quorum | permissioned implementation of Ethereum supporting data | Blockchain library
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QUESTION
I have a rabbitmq cluster with 3 nodes. One node has a durable and non-mirrored classic queue named test-queue
.
I have a spring boot app using spring-AMQP default connection factory new CachingConnectionFactory()
to firstly ensure the queue exists and then subscribe its messages. Everything works fine
Then I started a rolling update to the rabbitmq cluster, where node was being restarted one by one.
I observed following during this process from the log:
Upon start I saw below output
...ANSWER
Answered 2022-Apr-11 at 13:40See
https://docs.spring.io/spring-amqp/docs/current/reference/html/#declarationRetries
The number of retry attempts when passive queue declaration fails. Passive queue declaration occurs when the consumer starts or, when consuming from multiple queues, when not all queues were available during initialization. When none of the configured queues can be passively declared (for any reason) after the retries are exhausted, the container behavior is controlled by the 'missingQueuesFatal` property, described earlier.
and
https://docs.spring.io/spring-amqp/docs/current/reference/html/#failedDeclarationRetryInterval
The interval between passive queue declaration retry attempts. Passive queue declaration occurs when the consumer starts or, when consuming from multiple queues, when not all queues were available during initialization.
You can increase one or both of these from their defaults (3 and 5000 respectively).
QUESTION
I've got two EC2 instances running Artemis in the master-slave replication setup and I always perform rolling upgrade by shutting down the slave, upgrading it and starting it again. Then I do the same with the master. This no longer works for me while upgrading from 2.17 to 2.18. After upgrading one of the nodes I always get this message on that node:
...ANSWER
Answered 2022-Apr-07 at 14:42This bug was introduced via ARTEMIS-3340. It should be fixed in the next release (i.e. 2.22.0). Until then there's no work-around unfortunately.
You may consider creating a completely separate new live/backup pair and then using a DNS update to direct clients from the old pair to the new pair.
QUESTION
I am trying to run the HBase shell. The shell get starts but when I put any command it gives me this error:
...ANSWER
Answered 2022-Mar-07 at 09:31The problem is not related to hbase shell. The problem is that your HBase master cannot start, so the whole HBase cluster is not running.
Are you running one of the more recent versions of HBase? Like 2.4.x or so?
In this case, try to put the following entry into your hbase-site.xml (for the whole cluster):
QUESTION
I use MassTransit and RabbitMQ quorum queue for application integration. I send message using
...ANSWER
Answered 2022-Mar-14 at 16:37The general guidance is simple, don't couple your producers to your consumers.
You can start the receiver first so that it configures the queue properly (including the quorum settings).
Or you can set the Mandatory flag (RabbitMQ specified) so that Send throws an exception if the message is not delivered to a queue, and return to sending to the exchange.
QUESTION
I was reading through docs and encountered this part:
Consistency Level Quorum Reads Quorum Writes Strong Local Minority Global Majority Bounded Staleness Local Minority Local Majority Session Single Replica (using session token) Local Majority Consistent Prefix Single Replica Local Majority Eventual Single Replica Local MajoritySo let's say I have Strong consistency set as default (for writes).
And I want to override it for some queries.
It would matter only if I select between Strong
, Session
and Eventual
consistencies, because these are the ones with distinct Quorum Reads
.
Changing between Strong
and Bounded Staleness
or Consistent Prefix
and Eventual
wouldn't matter, because it's only for reads - writes are still configured with Strong
consistency.
Am I correct?
Edit: Though the sheer answer of @Mark doesn't satisfy me, it's complete for me with the comments, so I'm marking it as a solution.
To simplify, the answer is that effectively there's actually only 2 options in query relaxation: Strong
and Consistent Prefix
.
ANSWER
Answered 2022-Mar-08 at 19:06Relaxing the consistency level on reads, including queries does have an impact but that impact is one of cost. Strong and Bounded Staleness are Local Minority. This means reads are done on two replicas and the LSN's are compared between them. If they match the data is consistent. If they do not match, the item with the greater LSN is returned as it is the most recent write.
Because data is read from two replicas, the RU/s cost is 2x that of reads from Session or weaker consistency.
It is precisely because of this reduced cost that users may want to weaken their consistency on reads. If you're building an app that does not require perfect consistency and the data can lag by a small amount of time, this is perfectly suitable and less expensive way to do it. Particularly if the queries are done with high concurrency.
It's worth pointing out that relaxing the consistency level to session will result in Consistent Prefix being used. Session consistency requires the session token which today is only scoped to a single partition key range id. Since queries can span multiple partition key range values your effective consistency level used is essentially consistent prefix.
QUESTION
In cosmos DB, one replica-set consists of 4 replicas. It has one leader and 3 followers (including a forwarder).
I assume that all updates go through the leader first and the leader is the first one to be updated when updates come in the replica-set.
If my assumption is correct, a reader does not have to read many replicas. It only needs to check the leaders in each replica-set to figure out latest updates.
