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How is WeakHashMap differs from other HashMap?
WeakHashMap is a HashMap, with keys that are of a WeakReference type.
An entry in a WeakHashMap will automatically be removed when its key is no longer in ordinary use, meaning that there is no single Reference that point to that key. When the garbage collection (GC) process discards a key, its entry is effectively removed from the map, even though it is associated with WeakHashMap. i.e Garbage Collector dominates over WeakHashMap.
In HashMap, even if key is not having any reference which points to that key (is eligible for GC) is In reality not eligible for garbage collection because its associated with the entry object added in a bucket of hashMap. This means that the HashMap has dominance over the garbage collector.
What Is ElasticSearch?
Elasticsearch is a NoSQL database.
ElasticSearch is an open source Search Engine based on Apache Lucene as inverted Text Data structure and it is built with RESTful APIS.
We use it for Storing, searching and Managing
Logs
Search Backend with terrific speed and flexibility.
It mainly consist of
Indexes - similar to Database in relational Terms
Documents - Rows - JSON objects
Fields - Columns
It mainly has Read and write operation. you need to update this as soon as you update the main Database and Read it when FE needs Autocomplete feature.
What is Kafka
Apache Kafka is publish-subscribe based fault tolerant messaging system. It is fast, scalable and distributed by design.
It was initially thought of as a message queue and open-sourced by LinkedIn in 2011. Its community evolved Kafka to provide key capabilities:
Publish and Subscribe to streams of records, like a message queue.
Storage system so messages can be consumed asynchronously. Kafka writes data to a scalable disk structure and replicates for fault-tolerance. Producers can wait for write acknowledgments.
Stream processing with Kafka Streams API, enables complex aggregations or joins of input streams onto an output stream of processed data.
Traditional messaging models are queue and publish-subscribe. In a queue, each record goes to one consumer. In publish-subscribe, the record is received by all consumers.
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