first commit

.gitattributes

@@ -0,0 +1,9 @@
+#
+# https://help.github.com/articles/dealing-with-line-endings/
+#
+# Linux start script should use lf
+/gradlew        text eol=lf
+
+# These are Windows script files and should use crlf
+*.bat           text eol=crlf
+

.gitignore

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+.gradle
+.vscode
+.idea
+
+bin
+build

build.gradle

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+plugins {
+    id 'groovy'
+    id 'application'
+    id "net.nemerosa.versioning" version "2.15.1"
+    id "com.netflix.nebula.ospackage" version "11.2.0"
+    id 'com.github.johnrengelman.shadow' version '8.1.1'
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    testImplementation 'org.codehaus.groovy:groovy:3.0.13'
+    testImplementation 'org.spockframework:spock-core:2.2-groovy-3.0'
+    testImplementation 'junit:junit:4.13.2'
+
+    annotationProcessor 'info.picocli:picocli-codegen:4.7.4'
+    implementation 'info.picocli:picocli:4.7.4'
+    implementation 'org.slf4j:slf4j-api:2.0.7'
+    implementation 'ch.qos.logback:logback-classic:1.3.8'
+}
+
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(8)
+    }
+    sourceCompatibility = JavaVersion.VERSION_1_8
+    targetCompatibility = JavaVersion.VERSION_1_8
+}
+
+application {
+    mainClass = 'biz.nellemann.memstress.Application'
+}
+
+tasks.named('test') {
+    useJUnitPlatform()
+}
+
+
+group = projectGroup
+version = projectVersion
+
+
+jar {
+    manifest {
+        attributes(
+                'Created-By'     : "Gradle ${gradle.gradleVersion}",
+                'Build-OS'       : "${System.properties['os.name']} ${System.properties['os.arch']} ${System.properties['os.version']}",
+                'Build-Jdk'      : "${System.properties['java.version']} (${System.properties['java.vendor']} ${System.properties['java.vm.version']})",
+                'Build-User'     : System.properties['user.name'],
+                'Build-Version'  : versioning.info.tag ?: (versioning.info.branch + "-" + versioning.info.build),
+                'Build-Revision' : versioning.info.commit,
+                'Build-Timestamp': new Date().format("yyyy-MM-dd'T'HH:mm:ss.SSSZ").toString(),
+        )
+    }
+}
+
+apply plugin: 'com.netflix.nebula.ospackage'
+ospackage {
+    packageName = 'memstress'
+    release = '1'
+    user = 'root'
+    packager = "Mark Nellemann <mark.nellemann@gmail.com>"
+
+    into '/opt/memstress'
+
+    from(shadowJar.outputs.files) {
+        into 'lib'
+    }
+
+    from('build/scriptsShadow') {
+        into 'bin'
+    }
+
+    from(['README.md', 'LICENSE']) {
+        into 'doc'
+    }
+
+}
+
+buildDeb {
+    dependsOn build, startShadowScripts
+}
+
+buildRpm {
+    dependsOn build, startShadowScripts
+    os = org.redline_rpm.header.Os.LINUX
+}
+
+tasks.register("packages") {
+    group "build"
+    dependsOn ":buildDeb"
+    dependsOn ":buildRpm"
+}

gradle.properties

@@ -0,0 +1,3 @@
+projectId               = memstress
+projectGroup            = biz.nellemann.memstress
+projectVersion          = 0.0.1

gradle/wrapper/gradle-wrapper.properties

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+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.1.1-bin.zip
+networkTimeout=10000
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

gradlew

@@ -0,0 +1,245 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/HEAD/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+# This is normally unused
+# shellcheck disable=SC2034
+APP_BASE_NAME=${0##*/}
+APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC3045
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC3045
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Collect all arguments for the java command;
+#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
+#     shell script including quotes and variable substitutions, so put them in
+#     double quotes to make sure that they get re-expanded; and
+#   * put everything else in single quotes, so that it's not re-expanded.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        org.gradle.wrapper.GradleWrapperMain \
+        "$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+    die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"

gradlew.bat

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+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+
+@if "%DEBUG%"=="" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%"=="" set DIRNAME=.
+@rem This is normally unused
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if %ERRORLEVEL% equ 0 goto execute
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if %ERRORLEVEL% equ 0 goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+set EXIT_CODE=%ERRORLEVEL%
+if %EXIT_CODE% equ 0 set EXIT_CODE=1
+if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
+exit /b %EXIT_CODE%
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

