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Re: delta-syncrepl problems with 2.4.12

John Morrissey wrote:
On Tue, Nov 11, 2008 at 02:18:10PM -0800, Quanah Gibson-Mount wrote: 
--On Tuesday, November 11, 2008 4:35 PM -0500 John Morrissey
<jwm@horde.net>  wrote:

Instead of slapcat(8)/slapadd(8)ding the old databases, we're removing
the existing databases and allowing slapd(8) to delta-syncrepl a copy
from scratch. Ironing out this use case is especially important for us
since we expect to be adding a number of consumers in the coming months
and would obviously prefer to bring them online without having to shut
down any other slapd instances for slapcat(8)ting.

Why would you have to shut down a server to slapcat it?  Hot slapcatting
has been supported for a long time.


Right, slapcat's man page indicates it's always safe to run against the bdb
backend, but I suspect that's referring more to read concurrency and not
necessarily the generation of a consistent, point-in-time snapshot of the
database.

Empirically, slapcat output does not have a consistent view of the database
while dumping it. Specifically, when slapcat is running and one changes an
entry that hasn't been dumped yet, that change will appear in slapcat's
output. Using slapadd's -w option would definitely be unsafe in this
situation.

The -w option is only meant to be used when your LDIF does not already contain contextCSN values. There's no need to use it otherwise, and as you note, it would be detrimental in this case.

Without the -w option seems safe at first glance since the suffix entry's
contextCSN will be older than any CSN in the generated LDIF. It seems that
any syncrepl updates that have already been "applied" by virtue of the
aforementioned slapcat behavior will simply be skipped since there will be
no changes to the entry? Still, I couldn't find anything in the
Administrator's Guide about this, and it feels like there's some concurrency
case I'm not considering here, so I'd definitely appreciate hearing any
thoughts you have on this.


slapcat/slapadd (no -w), let syncrepl figure out the rest.


We haven't upgraded our provider to 2.4 yet, since we wanted to get some
consumers upgraded first. Would running a 2.4 provider with 2.3 consumers be
OK? The contextCSN format changed to add fractional seconds; will that have
any adverse impact on existing 2.3 consumers that try to continue
syncrepling?


A recent enough 2.3 will accept 2.4-format CSNs.

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