> > > > No, I am not seeing reloads. Ah, good.
> > I am trying to understand the interactions > > between hard commit, soft commit, transaction log update with a TLOG > > cluster for both leader and follower replicas. For example, after getting > > new segments from the leader the follower replica will still apply the > > hard/soft commit? > Think about the hard commit as a flush of the latest updates to a segment plus checkpoint pointing to all the current valid segments. That checkpoint is also a file. The soft commit is similar to the hard commit in the sense that it creates a segment and a pointer to the valid segments, however, those segments may not be flushed to disk yet, and the checkpoint is not on a file. *In addition* to creating segments, the commits in Solr create searchers to get the latest view of the index (hard-commits only when openSearcher=true and soft-commits always), but that doesn't really matter in the context of replication. The follower replica (a TLOG/PULL) will ask the leader for the last hard commit and replicate all the segments and the file indicating the commit. All the TLOG/PULL replica does after it replicates is open a searcher with all the segments in that checkpoint. Two important notes here: 1) the follower replica doesn't "perform" a commit, it copied it from the leader and 2) this "open a searcher" is not a soft/hard commit, is just opening a searcher (a "commit" usually involves creating segments). * If in the leader (a TLOG replica) you do a soft commit, it'll never make it to the follower, because the follower only replicates the latest hard commit (see ReplicationHandler.indexCommitPoint). * If in the follower (a TLOG replica) you do a soft commit, it won't do any difference, because in the TLOG case, documents are not added to the index (only to the transaction log). (See UpdateCommand.IGNORE_INDEXWRITER flag) * If in the follower (a PULL replica) you do a soft commit, it also wouldn't do any difference, because it doesn't receive the documents anyway (only replicates). Commit is skipped anyway (see DistributedUpdateProcessor.processCommit) The transaction log is only used for recovery purposes (or realtime get). I hope that clarifies things. > > > PS: congratulations on the Berlin Buzzwords' talk. :) > Thanks! > > > > Thanks! > > > > On Mon, Dec 10, 2018 at 9:24 PM Tomás Fernández Löbbe > > <tomasflo...@gmail.com> > > wrote: > > > > > I think this is a good point. The tricky part is that if TLOG replicas > > > don't replicate often, their transaction logs will get too big too, so > you > > > want the replication interval of TLOG replicas to be tied to the > > > auto(hard)Commit interval (by default at least). If you are using them > for > > > search, you may also not want to open a searcher for each fetch... for > PULL > > > replicas, maybe the best way is to use the autoSoftCommit interval to > > > define the polling interval. That said, I'm not sure using different > > > configurations is a good idea, some people may be mixing TLOG and PULL > > and > > > querying them both alike. > > > > > > In the meantime, if you have different hosts for TLOG and PULL > replicas, > > > one workaround you can have is to define the autoCommit time with a > > system > > > property, and use different properties for TLOGs vs PULL nodes. > > > > > > > There is no commit on TLOG/PULL follower replicas, only on the > leader. > > > > Followers fetch the segments and **reload the core** every 150 > seconds > > > > > > Edward, "reload" shouldn't really happen in regular TLOG/PULL fetches. > Are > > > you seeing reloads? > > > > > > On Mon, Dec 10, 2018 at 4:41 PM Erick Erickson < > erickerick...@gmail.com> > > > wrote: > > > > > > > bq. but not every poll attempt they fetch new segment from the leader > > > > > > > > Ah, right. Ignore my comment. Commit will only occur on the followers > > > > when there are new segments to pull down, so your'e right, roughly > > > > every second poll would commit find things to bring down and open a > > > > new searcher......... > > > > On Sun, Dec 9, 2018 at 4:14 PM Edward Ribeiro > > <edward.ribe...