Magnus,
That shows that you don't really know how the memory manager in NT+ works ;-) *ALL* normal file I/O is handled through the memory manager :-) So yes, they are both different access methods to the memory manager, really.
"don't really" is a overstatement, I do not know at all how the memory manager works in NT+. All I learned is "Inside Windows NT" of H. Custer from 1993 :) So, just to make sure I understood correctly: If PostgreSQL reads a file from disk, Windows NT does this file I/O though the same memory manager than when PostgreSQL puts parts of this read file [for example an index segment] into shared memory - which is nothing but a file, that usually stays in main memory. Correct so far? I continued from this thoughts: lets say there is 500MB memory available, we have 100MB of shared_memory configured. Now PostgreSQL reads 100MB from a file - memory manager takes 100MB memory to fullfill this file access (optimizations aside) Now PostgreSQL reshuffles that 100MB and decides: "hmmmm, that may be valuable for ALL of the currently running postgres.exe" and pushes those 100MB into shared memory for all to use. It caches the 100MB - a fine chunk of an index.
