Replicas 2 Full Movie
Marthe Bernskoetter
However the interesting thing is in this case that the two replicas blocking the update were registered to myself and another guy. I had checked both those iPads and neither had a synced version of that map on it. So I don't know why this happened.
I wonder if this solution is easier?
Open the service in AGO. Go to "settings". Disable "Sync". Save. You will get a warning that there are replicas on the server. Ignore this. Enable sync again.
I have only tried this with one "hidden" replica. That worked. But if it works with several, it will be efficient compared to remove manually one by one.
It seems some circumstances can cause dead replicas on the server. I had deleted all my online maps in Collector on all my devices, but when I checked the replicas of the service, I found 4 replicas which stopped me from overwriting my service in AGOL.
Depending on how you remove the offline data from the app will push the replicas off the service. If you manually delete or remove the data from the device this will not tell the app to remove the replicas from your service because if you had just moved the data off of the device due to an issue you will still want the replica on the service to be able to save your data and sync it back.
Let's say in Collector. if I download an offline map to edit, I assume a replica will be created for the feature service. when I delete the offline map using the manage tool provided by Collector, I imagine it will notify the service that the replica is not needed any more, and the server will delete the replica as nobody can use this replica at a later time.
I talked to the team. There is an issue where the replicas will not get unregistered when you remove it from the app if there are multiple services in the map. This is fixed and will be in a Nov update.
Spanner automatically replicates at the byte level. As describedin Life of Spanner Reads and Writes, it takes advantage of thiscapability in the underlying file system that it's built on.Spanner writes database mutations to files in this file system,and the file system takes care of replicating and recovering the files when amachine or disk fails.
Even though the underlying distributed file system that Spanneris built on already provides byte-level replication, Spanner alsoreplicates data to provide the additional benefits of data availability andgeographic locality. At a high level, all data in Spanner isorganized into rows. Spanner creates multiple copies, or"replicas," of these rows, then stores these replicas in different geographicareas. Spanner uses a synchronous, Paxos-based replication scheme,in which voting replicas take a vote on every write requestbefore the write is committed. This property of globally synchronous replicationgives you the ability to read the most up-to-date data from anySpanner read-write or read-only replica.
Spanner creates replicas of each database split. A splitholds a range of contiguous rows, where the rows are ordered by primary key.All of the data in a split is physically stored together in the replica, andSpanner serves each replica out of an independent failurezone. For more information, see About schemas.
A set of splits is stored and replicated using Paxos. Within each Paxosreplica set, one replica is elected to act as the leader. Leader replicasare responsible for handling writes, while any read-write or read-only replicacan serve a read request without communicating with the leader (though if astrong read is requested, the leader will typically be consulted to ensure thatthe read-only replica has received all recent mutations).
Data availability: Having more copies of your data makes the data moreavailable to clients that want to read it. Also, Spanner canstill serve writes even if some of the replicas are unavailable, becauseonly a majority of voting replicas are required in order to commit a write.
Geographic locality: Having the ability to place data across differentregions and continents with Spanner means data can begeographically closer, and hence faster to access, to the users and servicesthat need it.
Easier application development: Because Spanner is ACID-compliant and offers global strong consistency, developers working with Spanner don't have to add extra logic in their applications to deal with eventual consistency, making application development and subsequent maintenance faster and easier.
Spanner has three types of replicas: read-write replicas,read-only replicas, and witness replicas. The regions and replicationtopologies that form base instance configurationsare fixed. Base regional instance configurationsonly use read-write replicas. Base dual-region instance configurationsuse read-write and witness replicas, whilebase multi-region instance configurationsuse a combination of all three replica types. You can create custominstance configurations and add additional read-only replicas forregional and multi-region instance configurations.
Read-only replicas only support reads, but not writes. These replicas don'tvote for leaders or for committing writes, so they allow you to scale your readcapacity without increasing the quorum size needed for writes. Read-onlyreplicas:
If it is the nearest replica to your application, the read-only replica canusually serve stale reads without needing a round trip to the defaultleader region, assuming staleness is at least 15 seconds. You can alsouse directed reads to route read-only transactions and single reads to aspecific replica type or region in a multi-region instance configuration.For more information, see Directed reads.
