optimized.