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Re: Checkpointing and BDB
On Friday, Apr 25, 2003, at 08:31 US/Pacific, Quanah Gibson-Mount wrote:
So I have a basic question as to the usefulness of checkpointing. The
stated purpose of checkpointing is to make sure that received writes
are flushed to disk. How does this help you if slapd crashes between
writes? At Stanford, we have about 14,500 changes a day.
If there is one feature I appreciated about Netscape, it was that it
knew what updates the slaves had or had not received. Therefore, to
recover a slave, all you had to do was load in a DB dump from a
previous time, and that slave would be caught up by the master. That
does not appear possible with OpenLDAP. The only thing I can see to
guarantee consistency with OpenLDAP when slapd dies on a slave is to
export the database on the master, copy it to the slave, and then copy
it in. Which makes checkpointing once again worthless. I suppose it
could be helpful for the master, in that you know you only have to go
back say 10 minutes in time of your changes if the master crashes, to
make sure it has received everything.
Is there a more elegant solution I'm missing here?
Seems more like a replication issue. I've had good luck with telling
slapd to generate replog entries for fake servers that slurpd will
ignore, so that the changes remain in the replog and then using the
preserved changes to replay things later.
Slurpd isn't designed for that manner of abuse though, so it tends to
hold the changes in memory until you halt slurpd and rotate replication
logs. Automated rotation of that requires you examine timestamps of
the replication entries wrt the slurpd status file.
The nice thing is then you Have all the changes for whatever span of
time you want, and can do exactly what you need. Also handy for
Ultimately this is probably the wrong direction, but has the virtue of