settings.gradle

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+/*
+ * This file was generated by the Gradle 'init' task.
+ *
+ * The settings file is used to specify which projects to include in your build.
+ *
+ * Detailed information about configuring a multi-project build in Gradle can be found
+ * in the user manual at https://docs.gradle.org/8.1.1/userguide/multi_project_builds.html
+ */
+
+plugins {
+    // Apply the foojay-resolver plugin to allow automatic download of JDKs
+    id 'org.gradle.toolchains.foojay-resolver-convention' version '0.4.0'
+}
+
+rootProject.name = 'memstress'

src/main/java/biz/nellemann/memstress/Application.java

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+package biz.nellemann.memstress;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import picocli.CommandLine;
+
+import java.util.Scanner;
+import java.util.concurrent.Callable;
+
+@CommandLine.Command(name = "memstress", mixinStandardHelpOptions = true, versionProvider = VersionProvider.class, description = "Memory performance measurement tool.")
+public class Application implements Callable<Integer> {
+
+    final Logger log = LoggerFactory.getLogger(Application.class);
+
+
+    @CommandLine.Option(names = { "-t", "--tables" }, paramLabel = "NUM", description = "Create this many tables [default: ${DEFAULT-VALUE}]")
+    int maxTables = 4;
+
+    @CommandLine.Option(names = { "-r", "--rows" }, paramLabel = "NUM", description = "Create this many rows pr. table [default: ${DEFAULT-VALUE}]")
+    int maxRowsPerTable = 10;
+
+    @CommandLine.Option(names = { "-d", "--data" }, paramLabel = "NUM", description = "Create this much data (MB) pr. row [default: ${DEFAULT-VALUE}]")
+    int maxDataPerRow = 100;
+
+
+    @Override
+    public Integer call() throws Exception {
+
+        MyDatabase database = new MyDatabase(maxTables, maxRowsPerTable, maxDataPerRow);
+        database.build("testDb");
+
+        System.out.println("TODO: How to search / read from data stored in rows?");
+
+        Scanner scanner = new Scanner(System.in);
+        System.out.println("Press ENTER to stop");
+        String s= scanner.nextLine();
+        scanner.close();
+
+        database.destroy("testDb");
+
+        return 0;
+    }
+
+
+    public static void main(String... args) {
+        int exitCode = new CommandLine(new Application()).execute(args);
+        System.exit(exitCode);
+    }
+
+
+}

src/main/java/biz/nellemann/memstress/MyDatabase.java

@@ -0,0 +1,89 @@
+package biz.nellemann.memstress;
+
+import biz.nellemann.memstress.db.Database;
+import biz.nellemann.memstress.db.DatabaseManager;
+import biz.nellemann.memstress.db.Table;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.nio.ByteBuffer;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.Random;
+
+public class MyDatabase {
+
+    final Logger log = LoggerFactory.getLogger(MyDatabase.class);
+
+    private final int BYTE_SIZE_1MB = 1_000_000;
+    private final int BYTE_SIZE_1GB = 1_000_000_000;
+
+    private final DatabaseManager databaseManager = new DatabaseManager();
+    private final Random random = new Random();
+
+    // Use when searching or using later?
+    private final ArrayList<Table> tables = new ArrayList<Table>();
+
+    private final int maxTables;
+    private final int maxRowsPerTable;
+    private final int maxDataPerRow;
+
+    public MyDatabase(int tables, int rows, int size) {
+        this.maxTables = tables;
+        this.maxRowsPerTable = rows;
+        this.maxDataPerRow = size;
+    }
+
+
+    public Database build(String dbName) {
+        Instant instant1 = Instant.now();
+        Database database = databaseManager.createDatabase(dbName);
+        for(int t = 1; t <= maxTables; t++) {
+
+            String tableName = String.format("table_%d", t);
+            log.info("Creating table \"{}\"", tableName);
+
+            Table table = database.createTable(tableName);
+
+            for(int r = 1; r <= maxRowsPerTable; r++) {
+                String rowIdx = String.format("%d_of_%d", r, maxRowsPerTable);
+                HashMap<String, ByteBuffer> map = new HashMap<String,ByteBuffer>();
+                for(int m = 1; m <= maxDataPerRow; m++) {
+                    map.put(randomString(128), ByteBuffer.wrap(randomBytes(BYTE_SIZE_1MB)) );
+                }
+                table.insertEntry(rowIdx, map);
+            }
+
+            tables.add(table);
+        }
+
+        Instant instant2 = Instant.now();
+        log.info("Done building in-memory database \"{}\" in {}", dbName, Duration.between(instant1, instant2));
+        return database;
+    }
+
+
+    String randomString(final int length) {
+        StringBuilder sb = new StringBuilder(length);
+        for(int l = 0; l < length; l++) {
+            sb.append( (char) random.nextInt(65_535));
+        }
+        return sb.toString();
+    }
+
+
+    byte[] randomBytes(final int length) {
+        byte[] randomArray = new byte[length];
+        random.nextBytes(randomArray);
+        return randomArray;
+    }
+
+
+    void destroy(final String dbName) {
+        databaseManager.deleteDatabase(dbName);
+    }
+
+
+}

