The sharedbuffers configuration parameter sets the amount of memory the PostgreSQL server dedicates to its primary disk cache. This shared memory area is used to hold data pages (blocks) from tables and indexes that have been read from disk. By caching frequently accessed data in memory, PostgreSQL can significantly reduce disk I/O and improve query performance. It is one of the most critical performance-tuning parameters, as it directly impacts how effectively the database can serve data without accessing slower disk storage.

A. The amount of memory used for sorting operations is controlled by the workmem parameter, not sharedbuffers.

C. The Write-Ahead Log (WAL) buffer size is managed by a separate parameter, walbuffers.

D. The maximum number of client connections is determined by the maxconnections parameter, which is unrelated to the data cache.

1. PostgreSQL 16 Documentation, Chapter 20. Server Configuration, Section 20.4.1. Memory.

On sharedbuffers: "Sets the amount of memory the database server uses for shared memory buffers. The default is typically 128 megabytes (128MB)... This is the single most effective setting for improving performance..." This section explicitly defines its purpose as a cache for disk blocks.

On workmem: "Specifies the base maximum amount of memory to be used by a query operation (such as a sort or hash table) before writing to temporary disk files." This confirms workmem is for sorting, distinguishing it from sharedbuffers.

2. PostgreSQL 16 Documentation, Chapter 20. Server Configuration, Section 20.5.1. Settings.

On walbuffers: "Sets the amount of shared memory used for WAL data that has not yet been written to disk." This confirms a separate buffer exists for WAL data.

3. PostgreSQL 16 Documentation, Chapter 20. Server Configuration, Section 20.4.2. Connection and Authentication.

On maxconnections: "Determines the maximum number of concurrent connections to the database server." This confirms connection management is separate from sharedbuffers.