不爲也 比不能也

What If..."What if" questions are fun. "What if you had a time machine: when would you visit?" "What if you had one wish and it would come true: what would it be?" They're the types of hypothetical questions you can ask at a dinner party and get insights about what interests and motives somebody has if barriers were broken down. A few years ago at Elastic, we asked ourselves a "what if" that we ..

Elasticsearch provides failover capabilities by keeping multiple copies of your data in the cluster. In presence of network disruptions or failing nodes, changes might not make it to all the copies. This blog post showcases one of the internal mechanics of Elasticsearch to identify shard copies that are missing changes, providing an in-depth view on how two central components, the consensus modu..

UPDATE: This article refers to our hosted Elasticsearch offering by an older name, Found. Please note that Found is now known as Elastic Cloud.이 게시물은 기존에 Found라는 이름으로 제공된 Elasticsearch 서비스에 관한 것이다. Found은 이제 Elasticsearch Cloud로 알려져 있다.The previous article in this series, Elasticsearch from the Bottom Up, covered essential data structures within a single shard. In this article, we will look at t..

Primary shard allocationeditPreviously, primary shards were only assigned if a quorum of shard copies were found (configurable using index.recovery.initial_shards, now deprecated). In case where a primary had only a single replica, quorum was defined to be a single shard. This meant that any shard copy of an index with replication factor 1 could become primary, even it was a stale copy of the da..

Running a single node means that you have a single point of failure—there is no redundancy.Fortunately, all we need to do to protect ourselves from data loss is to start another node.단일 node를 실행한다는 것은 단일 장애 지점을 가지고 있다(복사본이 없다)는 것을 의미한다. 다행히, 데이터 손실을 피하기 위해, 해야 할 것은, 다른 node를 시작하는 것뿐이다.두 번째 node를 시작하려면To test what happens when you add a second node, you can start a new node in exactly the same wa..

What about scaling as the demand for our application grows? If we start a third node, our cluster reorganizes itself to look like Figure 4, “세 개의 node를 가진 cluster(shard는 부하를 분산하기 위하여 재할당되었다)”.응용프로그램에 대한 수요가 증가함에 따라, 확장하면 어떠할까? 세 번째 node를 시작하면, cluster는 Figure 4, “세 개의 node를 가진 cluster(shard는 부하를 분산하기 위하여 재할당되었다)”처럼 스스로를 인식할 것이다.Figure 4. 세 개의 node를 가진 cluster(shard는 부하를 분산하기 위하여 재할당되었다) One shar..

We’ve said that Elasticsearch can cope when nodes fail, so let’s go ahead and try it out. If we kill the first node, our cluster looks like Figure 6, “node 하나를 kill한 후의 cluster”.node에 장애가 발생할 경우, Elasticsearch는 대응할 수 있다고 했는데, 한 번 test해 보자. cluster의 첫 번째 node를 kill하면, Figure 6, “node 하나를 kill한 후의 cluster”처럼 보일 것이다.Figure 6. node 하나를 kill한 후의 cluster The node we killed was the master node. A clust..

When you index a document, it is stored on a single primary shard. How does Elasticsearch know which shard a document belongs to? When we create a new document, how does it know whether it should store that document on shard 1 or shard 2?document를 색인하면, 특정 primary shard에 저장된다. Elasticsearch는 document가 어느 shard에 속해 있는지 어떻게 알까? 새로운 document를 생성하면, document를 shard 1 또는 2 중 어느 shard에 저장하는지 어떻게 알까?Th..

For explanation purposes, let’s imagine that we have a cluster consisting of three nodes. It contains one index called blogs that has two primary shards. Each primary shard has two replicas. Copies of the same shard are never allocated to the same node, so our cluster looks something like Figure 8, “1개의 index와 3개의 node를 가진 cluster”.설명을 위해, 3개의 node를 가진 cluster를 가정해 보자. 그것은 2개의 primary shard를 가진 ..

Create, index, and delete requests are write operations, which must be successfully completed on the primary shard before they can be copied to any associated replica shards, as shown in Figure 9, “하나의 document를 생성, 색인 또는 삭제”.create, index, delete request는 쓰기 연산이다. Figure 9, “하나의 document를 생성, 색인 또는 삭제”에서 볼 수 있듯이, 관련된 replica shard에 복사하기 전에, primary shard에서 성공적으로 완료되어야 한다.Figure 9. 하나의 document를..