@gmail.com> > > > > wrote: > > > > > > > > > > Hi Vadim, > > > > > > > > > > There is no commit on TLOG/PULL follower replicas, only on the > leader. > > > > > Followers fetch the segments and **reload the core** every 150 > seconds > > > > (if > > > > > there were new segments, I suppose). Yeah, followers don't pay the > CPU > > > > > price of indexing, but there are still cache invalidation, > autowarming, > > > > > etc, in addition to network and IO demand. Is that ritht, Erick? > > > > > > > > > > Besides that, Erick is pointing out that under a heavy indexing > > > workload > > > > > you could either have: > > > > > > > > > > 1. Very large transaction logs; > > > > > > > > > > 2. Very large numbers of segments. If that is the case, you could > have > > > > the > > > > > following scenario numerous times: > > > > > 2.1. follower replica downloads segment A and B from leader; > > > > > 2.2 leader merges segments A + B into C; > > > > > 2.3. follower replicas discard A and B and download C on next > poll; > > > > > > > > > > Under the second condition followers needlessly downloaded segments > > > that > > > > > would eventually be merged. > > > > > > > > > > IMO, you should carefully evaluate if the use of TLOG/PULL is > really > > > > > recommended for your cluster setup, plus indexing and querying > > > workload. > > > > > You can very much stay with a NRT setup if it suits you better. The > > > > videos > > > > > below provide a nice set of hints for when to choose between NRT or > > > some > > > > > combination of TLOG and PULL. > > > > > > > > > > https://youtu.be/XIb8X3MwVKc > > > > > > > > > > https://youtu.be/dkWy2ykzAv0 > > > > > > > > > > https://youtu.be/XqfTjd9KDWU > > > > > > > > > > Regards, > > > > > Edward > > > > > > > > > > Em dom, 9 de dez de 2018 16:56, <vadim.iva...@spb.ntk-intourist.ru > > > > escreveu: > > > > > > > > > > > > > > > > > If hard commit max time is 300 sec then commit happens every 300 > > sec > > > > on > > > > > > tlog leader. And new segments pop up on the leader every 300 sec, > > > > during > > > > > > indexing. Polling interval on other replicas 150 sec, but not > every > > > > poll > > > > > > attempt they fetch new segment from the leader, afaiu. Erick, do > you > > > > mean > > > > > > that on all other tlog replicas(not leaders) commit occurs every > > > poll? > > > > > > воскресенье, 09 декабря 2018г., 19:21 +03:00 от Erick Erickson > > > > > > erickerick...@gmail.com : > > > > > > > > > > > > >Not quite, 600000. The polling interval is half the commit > > > > interval.... > > > > > > > > > > > > > >This has always bothered me a little bit, I wonder at the > utility > > > of a > > > > > > >config param. We already have old-style replication with a > > > > > > >configurable polling interval. Under very heavy indexing loads, > it > > > > > > >seems to me that either the tlogs will grow quite large or > we'll be > > > > > > >pulling a lot of unnecessary segments across the wire, segments > > > > > > >that'll soon be merged away and the merged segment re-pulled. > > > > > > > > > > > > > >Apparently, though, nobody's seen this "in the wild", so it's > > > > > > >theoretical at this point. > > > > > > >On Sun, Dec 9, 2018 at 1:48 AM Vadim Ivanov > > > > > > < vadim.iva...@spb.ntk-intourist.ru> wrote: > > > > > > > > > > > > > > Thanks, Edward, for clues. > > > > > > > What bothers me is newSearcher start, warming, cache clear... > all > > > > that > > > > > > CPU consuming stuff in my heavy-indexing scenario. > > > > > > > With NRT I had autoSoftCommit: 300000 . > > > > > > > So I had new Searcher no more than every 5 min on every > replica. > > > > > > > To have more or less the same effect with TLOG - PULL > collection, > > > > > > > I suppose, I have to have : 300000 > > > > > > > (yes, I understand that newSearchers start asynchronously on > leader > > > > and > > > > > > replicas) > > > > > > > Am I right? > > > > > > > -- > > > > > > > Vadim > > > > > > > > > > > > > > > > > > > > >> -----Original Message----- > > > > > > >> From: Edward Ribeiro [mailto:edward.ribe...