On Mon, May 28, 2012 at 8:15 AM, Waldecir Faria <[email protected]> wrote: > Good morning, I am doing a study about buffer management to improve the > performance of one program that does heavy I/O operations. After looking and > reading from different softwares' source codes/texts one friend suggested me > to take a look at the PostgreSQL code. I already took a look at the > PostgreSQL buffer management modules ( freelist.c and cia ) but now I am a > bit confused how the buffer read/write works, I tried to see how PostgreSQL > does to get, for example, a char array from one buffer. Looking at rawpage.c > I think that I found a good example using the following function calls > sequence starting at function get_raw_page_internal(): > > StrategyGetBuffer->BufferAlloc->ReadBuffer_Common > ->ReadBufferExtended->BufferGetPage-> memcpy page to buf
BufferGetPage() doesn't copy anything; it just takes the buffer number and returns a pointer to the address of that buffer in memory. More generally, that whole chain of function calls has to do with how a page ends up inside PostgreSQL's buffer cache, not with how anything on the page is actually decoded. Each buffer contains zero or more tuples; each tuple contains multiple attributes. So after you get the buffer you have to iterate over the tuples and then decode each tuple to get the values that you want. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list ([email protected]) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