Strong reads might require a round trip to the leader replica. The round tripis just for negotiating the timestamp, not shipping the actual data from theleader. The timestamp negotiation is a CPU efficient operation at the leader,and typically the data is already en-route. This communication is handledautomatically by the system.
You can create a custom regional or multi-region instance configurationand add optional read-only replicas to scale reads and support low latency stalereads. You can add locations listed under Optional Regionas an optional read-only replica. If you don't see your chosen read-onlyreplica location, you can request a new optional read-only replica region. Notethat you cannot change the replication topology of base instanceconfigurations, which are fixed.
All optional read-only replicas are subject to compute capacity and storagecosts. Furthermore, adding read-only replicas to a custominstance configuration doesn't change the Spanner SLAsof the instance configuration. If you choose to add a read-only replica to acontinent that is in a different continent than the leader region, we recommendadding a minimum of two read-only replicas. This helps maintain low read latencyin the event one of the read-only replicas becomes unavailable.
When you add read-only replica(s), the leader replica experiences morereplication load, which might affect performance. As a best practice, testperformance workloads in non-production instances in the custom instanceconfiguration first. You can refer to the Inter-Region Latency and Throughputbenchmark dashboard for medianinter-region latency data. For example, if you create a custom instanceconfiguration with the eur6 multi-region base configuration and an optionalread-only replica in us-east1, the expected strong read latency for aclient in us-east1 is about 100 milliseconds due to the round trip time to theleader region in europe-west4. Stale reads with sufficient staleness don'tincur the round trip and are therefore much faster. You can also use the Latencyby transaction type metric toview latency data for read-write and read-only type transactions.
Witness replicas don't support reads but do participate in voting to commitwrites. These replicas make it easier to achieve quorums for writes without thestorage and compute resources that are required by read-write replicas to storea full copy of data and serve reads. Witness replicas:
Client write requests are always processed at the leader replica first, even ifthere is a non-leader replica that's closer to the client, or if the leaderreplica is geographically distant from the client. If you use a multi-regioninstance configuration and your client application is located in a non-leaderregion, Spanner uses leader-aware routing to route read-writetransactions dynamically to reduce latency in your database. For moreinformation, see Leader-aware routing.
The leader replica logs the incoming write, and forwards it, in parallel, to theother replicas that are eligible to vote on that write. Each eligible replicacompletes its write, and then responds back to the leader with a vote on whetherthe write should be committed. The write is committed when a majority of votingreplicas (or "write quorum") agree to commit the write. In the background, allremaining (non-witness) replicas log the write. If a read-write or read-onlyreplica falls behind on logging writes, it can request the missing data fromanother replica to have a full, up-to-date copy of the data.
Single read methods (a read outside the context of a transaction) and readsin read-only transactions might require communicating with the leader,depending on the concurrency mode of the read. (Learn more about theseconcurrency modes in Read types.)
Stale read requests go to the closest available read-only or read-writereplica that is caught up to the timestamp of the request. This can be theleader replica if the leader is the closest replica to the client thatissued the read request.
Base multi-region configurationsuse a combination of read-write, read-only, and witness replicas, whereasbase dual-region configurationsuse read-write and witness replicas, andbase regional configurationsuse only read-write replicas. The reasons for this difference have to do withthe varying roles of replicas in writes and reads. For writes,Spanner needs a majority of voting replicas to agree on a commit inorder to commit a mutation. In other words, every write to a Spannerdatabase requires communication between voting replicas. To minimize the latencyof this communication, it is desirable to use the fewest number of votingreplicas, and to place these replicas as close together as possible. That's whybase regional configurations contain exactly three read-write replicas, each ofwhich is in its own availability zone, contains a full copy of your data, and isable to vote. If one replica fails, the other two can still form a write quorum,and because replicas in this configuration are in the same geographic region,network latencies are minimal.
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