Re: Drawbacks of Berkeley DB cache settings?

[Quanah Gibson-Mount <quanah@stanford.edu>]

--On Thursday, June 26, 2003 2:02 PM +0200 Chris van der Merwe 
<chris@arnes.si> wrote:

> I'm wondering if anyone on the list is familiar with the "inner-workings"
> of the BDB, specifically my question is: Does enlarging the cache of the
> BDB via DB_CONFIG pose any danger of updates to the directory being lost
> in the event of a powerfailure or crash? I ask because I've managed to
> greatly improve the results from OpenLDAP by making some fairly large
> cache settings and I'm wondering if BDB has some mechanism to prevent
> corruption in the event of a crash (with a large un-processed write
> buffer).

Chris,

My understanding of BDB is that when new changes come in, they are written 
to the __db.* files.  When slapd is stopped, or when the time/size of 
changes limit set in slapd.conf by the "checkpoint" attribute are hit, it 
will write any pending changes to the *.bdb files.  After any crash, I 
recommend running db_recover.  If there has been corruption problems caused 
by the crash, BDB will try to fix it.

As always, doing routine backups, and having a method of tracking changes 
is good.  We have an event system here, so if we ever have to do a Point in 
Time restore, we can simply play back all the events from the time the 
backup image was created.  So far, I've seen very few cases where I had an 
unrecoverable DB.  Once was when the partition of the HD got corrupted, and 
the other times were self-inflicted.

--Quanah

--
Quanah Gibson-Mount
Senior Systems Administrator
ITSS/TSS/Computing Systems
Stanford University
GnuPG Public Key: http://www.stanford.edu/~quanah/pgp.html