Skip to main content

ElasticSearch to RDBMS Glossary

In the early days of my playing with ElasticSearch, I remember struggling with some of the basic terminology and concepts. Naturally, many of us try to equate ElasticSearch, with what we know of RDBMS. To that end, I thought of posting this simple topic as a reference to others:

Node = DB Instance

One Database Instance
A node is simply one ElasticSearch instance (1 java process).
Consider this a running instance of MySQL. Just like you can have more than one MySQL instance running per machine on different ports… you can have more than one elasticsearch node running per machine on different ports.

Cluster = Database Cluster

1..N Nodes with the same Cluster Name.

Index = Database Schema

Similar to a Database, or Schema. Consider it a set of tables with some logical grouping. In ElasticSearch terms, an index is a Collection of Documents; where a “Document” is similar to a DB table.

Mapping Type = Database Table

ElasticSearch uses document definitions that act as tables. If you PUT (“Index”) a document in ElasticSearch, you will notice that it automatically tries to determine the property types. This is like inserting a JSON blob in MySQL, and MySQL determining the number of columns and column types (int, string, datetime, etc…) as it creates the DB table for you, on-the-fly.
Note: I’ve heard this refered to as “Type”, “Document Type”, and “Mapping Type”.

Shard = Uhhh…

I don’t think this one has a DB equivalent, but it’s likely the most important aspect listed here. A Shard is the smallest unit of worker in your cluster. It is one running Lucene instance. Shards are distributed across all of the nodes in your cluster and they are what makes ElasticSearch, elastic, sort-a-speak; giving your information and ES process redundancy.


Popular posts from this blog

Stretch a row if data overflows in jasper reports

It is very common that some columns of the report need to stretch to show all the content in that column. But  if you just specify the property " stretch with overflow' to that column(we called text field in jasper report world) , it will just stretch that column and won't change other columns, so the row could be ridiculous. Haven't find the solution from internet yet. So I just review the properties in iReport one by one and find two useful properties(the bold highlighted in example below) which resolve the problems.   example:
<band height="20" splitType="Stretch"> <textField isStretchWithOverflow="true" pattern="" isBlankWhenNull="true"> <reportElement stretchType="RelativeToTallestObject" mode="Opaque" x="192" y="0" width="183" height="20"/> <box leftPadding="2"> <pen lineWidth="0.25"/> …

JasperReports - Configuration Reference

Spring - Operations with jdbcTemplate

This class manages all the database communication and exception handling using a java.sql.Connection that is obtained from the provided DataSource. JdbcTemplate is a stateless and threadsafe class and you can safely instantiate a single instance to be used for each DAO.

Use of Callback Methods
JdbcTemplate is based on a template style of programming common to many other parts of Spring. Some method calls are handled entirely by the JdbcTemplate, while others require the calling class to provide callback methods that contain the implementation for parts of the JDBC workflow. This is another form of Inversion of Control. Your application code hands over the responsibility of managing the database access to the template class. The template class in turn calls back to your application code when it needs some detail processing filled in. These callback methods are allowed to throw a java.sql.SQLException, since the framework will be able to catch this exception and use its built-in excepti…