Christopher Browne wrote:
This is misleading: PAE means that a 32-bit cpu can have more that 4 GB physical memory. Each process can map at most 4 (in reality: ~2) GB memory.The "fix" for this problem is to rewrite all of your applications so that they become conscious of which bits of memory they're using so they can tune their own behaviour. This, of course, requires discarding useful notions such as "virtual memory" that are _assumed_ by most modern operating systems.
Many databases manage their own, huge buffer pool and read/write the database tables with O_DIRECT. These apps must support buffer pools > 2 GB, which requires some work. Linux and Solaris contain a special syscall that helps Oracle to manage it's buffer pool for such setups (remap_page_rage()).
OTHO postgres has a small user space buffer pool, the majority of the file buffers are handled by OS. Thus no changes are required inside postgres for PAE, all it needs is an OS that support PAE for the buffer pool.
Regarding hyperthreading: I'm aware of two changes:
- busy loops must contain PAUSE instructions. Postgres does that.
- virtual aliases should be avoided: If two processes access memory at the same virtual address, then this can cause cache collisions and then misses. I think this is handled by the C library by randomizing the return addresses of malloc() and Intel mitigated the issue by improving the cache.
-- Manfred
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