Am 06.07.2011 09:14, schrieb Sascha Wildner:
On Sun, 03 Jul 2011 09:12:43 +0200, Steve O'Hara-Smith
<[email protected]> wrote:
On Sat, 2 Jul 2011 23:40:53 -0700 (PDT)
Matthew Dillon <[email protected]> wrote:
I'll continue to think about how at least a small number of hardlinks
could be implemented without turning already complex cluster
algorithms into a disaster zone. So far I'm drawing a blank.
There are plenty of filesystems that support hard links around, but
hardly any that support multi-master clustering. I would say that hard
links are a small price to pay for multi-master clustering.
The question is too how many users will use the multi-master feature vs.
how many users will be using it as a generic file system on their single
machine. Don't know what the answer is to that one, though.
The issue with hard links is that they are part of POSIX and stuff out
in the wild will just use it and expect it to work like on most of the
other file systems.
We've already had a case where stuff (gdb it was I think) would
configure wrongly because hammer would not update file access times on
read (which is specified in POSIX too). If there are issues with the
hard links missing, I guess they would be along the same lines.
But I have no idea how big a problem it will be in practice.
A conversation on #postgresql made me come back to this thread. E.g.
PostgreSQL is a software that 100% depends on hardlinks, according to this:
17:35 < hlan> the file system I use for my postgres data storage does
not support hard links... and it just blew up with "LOG: could not link
file
"pg_xlog/xlogtemp.11066" to
"pg_xlog/000000010000000000000001" (initialization of log file 0,
segment 1): Function not implemented"
17:36 < hlan> why would you rely on hard links? seriously... :/
17:36 < hlan> are there some way to disable this behavior?
17:42 < mst> hlan: because hard links are widely available and atomic
17:42 < mst> hlan: I suggest you ask your sysadmin for a working file system
17:49 < mastermind> hlan: what kind of strange filesystem do you have there?
17:49 < hlan> mst: I wrote the file system and I am the sysadmin. I
didn't want to support hard links because they are obscure/hardly used
and easily
creates confusion due to them being non transparent...
and why use them when there are symlinks?
17:49 < hlan> postgres is the first software I actually had problems with
17:50 < mst> hlan: they're not obscure, they're heavily used
17:50 < mst> hlan: atomic 'mv' is impossible without them
17:50 < mst> hlan: if you don't have that, a massive percentage of *n?x
standard approaches are impossible
17:50 < hlan> I guess I have to implement hard links then
Jan
