| Lists: | pgsql-hackers |
|---|
| From: | Josh Berkus <josh(at)agliodbs(dot)com> |
|---|---|
| To: | PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org> |
| Subject: | What happened to open_sync_without_odirect? |
| Date: | 2011-01-15 22:15:53 |
| Message-ID: | 4D321C99.9060405@agliodbs.com |
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| Lists: | pgsql-hackers |
Last I remember, we were going to add this as an option. But I don't
see a patch in the queue. Am I missing it? Was I supposed to write it?
--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com
| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Josh Berkus <josh(at)agliodbs(dot)com> |
| Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: What happened to open_sync_without_odirect? |
| Date: | 2011-01-16 00:30:20 |
| Message-ID: | 201101160030.p0G0UKc15365@momjian.us |
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| Lists: | pgsql-hackers |
Josh Berkus wrote:
> Last I remember, we were going to add this as an option. But I don't
> see a patch in the queue. Am I missing it? Was I supposed to write it?
I don't know, but let me add that I am confused how this would look to
users. In many cases, kernels don't even support O_DIRECT, so what
would we do to specify this? What about just auto-disabling O_DIRECT if
the filesystem does not support it; maybe issue a log message about it.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +
| From: | Josh Berkus <josh(at)agliodbs(dot)com> |
|---|---|
| To: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: What happened to open_sync_without_odirect? |
| Date: | 2011-01-16 20:12:11 |
| Message-ID: | 4D33511B.6020607@agliodbs.com |
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| Lists: | pgsql-hackers |
On 1/15/11 4:30 PM, Bruce Momjian wrote:
> Josh Berkus wrote:
>> Last I remember, we were going to add this as an option. But I don't
>> see a patch in the queue. Am I missing it? Was I supposed to write it?
>
> I don't know, but let me add that I am confused how this would look to
> users. In many cases, kernels don't even support O_DIRECT, so what
> would we do to specify this? What about just auto-disabling O_DIRECT if
> the filesystem does not support it; maybe issue a log message about it.
Yes, you *are* confused. The problem isn't auto-disabling, we already
do that. The problem is *auto-enabling*; ages ago we made the
assumption that if o_sync was supported, so was o_direct. We've now
found out that's not true on all platforms.
Also, test results show that even when supported, o_direct isn't
necessarily a win. Hence, the additional fsync_method options.
--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com
| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Josh Berkus <josh(at)agliodbs(dot)com> |
| Cc: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: What happened to open_sync_without_odirect? |
| Date: | 2011-01-17 18:07:42 |
| Message-ID: | 201101171807.p0HI7gd21172@momjian.us |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Lists: | pgsql-hackers |
Josh Berkus wrote:
> On 1/15/11 4:30 PM, Bruce Momjian wrote:
> > Josh Berkus wrote:
> >> Last I remember, we were going to add this as an option. But I don't
> >> see a patch in the queue. Am I missing it? Was I supposed to write it?
> >
> > I don't know, but let me add that I am confused how this would look to
> > users. In many cases, kernels don't even support O_DIRECT, so what
> > would we do to specify this? What about just auto-disabling O_DIRECT if
> > the filesystem does not support it; maybe issue a log message about it.
>
> Yes, you *are* confused. The problem isn't auto-disabling, we already
> do that. The problem is *auto-enabling*; ages ago we made the
> assumption that if o_sync was supported, so was o_direct. We've now
> found out that's not true on all platforms.
>
> Also, test results show that even when supported, o_direct isn't
> necessarily a win. Hence, the additional fsync_method options.
I think it would be clear if we did not use o_direct for open_*sync, but
only for open_*sync_direct, so there was no auto-direct anything --- you
had to ask for it, and if we don't support it, you get an error. Right
now people aren't sure what they are getting.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +