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Re: NetBSD on a database server - WAPBL, softdeps
"Steven M. Bellovin" <smb%cs.columbia.edu@localhost> wrote:
> The issue Thor is pointing out is the granularity of recovery. WAPBL
> and fsck use file-level granularity -- they ensure the consistency of
> the *file system*. Databases have their own, complex internal
> structure; WAPBL and fsck know nothing of them. If you want
> consistency, you have to ensure that the important blocks are written
> out in the proper order. It's reasonable to want the database to do
> that; it is not reasonable to expect the system to.
Yes, for example, PostgreSQL has WAL. Theoretically, database transaction
log does not need an additional file-system journal. However, my point
was not about the consistency - it was about recovery time.
> I think the system call you should be concerned about is
> fsync_range(). Is that used (properly) by your database? Is it fast
No, AFAIK databases use fsync() (maybe DB2 uses fsync_range?), although
it depends at some level. You can change WAL sync method in PostgreSQL,
as well as tune data/commit synchronisation behaviour in most databases.
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