src/main/java/biz/nellemann/memstress/VersionProvider.java

@@ -0,0 +1,20 @@
+package biz.nellemann.memstress;
+
+
+import picocli.CommandLine;
+
+import java.io.IOException;
+import java.util.jar.Attributes;
+import java.util.jar.Manifest;
+
+class VersionProvider implements CommandLine.IVersionProvider {
+
+    public String[] getVersion() throws IOException {
+
+        Manifest manifest = new Manifest(getClass().getResourceAsStream("/META-INF/MANIFEST.MF"));
+        Attributes attrs = manifest.getMainAttributes();
+
+        return new String[] { "${COMMAND-FULL-NAME} " + attrs.getValue("Build-Version") };
+    }
+
+}

src/main/java/biz/nellemann/memstress/db/Database.java

@@ -0,0 +1,65 @@
+/**
+ * Example taken from: https://medium.com/@mithoonkumar/design-an-in-memory-nosql-database-ood-428d48b68dfa
+ */
+package biz.nellemann.memstress.db;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.Date;
+import java.util.HashMap;
+
+public class Database {
+
+    final Logger log = LoggerFactory.getLogger(Database.class);
+
+    private String name;
+    private HashMap<String, Table> tableHashMap;
+    private Date createdAt;
+
+    public Database(String name) {
+        this.name = name;
+        this.tableHashMap = new HashMap<>();
+        this.createdAt = new Date();
+    }
+
+    public Table createTable(String tableName) {
+        if (tableHashMap.containsKey(tableName)) {
+            log.warn("createTable() - A table already exists with the given name: {}", tableName);
+        } else {
+            Table table = new Table(tableName);
+            tableHashMap.put(tableName, table);
+            log.debug("createTable() - Table successfully created: {}", tableName);
+        }
+        return tableHashMap.get(tableName);
+    }
+
+    public void dropTable(String tableName) {
+        tableHashMap.remove(tableName);
+        log.debug("dropTable() - Table successfully dropped: {}", tableName);
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public HashMap<String, Table> getTableHashMap() {
+        return tableHashMap;
+    }
+
+    public void setTableHashMap(HashMap<String, Table> tableHashMap) {
+        this.tableHashMap = tableHashMap;
+    }
+
+    public Date getCreatedAt() {
+        return createdAt;
+    }
+
+    public void setCreatedAt(Date createdAt) {
+        this.createdAt = createdAt;
+    }
+}

src/main/java/biz/nellemann/memstress/db/DatabaseManager.java

@@ -0,0 +1,36 @@
+/**
+ * Example taken from: https://medium.com/@mithoonkumar/design-an-in-memory-nosql-database-ood-428d48b68dfa
+ */
+package biz.nellemann.memstress.db;
+
+import java.util.HashMap;
+
+public class DatabaseManager {
+    private HashMap<String, Database> databaseHashMap;
+
+    public Database createDatabase(String databaseName) {
+        if (databaseHashMap.containsKey(databaseName)) {
+            System.out.println("A database already exists with this name");
+        } else {
+            databaseHashMap.put(databaseName, new Database(databaseName));
+        }
+        return databaseHashMap.get(databaseName);
+    }
+
+    public void deleteDatabase(String databaseName) {
+        databaseHashMap.remove(databaseName);
+    }
+
+    public DatabaseManager() {
+        this.databaseHashMap = new HashMap<>();
+    }
+
+    public HashMap<String, Database> getDatabaseHashMap() {
+        return databaseHashMap;
+    }
+
+    public void setDatabaseHashMap(HashMap<String, Database> databaseHashMap) {
+        this.databaseHashMap = databaseHashMap;
+    }
+
+}

