On Tue, Nov 20, 2018 at 11:11 PM REIX, Tony <tony.r...@atos.net> wrote: > On AIX, since with MMAP we have only 4K pages though we can have 64K pages > with SYSV, we'd like to experiment with SYSV rather than MMAP and measure the > impact to the performance. > > Looking at file: src/include/storage/dsm_impl.h , it seemed to me that > replacing the line: > > #define DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE DSM_IMPL_POSIX > by the line: > #define DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE DSM_IMPL_SYSV
Hi Tony, SHOW dynamic_shared_memory_type to see which one it's actually using, and set it in postgresql.conf to change it. > However, when looking at details by means of procmap tool, it is unclear if > that worked or not. These segments are short-lived ones used for parallel query. I haven't used AIX recently but I suspect procmap -X will show them as different types and show the page size, but you'd have to check that while it's actually running a parallel query. For example, a large parallel hash join that runs for a while would do it, and in theory you might be able to see a small performance improvement for larger page sizes due to better TLB cache hit ratios. -- Thomas Munro http://www.enterprisedb.com
