[19749] in Kerberos_V5_Development
Re: LMDB KDB module design notes
daemon@ATHENA.MIT.EDU (Simo Sorce)
Thu Apr 12 11:57:10 2018
Message-ID: <1523548612.10955.52.camel@redhat.com>
From: Simo Sorce <simo@redhat.com>
To: Greg Hudson <ghudson@mit.edu>, krbdev@mit.edu
Date: Thu, 12 Apr 2018 11:56:52 -0400
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On Thu, 2018-04-12 at 10:59 -0400, Greg Hudson wrote:
> On 04/12/2018 08:03 AM, Simo Sorce wrote:
> > > The lockout environment is never emptied, never iterated over, and
> > > uses only short-lived transactions, so the KDC is never blocked more
> > > than briefly.
> >
> > I am not a fan of setups that use multiple files for databases, especially when
> > transactions need to span multiple ones.
> > What is the underlying reason to do this in the new design instead of using a
> > single database file with all the data ?
>
> Transactions are per-environment, so if we use one database file and a
> write transaction for loads, loads would block the KDC. That's worse
> than what we have with DB2.
>
> Alternatively we could load into a temporary database file and rename it
> into place like we do with DB2. But we would then have to close and
> reopen the database between operations like we do with DB2, or somehow
> signal processes that have the database open to reopen it after a load
> completes.
How common are loads ?
As far as I know LMDB will let you keep reading during a transaction, so
the KDC would block only if there are write operations, but won't block
in general, right ?
The only write operations are on AS requests, when lockout are enabled
and when that triggers a change in the lockout fields. How common is that ?
Would that something that can be mitigated by deferring those writes during
transactions ?
Simo.
--
Simo Sorce
Sr. Principal Software Engineer
Red Hat, Inc
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