From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Greg Smith <greg(at)2ndquadrant(dot)com>, Jon Nelson <jnelson+pgsql(at)jamponi(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: fallocate / posix_fallocate for new WAL file creation (etc...) |
Date: | 2013-05-30 12:28:20 |
Message-ID: | 20130530122820.GB14029@awork2.anarazel.de |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On 2013-05-30 08:17:28 -0400, Peter Eisentraut wrote:
> On 5/30/13 7:13 AM, Andres Freund wrote:
> > Why? The spec doesn't specify that case and that very well allows other
> > behaviour. Glibc sure does behave sensibly and zeroes the data
> > (sysdeps/posix/posix_fallocate64.c for the generic implementation) and
> > so does linux' fallocate() syscall, but that doesn't say much about
> > other implementations.
>
> glibc actually only writes one byte to every file system block, to make
> sure the block is allocated. It doesn't actually zero every byte.
Which is fine since that guarantees we can read from those areas... And
unless I misremember something that actually guarantees that the rest of
the data is initialized to zero as well. Yes: "subsequent reads of data
in the gap shall return bytes with the value 0 until data is actually
written into the gap".
But really, I am not at all concerned about some obscure values being
returned, but about a read() not being successful..
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
From | Date | Subject | |
---|---|---|---|
Next Message | Stefan Kaltenbrunner | 2013-05-30 12:32:46 | Re: PostgreSQL 9.3 beta breaks some extensions "make install" |
Previous Message | Andres Freund | 2013-05-30 12:20:53 | Re: fallocate / posix_fallocate for new WAL file creation (etc...) |