On Fri, 2002-10-04 at 18:03, Neil Conway wrote: > "Curtis Faith" <[EMAIL PROTECTED]> writes: > > It looks to me like BufferAlloc will simply result in a call to > > BufferReplace > smgrblindwrt > write for md storage manager objects. > > > > This means that a process will block while the write of dirty cache > > buffers takes place. > > I think Tom was suggesting that when a buffer is written out, the > write() call only pushes the data down into the filesystem's buffer -- > which is free to then write the actual blocks to disk whenever it > chooses to. In other words, the write() returns, the backend process > can continue with what it was doing, and at some later time the blocks > that we flushed from the Postgres buffer will actually be written to > disk. So in some sense of the word, that I/O is asynchronous.
Isn't that true only as long as there is buffer space available? When there isn't buffer space available, seems the window for blocking comes into play?? So I guess you could say it is optimally asynchronous and worse case synchronous. I think the worse case situation is one which he's trying to address. At least that's how I interpret it. Greg
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