Scott Carey wrote:
As long as fsync() works _properly_ which is true for any file system + disk combination
with a damn (not HFS+ on OSX, not FAT, not a few other things), then it will tell the
drive to flush its cache _before_ fsync() returns. There is NO REASON for a raid card to
turn off a
> I'd suggest to increase the value up to ~80MB, if not for the system,
> may be just for the session running this query.
> Then see if performance improved.
Don't forget you can do this for the given query without affecting the
other queries - just do something like
SET work_mem = 128M
and the
> -Original Message-
> From: Patrick Donlin [mailto:pdon...@oaisd.org]
> Sent: Thursday, July 15, 2010 11:13 AM
> To: Kevin Grittner; pgsql-performance@postgresql.org
> Subject: Re: Identical query slower on 8.4 vs 8.3
>
> I'll read over that wiki entry, but for now here is the
> EXPL
On 16/07/10 09:22, Scott Marlowe wrote:
> On Thu, Jul 15, 2010 at 10:30 AM, Scott Carey wrote:
>>
>> On Jul 14, 2010, at 7:50 PM, Ben Chobot wrote:
>>
>>> On Jul 14, 2010, at 6:57 PM, Scott Carey wrote:
>>>
But none of this explains why a 4-disk raid 10 is slower than a 1 disk
system.
On 16/07/10 06:18, Ben Chobot wrote:
> There are also caches on all your disk drives. Write caching there is always
> dangerous, which is why almost all raid cards always disable the hard drive
> write caching, with or without a BBU. I'm not even sure how many raid cards
> let you enable the wr
On Jul 15, 2010, at 8:16 PM, Scott Carey wrote:
> On Jul 15, 2010, at 12:35 PM, Ben Chobot wrote:
>
>> On Jul 15, 2010, at 9:30 AM, Scott Carey wrote:
>>
Many raid controllers are smart enough to always turn off write caching on
the drives, and also disable the feature on their own bu
On Jul 15, 2010, at 6:22 PM, Scott Marlowe wrote:
> On Thu, Jul 15, 2010 at 10:30 AM, Scott Carey wrote:
>>
>> On Jul 14, 2010, at 7:50 PM, Ben Chobot wrote:
>>
>>> On Jul 14, 2010, at 6:57 PM, Scott Carey wrote:
>>>
But none of this explains why a 4-disk raid 10 is slower than a 1 disk
On Jul 15, 2010, at 12:35 PM, Ben Chobot wrote:
> On Jul 15, 2010, at 9:30 AM, Scott Carey wrote:
>
>>> Many raid controllers are smart enough to always turn off write caching on
>>> the drives, and also disable the feature on their own buffer without a BBU.
>>> Add a BBU, and the cache on the
On Thu, Jul 15, 2010 at 10:30 AM, Scott Carey wrote:
>
> On Jul 14, 2010, at 7:50 PM, Ben Chobot wrote:
>
>> On Jul 14, 2010, at 6:57 PM, Scott Carey wrote:
>>
>>> But none of this explains why a 4-disk raid 10 is slower than a 1 disk
>>> system. If there is no write-back caching on the RAID, it
Most (all?) hard drives have cache built into them. Many raid cards have
cache built into them. When the power dies, all the data in any cache is
lost, which is why it's dangerous to use it for write caching. For that
reason, you can attach a BBU to a raid card which keeps the cache alive
On Thu, Jul 15, 2010 at 12:35 PM, Ben Chobot wrote:
> On Jul 15, 2010, at 9:30 AM, Scott Carey wrote:
>
> >> Many raid controllers are smart enough to always turn off write caching
> on the drives, and also disable the feature on their own buffer without a
> BBU. Add a BBU, and the cache on the c
On Jul 15, 2010, at 2:40 PM, Ryan Wexler wrote:
> On Thu, Jul 15, 2010 at 12:35 PM, Ben Chobot wrote:
> On Jul 15, 2010, at 9:30 AM, Scott Carey wrote:
>
> >> Many raid controllers are smart enough to always turn off write caching on
> >> the drives, and also disable the feature on their own bu
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