src/main/java/biz/nellemann/memstress/db/Row.java

@@ -0,0 +1,60 @@
+/**
+ * Example taken from: https://medium.com/@mithoonkumar/design-an-in-memory-nosql-database-ood-428d48b68dfa
+ */
+package biz.nellemann.memstress.db;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.nio.ByteBuffer;
+import java.util.Date;
+import java.util.HashMap;
+
+public class Row {
+
+    final Logger log = LoggerFactory.getLogger(Row.class);
+
+    private String rowId;
+    private HashMap<String, ByteBuffer> columnValuesMap;
+    private Date createdAt;
+    private Date UpdatedAt;
+
+    public Row(String rowId, HashMap<String, ByteBuffer> columnsMap, Date createdAt, Date updatedAt) {
+        this.rowId = rowId;
+        this.columnValuesMap = columnsMap;
+        this.createdAt = createdAt;
+        UpdatedAt = updatedAt;
+    }
+
+    public HashMap<String, ByteBuffer> getColumnValuesMap() {
+        return columnValuesMap;
+    }
+
+    public void setColumnValuesMap(HashMap<String, ByteBuffer> columnValuesMap) {
+        this.columnValuesMap = columnValuesMap;
+    }
+
+    public String getRowId() {
+        return rowId;
+    }
+
+    public void setRowId(String rowId) {
+        this.rowId = rowId;
+    }
+
+    public Date getCreatedAt() {
+        return createdAt;
+    }
+
+    public void setCreatedAt(Date createdAt) {
+        this.createdAt = createdAt;
+    }
+
+    public Date getUpdatedAt() {
+        return UpdatedAt;
+    }
+
+    public void setUpdatedAt(Date updatedAt) {
+        UpdatedAt = updatedAt;
+    }
+}

src/main/java/biz/nellemann/memstress/db/Table.java

@@ -0,0 +1,79 @@
+/**
+ * Example taken from: https://medium.com/@mithoonkumar/design-an-in-memory-nosql-database-ood-428d48b68dfa
+ */
+package biz.nellemann.memstress.db;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.nio.ByteBuffer;
+import java.util.Date;
+import java.util.HashMap;
+
+public class Table {
+
+    final Logger log = LoggerFactory.getLogger(Table.class);
+
+    private String tableName;
+    private HashMap<String, Row> rows;
+    private Date createdAt;
+
+    public Table(String tableName) {
+        this.tableName = tableName;
+        this.rows = new HashMap<>();
+        this.createdAt = new Date();
+    }
+
+    public void insertEntry(String rowId, HashMap<String, ByteBuffer> columnsMap) {
+        if (rows.containsKey(rowId)) {
+            log.warn("insertEntry() - Insertion failed, duplicate primary key: {}", rowId);
+        } else {
+            Row row =  new Row(rowId, columnsMap, new Date(), new Date());
+            rows.put(rowId, row);
+            log.debug("insertEntry() - Row successfully added: {}", rowId);
+        }
+    }
+
+    public void updateEntry(String rowId, HashMap<String, ByteBuffer>valuesMap) {
+        Row row = rows.get(rowId);
+        valuesMap.forEach( (k, v) -> {
+            row.getColumnValuesMap().put(k, v);
+        });
+        log.debug("updateEntry() - Row successfully updated: {}", rowId);
+        row.setUpdatedAt(new Date());
+    }
+
+    public void deleteEntry(String rowId) {
+        log.debug("updateEntry() - Row successfully deleted: {}", rowId);
+        rows.remove(rowId);
+    }
+
+    public HashMap<String, ByteBuffer> readEntry(String rowId) {
+        return rows.get(rowId).getColumnValuesMap();
+    }
+
+
+    public HashMap<String, Row> getRows() {
+        return rows;
+    }
+
+    public void setRows(HashMap<String, Row> rows) {
+        this.rows = rows;
+    }
+
+    public String getTableName() {
+        return tableName;
+    }
+
+    public void setTableName(String tableName) {
+        this.tableName = tableName;
+    }
+
+    public Date getCreatedAt() {
+        return createdAt;
+    }
+
+    public void setCreatedAt(Date createdAt) {
+        this.createdAt = createdAt;
+    }
+}

src/main/resources/logback.xml

@@ -0,0 +1,14 @@
+<configuration>
+
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <withJansi>false</withJansi>
+        <encoder>
+            <pattern>%cyan(%d{yyyy-MM-dd HH:mm:ss.SSS}) %gray([%-10thread]) %highlight(%-5level) %magenta(%logger{12}) - %msg%n</pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+
+</configuration>

src/test/groovy/biz/nellemann/memstress/ApplicationTest.groovy

@@ -0,0 +1,10 @@
+/*
+ * This Spock specification was generated by the Gradle 'init' task.
+ */
+package biz.nellemann.memstress
+
+import spock.lang.Specification
+
+class ApplicationTest extends Specification {
+
+}