Cache Buffer Chains (CBC) is a mechanism used by the PostgreSQL storage engine to manage the buffer cache and minimize the amount of disk I/O. The buffer cache is a region of memory that is used to store frequently accessed data pages from the disk.
In CBC, data pages are grouped into chains, and each chain represents a set of pages that are related in some way, such as belonging to the same table or index. When a page is accessed, the entire chain is loaded into memory, reducing the number of disk I/O operations.
In PostgreSQL 16, CBC has been improved and optimized for better performance. The CBC mechanism has been updated to work more efficiently with modern hardware and the latest operating systems, which results in faster and more consistent performance.
Additionally, the CBC mechanism now includes a new function called pg_buffercache_pages() that allows you to see the number of pages that are currently in the buffer cache, which can help you monitor and optimize the performance of your PostgreSQL system.
Overall, the improvements to CBC in PostgreSQL 16 make it a more efficient and effective mechanism for managing the buffer cache and minimizing disk I/O operations.
How pg_buffercache_pages() is implemented in PostgreSQL 16?
pg_buffercache_pages() is implemented as a built-in function in PostgreSQL 16. It allows you to query the status of the buffer cache in PostgreSQL and provides information about the number of pages that are currently in memory.
The function returns a row for each page in the buffer cache, with columns for the relation ID, block number, and the state of the page (such as “clean,” “dirty,” or “frozen”).
Here’s a basic example of how to use pg_buffercache_pages():
SELECT * FROM pg_buffercache_pages();
This query returns a row for each page in the buffer cache, with columns for the relation ID, block number, and the state of the page. You can use this information to monitor and optimize the performance of your PostgreSQL system.
Note: The pg_buffercache_pages() function is only available in PostgreSQL 16 or later. In earlier versions of PostgreSQL, you can obtain similar information using other methods, such as the pg_stat_bgwriter view.