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<div class="moz-cite-prefix">On 10/17/2013 10:49 AM, Ludwig Krispenz
wrote:<br>
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<div class="moz-cite-prefix">On 10/17/2013 10:15 AM, thierry
bordaz wrote:<br>
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<div class="moz-cite-prefix">On 10/16/2013 05:41 PM, Ludwig
Krispenz wrote:<br>
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<div class="moz-cite-prefix">On 10/16/2013 05:28 PM, Mark
Reynolds wrote:<br>
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<div class="moz-cite-prefix">On 10/16/2013 11:05 AM, Ludwig
Krispenz wrote:<br>
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<div class="moz-cite-prefix">On 10/15/2013 10:41 PM, Mark
Reynolds wrote:<br>
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<div class="moz-text-flowed" style="font-family:
-moz-fixed; font-size: 12px;" lang="x-western"><a
moz-do-not-send="true" class="moz-txt-link-freetext"
href="https://fedorahosted.org/389/ticket/47368">https://fedorahosted.org/389/ticket/47368</a>
<br>
<br>
So we run into issues when trying to figure out if
replicas are in synch(if those replicas use fractional
replication and "strip mods"). What happens is that
an update is made on master A, but due to fractional
replication there is no update made to any replicas.
So if you look at the ruv in the tombstone entry on
each server, it would appear they are out of synch.
So using the ruv in the db tombstone is no longer
accurate when using fractional replication. <br>
<br>
I'm proposing a new ruv to be stored in the backend
replica entry: e.g.
cn=replica,cn="dc=example,dc=com",cn=mapping
tree,cn=config. I'm calling this the "replicated
ruv". So whenever we actually send an update to a
replica, this ruv will get updated. </div>
</blockquote>
I don't see how this will help, you have an additional
info on waht has been replicated (which is available on
the consumer as well) and you have a max csn, but you
don't know if there are outstanding fractional changes to
be sent.<br>
</blockquote>
Well you will know on master A what operations get
replicated(this updates the new ruv before sending any
changes), and you can use this ruv to compare against the
other master B's ruv(in its replication agreement). Maybe
I am missing your point? </blockquote>
MY point is that the question is, what is NOT yet replicated.
Without fractional replication you have states of the ruv on
all servers, and if ruv(A) > ruv(B) you know there are
updates missing on B. With fractional, if (ruv(A) > ruv(B)
this might be ok or not. If you keep an additional ruv on A
when sending updates to be, you can only record what ws sent
or attempted to send, but not what still has to be sent<br>
</blockquote>
<br>
I agree with you Ludwig, but unless I missed something would not
be enough to know that the replica B is late or in sync ?<br>
<br>
For example, we have updates U1 U2 U3 and U4. U3 should be
skipped by fractional replication.<br>
<br>
replica RUV (tombstone) on master_A contains U4 and master_B
replica RUV contains U1.<br>
Let's assume that as initial value of the "replicated ruv" on
master_A we have U1.<br>
Starting a replication session, master_A should send U2 and
update the "replicated ruv" to U2.<br>
If the update is successfully applied on master_B, master_B
replica ruv is U2 and monitoring the two ruv shoud show they are
in sync.<br>
</blockquote>
They are not, since U4 is not yet replicated, in master_A you see
the "normal" ruv as U4 and the "replicated" ruv as U2, but you
don't know how many changes are between U2 and U4 an if any of
them should be replicated, the replicated ruv is more or less a
local copy of the remote ruv<br>
</blockquote>
<br>
Yes I agree they are not this is a transient status. Transient
because the RA will continue going through the changelog until it
hits U4. At this point it will write U4 in the "replicated RUV" and
until master_B will apply U4 both server will appear out of sync.<br>
My understanding is that this "replicated RUV" only says it is in
sync or not, but does not address how far a server is out of sync
from the other (how many updates are missing). When you say it is
more or less a copy, it is exactly what it is. If it is a copy =>
in sync, if it different => out of sync.<br>
<br>
<blockquote cite="mid:525FA4B3.6090209@redhat.com" type="cite">
<blockquote cite="mid:525F9C8A.4060605@redhat.com" type="cite"> If
the update is not applierd, master_B replica ruv stays at U1 and
the two ruv will show out of sync.<br>
<br>
In the first case, we have a transient status of 'in sync'
because the replica agreement will evaluate U3 then U4 then send
U4 and store it into the "replicated ruv". At this point
master_A and master_B will appear out of sync until master_B
will apply U4.<br>
If U4 was to be skipped by fractional we have master_B ruv and
Master_A replicated ruv both showing U2 and that is correct both
servers are in sync.<br>
<br>
Mark instead of storing the replicated ruv in the replica, would
not be possible to store it into the replica agreement (one
replicated ruv per RA). So that it can solve the problem of
different fractional replication policy ?<br>
<br>
<blockquote cite="mid:525EB3AE.2050609@redhat.com" type="cite">
<blockquote cite="mid:525EB0B9.8020901@redhat.com" type="cite">Do
you mean changes that have not been read from the changelog
yet? My plan was to update the new ruv in
perform_operation() - right after all the "stripping" has
been done and there is something to replicate. We need to
have a ruv for replicated operations.<br>
<br>
I guess there are other scenarios I didn't think of, like if
replication is in a backoff state, and valid changes are
coming in. Maybe, we could do test "stripping" earlier in
the replication process(when writing to the changelog?), and
then update the new ruv there instead of waiting until we
try and send the changes.<br>
<blockquote cite="mid:525EAB4D.80308@redhat.com" type="cite">
<blockquote cite="mid:525DA868.6040003@redhat.com"
type="cite">
<div class="moz-text-flowed" style="font-family:
-moz-fixed; font-size: 12px;" lang="x-western">Since
we can not compare this "replicated ruv" to the
replicas tombstone ruv, we can instead compare the
"replicated ruv" to the ruv in the replica's repl
agreement(unless it is a dedicated consumer - here we
might be able to still look at the db tombstone ruv to
determine the status). <br>
<br>
Problems with this approach: <br>
<br>
- All the servers need to have the same replication
configuration(the same fractional replication policy
and attribute stripping) to give accurate results. <br>
<br>
- If one replica has an agreement that does NOT
filter the updates, but has agreements that do filter
updates, then we can not correctly determine its
synchronization state with the fractional replicas. <br>
<br>
- Performance hit from updating another ruv(in
cn=config)? <br>
<br>
<br>
Fractional replication simply breaks our monitoring
process. I'm not sure, not without updating the repl
protocol, that we can cover all deployment
scenarios(mixed fractional repl agmts, etc). However,
I "think" this approach would work for most
deployments(compared to none at the moment). For IPA,
since they don't use consumers, this approach would
work for them. And finally, all of this would have to
be handled by a updated version of repl-monitor.pl. <br>
<br>
This is just my preliminary idea on how to handle
this. Feedback is welcome!! <br>
<br>
Thanks in advance, <br>
Mark <br>
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<pre class="moz-signature" cols="72">--
Mark Reynolds
389 Development Team
Red Hat, Inc
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