Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1?

On Nov 16, 2010, at 4:05 PM, Mladen Gogala wrote:

> Josh Berkus wrote:
>> On 11/16/10 12:39 PM, Greg Smith wrote:
>>
>>> I want to next go through and replicate some of the actual database
>>> level tests before giving a full opinion on whether this data proves
>>> it's worth changing the wal_sync_method detection. So far I'm torn
>>> between whether that's the right approach, or if we should just increase
>>> the default value for wal_buffers to something more reasonable.
>>>
>>
>> We'd love to, but wal_buffers uses sysV shmem.
>>
>>
> Speaking of the SYSV SHMEM, is it possible to use huge pages?

RHEL 6 and friends have transparent hugepage support. I'm not sure if they yet transparently do it for SYSV SHMEM, but they do for most everything else. Sequential traversal of a process heap is several times faster with hugepages. Unfortunately, postgres doesn't organize its blocks in its shared_mem to be sequential for a relation. So it might not matter much.

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