Elasticsearch on XGUGENG

IndexOutput: Lucene Index Output

Mon, 09 Apr 2018 11:25:40 +0800

Immediately following Indexwriter: Lucene Index Creation and Maintenance, IndexOutput, a random-access output stream. is used for all Lucene index output operations.

IndexWriter: Lucene Index Creation and Maintenance

Tue, 03 Apr 2018 14:37:02 +0800

An IndexWriter creates and maintains an index. It’s the basic Class defined in Lucene Core.

Fixing Elasticsearch with Red Status

Tue, 10 Oct 2017 10:05:01 +0800

Elasticsearch’s red status means at least one primary shard (and all of its replicas) is missing. This reminds you of missing data: searches will return partial results, and indexing into that shard will return an exception.

Directory in Lucene

Tue, 05 Sep 2017 16:26:31 +0800

Directory represents the storage location of the indexes and generally it is a list of files. These files are called index files. Index files are normally created once and then used for read operation or can be deleted.

Document in Lucene

Mon, 07 Aug 2017 18:52:01 +0800

In Lucene, a Document is the unit of search and index.

An index consists of a sequence of documents.
A document contains of one or more Fields.
A field is a named sequence of terms.
A term is a string.

In order to index data with Lucene, you must convert it to a stream of plain-text tokens firstly. Based on the stream, the document containing fields will be created. After that, you can call addDocument method in IndexWriter class to transmit it to index. During this procedure, analyzer may be used to make the data more suitable for indexing.

Guice Usage in Elasticsearch

Fri, 04 Aug 2017 15:58:27 +0800

The motivation of using Guice lists here: Motivation.

To create bindings, extend AbstractModule and override its configure method. In the method body, call bind() to specify each binding. These methods are type checked so the compiler can report errors if you use the wrong types. Once you’ve created your modules, pass them as arguments to Guice.createInjector() to build an injector.

Elasticsearch has a ModulesBuilder which is responsible for assembling modules.

public class ModulesBuilder implements Iterable<Module> {

    // container for all Module
    private final List<Module> modules = new ArrayList<>();

    // add new Modules into container
    public ModulesBuilder add(Module... newModules) {
        Collections.addAll(modules, newModules);
        return this;
    }

    @Override
    public Iterator<Module> iterator() {
        return modules.iterator();
    }

    public Injector createInjector() {
        Injector injector = Guice.createInjector(modules);
        ((InjectorImpl) injector).clearCache();
        // in ES, we always create all instances as if they are eager singletons
        // this allows for considerable memory savings (no need to store construction info) as well as cycles
        ((InjectorImpl) injector).readOnlyAllSingletons();
        return injector;
    }
}

A Node represents a node within a cluster. Node is made up of many Modules with the help of ModulesBuilder. Here is the short version of Node class.