On September 12, 2015 5:18:28 PM PDT, Jeff Janes <jeff.ja...@gmail.com> wrote: >On Wed, Sep 2, 2015 at 5:32 AM, Andres Freund <and...@anarazel.de> >wrote: > >> On 2015-09-10 19:39:59 +0800, 张广舟(明虚) wrote: >> > We found there is a fsync call when CLOG buffer >> > is written out in SlruPhysicalWritePage(). It is often called when >a >> backend >> > needs to check transaction status with SimpleLruReadPage(). >> >> That's when there's not enough buffers available some other, and your >> case dirty, needs to be written out. >> > >Why bother to find a place to store the page in shared memory at all? >If >we just want to read it, and it isn't already in shared memory, then >why >not just ask the kernel for the specific byte we need? The byte we >want to >read can't differ between shared memory and kernel, because it doesn't >exist in shared memory.
I doubt that'd help - the next access would be more expensive, and we'd need to have a more complex locking regime. These pages aren't necessarily read only at that point. Andres --- Please excuse brevity and formatting - I am writing this on my mobile phone. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
