Re: fsync vs open_sync (more info)

> On Tue, 2004-08-10 at 07:48, pgsql@mohawksoft.com wrote:
>> Some more information:
>>
>> I started to perform the tests on one of the machines in my lab, and
>> guess
>> what, almost no difference between fsync and open_sync. Either on jfs or
>> ext2.
>>
>> The difference, Linux 2.6.3? My original tests where on Linux 2.4.25.
> Very hazy memory recalls something about O_SYNC not really doing
> anything in early kernel versions.
>
>>
>> The good part is that open_sync wasn't worse.

In early Linux kernels, O_SYNC was implemented using fsync(), and there
was an amount of debate about people using "O_SYNC" should see performance
degradation.

>>
>> Just a question about conceptually, "What is the right thing to do?" I
>> started to think about this. To me, the O_SYNC flag is to ensure that
>> what
>> you write, at the time of write, is on the disk. In SQL terms it is like
>> "auto commit." Calling fsync or fdatasync is so that one can batch write
>> calls and flush it out to disk in one shot, conceptually, it is like
>> transaction.
> With the caveat that the kernel can start flushing your data to disk
> in the background, not just when you call fdatasync/fsync.

I was speaking in conceptual terms, not exact ones. Just a general analogy.

In theory, theory and practice are the same thing, in practice, they are not.