Re: Improve lseek scalability v3

2011/9/19 Matthew Wilcox <matthew(at)wil(dot)cx>:
> On Mon, Sep 19, 2011 at 08:31:00AM -0400, Stephen Frost wrote:
>> * Benjamin LaHaise (bcrl(at)kvack(dot)org) wrote:
>> > For such tables, can't Postgres track the size of the file internally?  I'm
>> > assuming it's keeping file descriptors open on the tables it manages, in
>> > which case when it writes to a file to extend it, the internally stored size
>> > could be updated.  Not making a syscall at all would scale far better than
>> > even a modified lseek() will perform.
>>
>> We'd have to have it in shared memory and have a lock around it, it
>> wouldn't be cheap at all.
>
> Yep, that makes perfect sense.  After all, the kernel does basically the
> same thing to maintain this information; why should we have userspace
> duplicating the same infrastructure?
>
> I must admit, I'd never heard of this usage of lseek to get the current
> size of a file before; I'd assumed everybody used fstat.  Given this
> legitimate reason for a high-frequency calling of lseek, I withdraw my
> earlier objection to the patch series.
>
> --
> Matthew Wilcox                          Intel Open Source Technology Centre
> "Bill, look, we understand that you're interested in selling us this
> operating system, but compare it to ours.  We can't possibly take such
> a retrograde step."
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I really don't understand the approach here. An improvement is an
improvement, do we need a use case to add an improvement to the
kernel? We are not talking about to add a new syscall or to do an ABI
change in this case. So my absolute ack to these patches.

Marco