GemFire Queries

Introduction

This example demonstrates simple queries on a VMware GemFire region.

In this example, two servers host a single partitioned region with entries that represent employee information. The example does queries through the API and presents example queries to be invoked through the gfsh command-line interface.

This example assumes that JDK11 and GemFire are installed.

Set up the cluster

Set directory gemfire-examples/queries to be the current working directory. Each step in this example specifies paths relative to that directory.

Build the example (with the EmployeeData class)

 $ ../gradlew build

Run a script that starts a locator and two servers, and then creates the example-region region.

 $ ../gradlew start

Run the example program

Run the example to populate example-region with employee information, print out the region information, and then programmatically invoke three queries, printing the results of each query.

 $ ../gradlew run

Issue gfsh commands to query the region

gfsh can also be used to issue queries.

If you have not already installed GemFire, the build step will have installed a gfsh executable for you at a path relative to the current working directory within a versioned directory:

../build/vmware-gemfire-<version>/bin/gfsh

You can use this relative path to invoke gfsh by substituting the appropriate <version>.

Start gfsh and connect to the cluster:

 $ gfsh
 ...
 gfsh>connect --locator=127.0.0.1[10334]

The quantity of entries may be observed with gfsh:

 gfsh>describe region --name=example-region

Here are some gfsh queries to try on the example-region region.

Query for all entries in the region

 gfsh>query --query="select * from /example-region"

Query for the email field of all entries in the region:

 gfsh>query --query="SELECT x.email FROM /example-region x"

Query for all entries that have a lastName field that starts with the letter ‘C’:

 gfsh>query --query="SELECT DISTINCT * FROM /example-region x WHERE x.lastName.startsWith('C')"

Exit gfsh:

 gfsh>exit

Shut down the cluster and (optionally) clean up the directory

Shut down the cluster.

 $ ../gradlew stop

If desired, clean up the generated directories containing logs:

 $ ../gradlew cleanServer

  Enter your code here ....