Re: Amazon High I/O instances

One more question .. I could not set wal_sync_method to anything else but
fsync .. is that expected or should other choices be also available ? I am
not sure how the EC2 SSD cache flushing is handled on EC2, but I hope it is
flushing the whole cache on every sync .. As a side note, I got corrupted
databases (errors about pg_xlog directories not found, etc) at first when
running my tests, and I suspect it was because of
vfs.zfs.cache_flush_disable=1, though I cannot prove it for sure.

Sébastien

On Wed, Sep 12, 2012 at 8:49 PM, Sébastien Lorion
<sl(at)thestrangefactory(dot)com>wrote:

> Is dedicating 2 drives for WAL too much ? Since my whole raid is comprised
> of SSD drives, should I just put it in the main pool ?
>
> Sébastien
>
>
> On Wed, Sep 12, 2012 at 8:28 PM, Sébastien Lorion <
> sl(at)thestrangefactory(dot)com> wrote:
>
>> Ok, make sense .. I will update that as well and report back. Thank you
>> for your advice.
>>
>> Sébastien
>>
>>
>> On Wed, Sep 12, 2012 at 8:04 PM, John R Pierce <pierce(at)hogranch(dot)com>wrote:
>>
>>> On 09/12/12 4:49 PM, Sébastien Lorion wrote:
>>>
>>>> You set shared_buffers way below what is suggested in Greg Smith book
>>>> (25% or more of RAM) .. what is the rationale behind that rule of thumb ?
>>>> Other values are more or less what I set, though I could lower the
>>>> effective_cache_size and vfs.zfs.arc_max and see how it goes.
>>>>
>>>
>>> I think those 25% rules were typically created when ram was no more than
>>> 4-8GB.
>>>
>>> for our highly transactional workload, at least, too large of a
>>> shared_buffers seems to slow us down, perhaps due to higher overhead of
>>> managing that many 8k buffers. I've heard other read-mostly workloads,
>>> such as data warehousing, can take advantage of larger buffer counts.
>>>
>>>
>>>
>>>
>>> --
>>> john r pierce N 37, W 122
>>> santa cruz ca mid-left coast
>>>
>>>
>>>
>>>
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>>
>>
>