@gmail.com] > > > > > > >> Sent: Sunday, December 09, 2018 12:42 AM > > > > > > >> To: solr-user@lucene.apache.org > > > > > > >> Subject: Re: Soft commit and new replica types > > > > > > >> > > > > > > >> Some insights in the new replica types below: > > > > > > >> > > > > > > >> On Sat, December 8, 2018 08:42, Vadim Ivanov < > > > > > > >> vadim.iva...@spb.ntk-intourist.ru wrote: > > > > > > >> > > > > > > >>> > > > > > > >>> From Ref guide we have: > > > > > > >>> " NRT is the only type of replica that supports > soft-commits..." > > > > > > >>> "If TLOG replica does become a leader, it will behave the > same as > > > > if it > > > > > > >>> was a NRT type of replica." > > > > > > >>> Does it mean, that if we do not have NRT replicas in the > cluster > > > > then > > > > > > >>> autoSoftCommit section in solconfig.xml Ignored completely > (even > > > on > > > > > > TLOG > > > > > > >>> leader)? > > > > > > >>> > > > > > > >> > > > > > > >> No, not completely. Both TLOG and PULL nodes will periodically > > > poll > > > > the > > > > > > >> leader for changes in index segments' files and download those > > > > segments > > > > > > >> from the leader. If hard commit max time is defined in > > > > solrconfig.xml > > > > > > the > > > > > > >> polling interval of each replica will be half that value. Or > else > > > > if the > > > > > > >> soft commit max time is defined then the replicas will use > half > > > the > > > > soft > > > > > > >> commit max time as the interval. If neither are defined then > the > > > > poll > > > > > > >> interval will be 3 seconds (hard coded). See here: > > > > > > >> https://github.com/apache/lucene- > > > > > > >> > > > > > > solr/blob/75b183196798232aa6f2dcaaaab117f309119053/solr/core/src/java/o > > > > > > >> rg/apache/solr/cloud/ReplicateFromLeader.java#L68-L77 > > > > > > >> > > > > > > >> If the TLOG is the leader it will index locally and append > the doc > > > > to > > > > > > >> transaction log as a NRT node would do as well as it will > > > > synchronously > > > > > > >> replicate the data to other TLOG replicas' transaction logs > (PULL > > > > nodes > > > > > > >> don't have transaction logs). But TLOG/PULL replicas doesn't > > > support > > > > > > soft > > > > > > >> commits nor real time gets, afaik. > > > > > > >> > > > > > > >>> > > > > > > >> > > > > > > >>> > > > > > > >>> 60000 > > > > > > >>> > > > > > > >>> > > > > > > >>> Should we say that in autoCommit section openSearcher is > always > > > > true in > > > > > > >>> that case? > > > > > > >> > > > > > > >> > > > > > > >> > > > > > > >> 10000 > > > > > > >> 30000 > > > > > > >> 512m > > > > > > >> false > > > > > > >> > > > > > > >> > > > > > > >> Does it mean that new Searcher always starts on all replicas > when > > > > hard > > > > > > >> commit happens on leader? > > > > > > >> > > > > > > >> > > > > > > >> Nope. Or at least, the searcher is not synchronously created. > Each > > > > non > > > > > > >> leader replica will periodically fetch the index changes from > the > > > > leader > > > > > > >> and open a new searcher to reflect those changes as seen here: > > > > > > >> https://github.com/apache/lucene- > > > > > > >> > > > > > > solr/blob/75b183196798232aa6f2dcaaaab117f309119053/solr/core/src/java/o > > > > > > >> rg/apache/solr/handler/IndexFetcher.java#L653 > > > > > > >> But it's important to note that the potential delay between > the > > > > leader's > > > > > > >> hard commit and the other replicas fetching those changes > from the > > > > > > leader > > > > > > >> and opening a new searcher to reflect latest changes. > > > > > > >> > > > > > > >> PS: I am still digging these new replica types so I can have > > > > > > misunderstood > > > > > > >> or missed some aspect of it. > > > > > > >> > > > > > > >> Regards, > > > > > > >> Edward > > > > > > > > > > > > > > > > > > > > > >
