Depending on the location of table blocks in the buffer cache performance may be affected (Ex : Tables blocks scattered across all the nodes or clustered on one node). In this blog post i will show quickly how to map table blocks to NUMA nodes based on my previous work done in this blog post.(Mapping ORACLE SGA components to numa nodes using NUMA API)
In my previous blog post i showed how we can display memory components (Buffer cache,Shared pool,Large Pool,etc) distribution across the different NUMA nodes using the NUMA API. But what to do if we want to have more control ? Can we for example isolate a specific SGA components in a specific set of nodes ?
Suppose for example that you are using the IN-MEMORY column store and only a few user are relying heavily on it.Would it be useful to collocate them on a specific set of nodes to improve memory access latency.For sure it depend ! But we can do it ! Using the NUMA API and specifically the function “move_pages” we can distribute the memory pages across NUMA nodes as we want !
Automatic NUMA Balancing which is enabled by default on UEK R4 rely on a similar mechanism for moving the memory pages closer to where the task is executing.(For more info check this) but it does not support for now the migration of Huge Pages (hugetlbfs)
[root@svltest ~]# sysctl -a | grep numa_balancing
kernel.numa_balancing = 1
kernel.numa_balancing_scan_delay_ms = 1000
kernel.numa_balancing_scan_period_max_ms = 60000
kernel.numa_balancing_scan_period_min_ms = 1000
kernel.numa_balancing_scan_size_mb = 256
This is what we are going to achieve in this blog post :
How every SGA component (Buffer cache,Shared pool,Large Pool,etc) is distributed across NUMA nodes after initial startup ? And what it will look like after dynamically shrinking or growing of memory area ? In this post i will show a way to display memory components distribution across the different NUMA nodes using the NUMA API.
If you upgraded to the new Unbreakable Enterprise Kernel Release 4,then if you take a quick look at the I/O scheduler used by your block devices this is what you will see :
cat /sys/block/sdb/queue/scheduler none
none !! what ?
As you may know Unbreakable Enterprise Kernel Release 4 is finally here with many enhancement.So If you plan to upgrade your kernel to UEK4 and you are using Huge page for your database (And you probably should) you “may” see a great improvements in start-up times. So what have changed ?