Andy, Rob, thanks for your explanations and suggestions - now I understand the issue much better.
I tried different approaches to solve it but the freeze keeps occurring when the leading Zookeper instance is down/stopped permanently. (BTW: shutting down even 2 out of 3 RDF Delta servers does not have any negative impact on the SPARQL execution which is great). Andy, to answer your question about when the freeze happens: For SELECTs it always occurs between the second and third (last) log entry: [2020-09-10 05:52:13] Fuseki INFO [13] POST http://localhost:3031/ds [2020-09-10 05:52:13] Fuseki INFO [13] Query = SELECT * {?s ?p ?o} [2020-09-10 05:52:23] Fuseki INFO [13] 200 OK (10.023 s) For INSERTs log looks like this: [2020-09-10 05:48:50] Fuseki INFO [7] POST http://localhost:3031/ds [2020-09-10 05:49:00] HTTP INFO Send patch id:758bcf (165 bytes) -> ds:090688 [2020-09-10 05:49:09] Fuseki INFO [7] 200 OK (19.059 s) [2020-09-10 05:50:15] Fuseki INFO [10] POST http://localhost:3031/ds [2020-09-10 05:50:25] HTTP INFO Send patch id:472bf1 (165 bytes) -> ds:090688 [2020-09-10 05:50:44] Fuseki INFO [10] 200 OK (29.042 s) Thanks, Piotr wt., 18 sie 2020 o 22:03 Andy Seaborne <a...@apache.org> napisał(a): > Piotr, > > It will depend on how long zookeeper takes to resync. One of the factors > is how big the zookeeper database has become because when a ZK server > starts, it has to process the snapshot and any logs to > > But while syncing the other zk server should still provide service > (read-only) - maybe the Fuseki server is choosing the fresh zk server so > it'll wait whereas as if went to another server, it would be OK (for a > read-transaction). I thought the new one would not service request until > ready but I'm not sure. > > At what point in the Fuseki log file does the freeze happen? After the > HTTP request is received or as it exits (is the freeze before or after > the middle log line of the three for a request). > > With 3 zk servers, the system can survive one outage. > With 5 zk server it can survive one outage and still allow write, or 2 > out and read-only. > > You can also configure zk in more complex primary-secondary configurations. > > A load balancer between the Fuseki servers and the zk servers may help. > > Andy > > > On 17/08/2020 17:09, Piotr Nowara wrote: > > Hi, > > > > We are testing RDF Delta with three Zookeeper instances. Sometimes when > we > > kill one of those Zookeper instances Fuseki freezes for about 30 seconds > > which is bad. Is this expected? Will increasing the number of Zookeper > > instances help to avoid such issues? > > Yes and no. > > > > > Thanks, > > Piotr Nowara > > >
