What Database Does Elastic Search Use?

Question
What SQL database underlies Elastic Search?

Answer
There is no relational database for Elastic Search.

Elastic Search will have a cluster that is composed of nodes. Nodes are composed of indexes. Indexes are supported by shards. Shards have primary and replica copies. The replica copies vary. The shards are essentially Lucene indexes (according to this site).

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How Do You Install and Configure the rdf4j Server and Workbench GUI?

Problem scenario
You want to use the rdf4j (Resource Description Framework for Java). You want to install the rdf4j server and workbench. You are using Debian 9 Linux. What should you do?

Solution
Prerequisites
i. We recommend having a 30 GB of hard disk free.

ii. We recommend having 5.75 GB of RAM (it can be a combination of RAM and swap space).

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How Do You Create a Database in MongoDB Not Using using Compass (the GUI)?

Problem scenario
You want to create a database in MongoDB using the CLI. How do you do this from a Linux server and then add a document to the database you just created?

Solution
Prerequisite

Install MongoDB on a Linux server; if you need assistance, see this posting.

Procedures

1.a. Enter the MongoDB shell: /usr/bin/mongo

1.b.

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How Do You Troubleshoot Cassandra when It Hangs on the Message “ColumnFamilyStore.java Initializing”?

Problem scenario
You start Cassandra with this command: ./bin/cassandra
You see one of the following messages:

INFO [MigrationStage:1] 2018-04-06 19:01:07,144 ColumnFamilyStore.java:391 – Initializing system_auth.resource_role_permissons_index
INFO [MigrationStage:1] 2018-04-06 19:01:07,163 ColumnFamilyStore.java:391 – Initializing system_auth.role_members

No progress is happening. What should you do?

Solution
Possible Solution #1. Try rebooting the server. This could help the problem.

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What Do You Do when Cassandra Stalls on “Initializing IndexInfo”?

Problem scenario
When you start Cassandra you see a message such as this:

INFO [main] 2018-02-03 08:45:55,257 ColumnFamilyStore.java:389 – Initializing system.IndexInfo

What should you do?

Possible Solution #1
Try rebooting the server. This could help the problem.

Possible Solution #2
This next one is merely a workaround. It is not a best practice.

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Why Would a MongoDB Container Work on an Ubuntu Host but Not a SUSE Host?

Problem scenario
You have two Linux servers in AWS, and each one has the same flavor (i.e., same amount of RAM and same number of processors). One is Ubuntu and another is SUSE. These commands will create working containers in Ubuntu:

docker run –name name1-mongo -d mongo
docker run –name name2-mongo -d mongo:2

This command will not create a working container in SUSE:

docker run –name name2-mongo -d mongo:2

The container that is created will never start.

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How Do You Install Apache Rya on Any Distribution of Linux?

Problem Scenario
You want to install Apache Rya on Linux. What do you do?

Solution

Prerequisites
i. You need a server with at least 5 GB of total memory. You can create swap space with this posting. (Remember that 1 GB of RAM and 2 GB of swap space will be insufficient for installing Rya.)
ii.

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How Do You Run Some Cassandra Commands to Create a Table?

Problem scenario
You want to create a table in Cassandra.  How do you do this?

Solution
Prerequisites
Install and configure Cassandra.  If you do not know how, click on the link for the distribution of Linux that you have:

Debian or Ubuntu
CentOS/RHEL/Fedora
SUSE

Procedures
You will have to create a keyspace,

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How Do You Troubleshoot the Error “intx ThreadPriorityPolicy=42 is outside the allowed range [ 0 … 1 ] “?

Problem scenario
You try to start Cassandra but you get this error:

“[0.000s][warning][gc] -Xloggc is deprecated. Will use -Xlog:gc:./bin/../logs/gc.log instead.
intx ThreadPriorityPolicy=42 is outside the allowed range [ 0 … 1 ]
Improperly specified VM option ‘ThreadPriorityPolicy=42’
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.”

Possible solution #1
Migrate to Linux SUSE or a Red Hat family version of Linux (e.g.,

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How Do You Enter Data into a Cassandra Table?

Problem scenario
You want to insert data into a Cassandra table.  How do you do this?

Solution
Prerequisites

Install and configure Cassandra.  If you do not know how, click on this link and go to “Possible Solution #5” at the bottom to determine the distribution of Linux that you have.

Procedures
1.  Create the table with this command:
CREATE TABLE contint(
  

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