On Thu, 10 Mar 2011, Henry Chang wrote:
> Hi,
>
> Another question is about PG::do_peer. I wonder if we should modify
> the condition of inferring no missing as follows:
>
> diff --git a/src/osd/PG.cc b/src/osd/PG.cc
> index e634296..4ce3336 100644
> --- a/src/osd/PG.cc
> +++ b/src/osd/PG.cc
> @@ -1632,7 +1632,7 @@ void PG::do_peer(ObjectStore::Transaction& t,
> list<Context*>& tfin,
> if (pi.is_empty())
> continue;
> if (peer_missing.find(peer) == peer_missing.end()) {
> - if (pi.last_update == pi.last_complete) {
> + if (pi.last_update == pi.last_complete && pi.last_update >= log.tail) {
> dout(10) << " infering no missing (last_update==last_complete)
> for osd" << peer << dendl;
> peer_missing[peer].num_missing(); // just create the entry.
> search_for_missing(peer_info[peer], &peer_missing[peer], peer);
>
> If pi.last_update < log.tail, we cannot know if the peer has any
> missing. Shouldn't we try to pull the peer's missing+backlog first
> before inferring no missing and go ahead activating the pg?
Yeah, this is definitely broken, but I think it's broken even beyond that
specific case. It looks like it's just an ill-conceived optimization.
The problem is that peer_missing needs to have missing in terms of the
master log (on the primary), not the peer's log, and in order to
calculate that we need pull the log+missing. (In the
last_update==last_complete case I was trying to optimize, the missing set
will just be empty.) The current code missing the case where the replica
has a divergent log or and older last_update (even one > log.tail).
I think this shortcut _only_ makes sense when the replica is perfectly up
to date, i.e.
if (pi.last_update == pi.last_complete &&
pi.last_update == info.last_update) {
Does that sound right?
> Sorry for separating my questions into multiple emails.
No problem, it's easier that way. :)
Thanks!
sage
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