For example, Cosmos DB documentation says that in case of eventual and consistent prefix consistency models, quorum reads is accessing one single replica. As far as I understand it, the single replica can be any replica in a region. But, if a reader needs to read a update from a replica, does it have to be a leader replica?
...ANSWER
Answered 2022-Mar-03 at 19:16For read operations on Eventual consistency, it can be any of the 4 replicas that are available, so the read will land on any of them, not particularly the leader.
QUESTION
I have a high availability cluster with two nodes, with a resource for drbd, a virtual IP and the mariaDB files shared on the drbd partition.
Everything seems to work OK, but drbd is not syncing the latest files I have created, even though drbd status tells me they are UpToDate.
...ANSWER
Answered 2022-Feb-23 at 09:15I have found a Split-Brain that did not appear in the status of pcs.
QUESTION
I have a git repository I am attempting to move to github from bitbucket. This is something I have done before without much difficulty, both using the github importer tool and manually sending up a repo. In this particular case, however, my repository seems to have an issue in its history, which causes github to fail. Notably, when I run git fsck, I get:
...ANSWER
Answered 2022-Feb-10 at 22:00Here's the actual commit in question (raw content), and the problem:
QUESTION
Consider that we are running Raft on 3 machines: A, B, C and let A be the leader. There is a network partition that splits C, from A, B. Call the current term t. A and B remain on term 2, with no additional messages besides periodic heartbeats. At this time, C enters candidate state and increments term to 3, votes for itself, times out, and repeats. After say 10 cycles, the network partition is resolved. Now the state is A[2], B[2], C[12]; C will reject AppendEntries RPC from A as the term 2 is less than its current term, 10; C cannot assemble a quorum and will continue to run the leader election protocol as a candidate, and become increasingly more divergent from the current term value of A and B.
The question is then, how does Raft (or Raft-derived implementations) handle this issue? Some thoughts I had included:
- Such a situation is an availability issue, rather than a safety violation. Ignore and let human operators handle by killing or resetting C
- Exponential backoff to decrease the divergence of C per elections
- Have C use lastApplied instead of currentTerm as the basis for rejecting or accepting the AppendEntries RPC. That is, we trust the log as the source of truth for terms, rather than currentTerm value. This is already used to ensure that C would not win as per the Election Restriction, however the paper seems to indicate that this "up-to-date" property is a grounds for not voting for C, but is not grounds for C to acquiesce and reset to a follower.
Note: terminology as per In Search of an Understandable Consensus Algorithm (Extended Version)
ANSWER
Answered 2022-Jan-12 at 00:33When C rejects an AppendEntries RPC from the leader A, it will return its now > 2
term. Raft replicas always recognize greater terms, so that in turn will cause the leader to step down and start a new election. Eventually, the cluster will converge on a new term that’s > 2
and which is >=
C’s term.
This is an oft discussed (in the Raft dev community) somewhat inconvenient scenario that can cause unnecessary churn in Raft clusters. To guard against it, the Raft dissertation — and most real-world implementations — introduce and use the so-called “pre-vote protocol.” The pre-vote protocol essentially dictates that before becoming a candidate, a follower must first determine whether it can win an election by asking its peers. In the scenario you described above, C would ask for a pre-vote from A and B, and because of the network partition it would not receive any votes. So, C would never transition to the candidate role, never increment the term, and thus never present a term > 2
after the partition heals. Thus, you’ve eliminated the churn.
You can read more about the pre-vote protocol in Diego’s dissertation.
QUESTION
I have a Google sheets with 65 lines set up for data. In every row some of the cells use dropdown list and others use an if formulas based on the selections of the dropdown choices. The final cell (CQ), through the use of an if statement in the cell, populates as follows;
A) Returns "" if all other calculated cells in the row are blank B) Returns "DATA INCOMPLETE" if all the other calculated cells in the row do not meet specific criteria C) Returns "COMPLETED" if all calculated cells meet the specific criteria.
My sheet currently has data in 10 lines however it is trying to generate 65 PDF files. In functionNMPRBulkPDF it is suppose to stop when it reaches a blank row however that is not happening. I believe this is occurring because it thinks a row is not blank because either:
A) it sees the dropdown box as having data or B) it thinks the if formula is actual data even if the return is blank ("")
I am not sure which.
What I would like to be able to do is to use last cell in the row (CQ) to determine if the row should have a PDF file created for it. If the entry is "" or "COMPLETED" I would like to skip the row and go on to the next one. Or in other words only print the ones with "DATA INCOMPLETE" in that last cell (CQ)
I have this working well other than this issue so any help will be highly appreciated. Please have patience with me as this is my first foray into Google Script and I am totally self taught.
Here is my script
...ANSWER
Answered 2021-Oct-19 at 08:45I believe your goal is as follows.
- You want to check the column "CQ". When the value of column "CQ" is
DATA INCOMPLETE
, you want to skip in the loop ofdata.forEach(row => {,,,})
.
In this case, how about the following modification? I think that in your situation, there are several methods.
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