On 2017-06-22 12:43:16 -0400, Robert Haas wrote:
> On Wed, Jan 25, 2017 at 2:52 PM, Andres Freund wrote:
> > You'll, depending on your workload, still have a lot of lseeks even if
> > we were to use pread/pwrite because we do lseek(SEEK_END) to get file
> > sizes.
>
> I'm
On Wed, Jan 25, 2017 at 2:52 PM, Andres Freund wrote:
> You'll, depending on your workload, still have a lot of lseeks even if
> we were to use pread/pwrite because we do lseek(SEEK_END) to get file
> sizes.
I'm pretty convinced that the lseek overhead that we're incurring
Hi,
Synthetic PG workload or real world production workload?
Both might work, production-like has bigger pull, but I'd guess
synthetic is good enough.
Thanks! The box should get PostgreSQL in the not too distant future.
It'll get a backup from prod, but will act as new prod, so it might
Hi,
On 2017-01-25 10:16:32 +0100, Tobias Oberstein wrote:
> > > Using pread instead of lseek+read halfes the syscalls.
> > >
> > > I really don't understand what you are fighting here ..
> >
> > Sure, there's some overhead. And as I said upthread, I'm much less
> > against this change than Tom.
Hi Andres,
Using pread instead of lseek+read halfes the syscalls.
I really don't understand what you are fighting here ..
Sure, there's some overhead. And as I said upthread, I'm much less
against this change than Tom. What I'm saying is that your benchmarks
haven't shown a benefit in a
Hi Alvaro,
Am 24.01.2017 um 19:36 schrieb Alvaro Herrera:
Tobias Oberstein wrote:
I am benchmarking IOPS, and while doing so, it becomes apparent that at
these scales it does matter _how_ IO is done.
The most efficient way is libaio. I get 9.7 million/sec IOPS with low CPU
load. Using any
On 2017-01-24 19:25:52 +0100, Tobias Oberstein wrote:
> Hi,
>
> > > pid |syscall| cnt | cnt_per_sec
> > > -+---+-+-
> > > | syscalls:sys_enter_lseek | 4091584 | 136386
> > >
On 2017-01-24 15:36:13 -0300, Alvaro Herrera wrote:
> Tobias Oberstein wrote:
>
> > I am benchmarking IOPS, and while doing so, it becomes apparent that at
> > these scales it does matter _how_ IO is done.
> >
> > The most efficient way is libaio. I get 9.7 million/sec IOPS with low CPU
> >
Tobias Oberstein wrote:
> I am benchmarking IOPS, and while doing so, it becomes apparent that at
> these scales it does matter _how_ IO is done.
>
> The most efficient way is libaio. I get 9.7 million/sec IOPS with low CPU
> load. Using any synchronous IO engine is slower and produces higher
Hi,
pid |syscall| cnt | cnt_per_sec
-+---+-+-
| syscalls:sys_enter_lseek | 4091584 | 136386
| syscalls:sys_enter_newfstat | 2054988 | 68500
|
Hi,
On 2017-01-24 18:57:47 +0100, Tobias Oberstein wrote:
> Am 24.01.2017 um 18:41 schrieb Andres Freund:
> > On 2017-01-24 18:37:14 +0100, Tobias Oberstein wrote:
> > > The syscall overhead is visible in production too .. I watched PG using
> > > perf
> > > live, and lseeks regularily appear at
Hi,
Am 24.01.2017 um 18:41 schrieb Andres Freund:
Hi,
On 2017-01-24 18:37:14 +0100, Tobias Oberstein wrote:
assume that it'd get more than swamped with doing actualy work, and with
buffering the frequently accessed stuff in memory.
What I am trying to say is: the syscall overhead of doing
Hi,
On 2017-01-24 18:37:14 +0100, Tobias Oberstein wrote:
> > assume that it'd get more than swamped with doing actualy work, and with
> > buffering the frequently accessed stuff in memory.
> >
> >
> > > What I am trying to say is: the syscall overhead of doing lseek/read/write
> > > instead of
Hi,
Switching to sync engine, it drops to 9.1 mio - but the system load then is
also much higher!
I doubt those have very much to do with postgres - I'd quite strongly
In the machine in production, we see 8kB reads in the 300k-650k/s range.
In spikes, because, yes, due to the 3TB RAM, we
Hi,
On 2017-01-24 18:11:09 +0100, Tobias Oberstein wrote:
> I have done lots of benchmarking over the last days on a massive box, and I
> can provide numbers that I think show that the impact can be significant.
> Above number was using psync FIO engine .. with libaio, it's at 9.7 mio with
>
Hi guys,
pls bare with me, this is my first post here. Pls also excuse the length
.. I was trying to do all my homework before posting here;)
The overhead of lseek/read/write vs pread/pwrite (or even
pvread/pvwrite) was previously discussed here
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