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Golang arrays performance

The scope of this article is just to illustrate the performance of arrays using the go language while iterating on different sizes of them, compared with accessing data directly (the same amount of items but not using an array).

The interesting thing is that:

  1. Accessing memory on small arrays(100 items) is slower than accessing memory on a single var in a for loop of the same size,
  2. Accessing memory on bigger arrays (10.000 items) is faster than accessing memory on a single var in a for loop of the same size,
  3. Accessing memory on more bigger arrays (100.000 items) is faster than accessing memory on a single var in a for loop of the same size.

Let's start illustrating the code that i'm using as the base example. This program is very simple, it prints out the times table of the numbers that you pass to it.

I've created two constants to pass the dimension of the arrays:

  • NUM i.e. the multiplicand
  • MULTIPLIERS i.e. the multipliers

If i set the NUM and the MULTIPLIERS constants to the value of 10 (100 items) i get:

Execution with array took 268.772µs
Execution without array took 180.132µs

If i set the NUM and the MULTIPLIERS constants to the value of 100 (10.000 items) i get:

Execution with array took 133.748902ms
Execution without array took 145.693206ms

If i set the NUM to the value of 1000 and the MULTIPLIERS to the value of 100 (100.000 items) i get:

Execution with array took 11.424318589s
Execution without array took 11.463020857s

Here is the code:

package main

import (

func main() {

    // Define our parameters here.
    // Change the values to see how performance change
    const NUM int = 10
    const MULTIPLIERS int = 10

    arrayStart := time.Now()
    fmt.Println(arrayTimesTable(NUM, MULTIPLIERS))
    elapsedArray := time.Since(arrayStart)
    //fmt.Printf("Execution took %s\n", elapsedArray)


    start := time.Now()
    fmt.Println(timesTable(NUM, MULTIPLIERS))
    elapsed := time.Since(start)

    fmt.Printf("Execution with array took %s\n", elapsedArray)
    fmt.Printf("Execution without array took %s\n", elapsed)

func arrayTimesTable(num, multipliers int) string {
    m := ""
    N := num
    M := multipliers

    arr := make([]int, N)
    for i := range arr {
        arr[i] = i + 1

    timesTable := make([]int, M)
    for k := range timesTable {
        timesTable[k] = k + 1

    for i := 0; i < len(arr); i++ {
        for t := 0; t < len(timesTable); t++ {
            res := [...]int{arr[i] * timesTable[t]}
            m += fmt.Sprintf("%v * %v: %v\n", i + 1, t + 1, res)
    return m

func timesTable(num int, multipliers int) string {
    m := ""
    for i := 0; i <= num; i++ {
        for t := 0; t <= multipliers; t++ {
            res := i * t
            m += fmt.Sprintf("%d * %d: %d\n", i, t, res)
    return m

Postgresql docker image with PostGIS extension

This image extends the official Postgres image, exactly the 9.6 tagged one.

All the customizations (bash scripts and DBs) are copied inside the /docker-entrypoint-initdb.d/ path.

Here is an example of the Dockerfile configuration:

FROM postgres:9.6

ENV POSTGIS_VERSION 2.4.4+dfsg-4.pgdg80+1

RUN apt-get update \
      && apt-cache showpkg postgresql-$PG_MAJOR-postgis-$POSTGIS_MAJOR \
      && apt-get install -y --no-install-recommends \
           postgresql-$PG_MAJOR-postgis-$POSTGIS_MAJOR=$POSTGIS_VERSION \
           postgresql-$PG_MAJOR-postgis-$POSTGIS_MAJOR-scripts=$POSTGIS_VERSION \
           postgis=$POSTGIS_VERSION \
      && rm -rf /var/lib/apt/lists/*

COPY init-db-postgis.sh /docker-entrypoint-initdb.d/init-db-postgis.sh
COPY update-postgis.sh /usr/local/bin/update-postgis.sh
COPY init-user-db.sh /docker-entrypoint-initdb.d/init-user-db.sh
COPY gis.sql.gz /docker-entrypoint-initdb.d/z.sql.gz

EXPOSE  5432

This way when the container starts users and DBs are created from scratch. It’s very important to remember that resources copied inside the /docker-entrypoint-initdb.d directory are executed in alphabetical order. I have renamed gis.sql.gz to z.sql.gz to be sure to have the my-user user created before the DB creation and restore phase.

Following an example of the init-user-db.sh script :

set -e

psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "$POSTGRES_DB" <<-EOSQL
    CREATE USER my-user;
    ALTER ROLE my-user WITH PASSWORD 'my-password';
        CREATE DATABASE "my-db-name";
        GRANT ALL PRIVILEGES ON DATABASE "my-db-name" TO my-user;

Here an example of the init-db-postgis.sh script:


set -e

# Perform all actions as $POSTGRES_USER

# Create the 'template_postgis' template db
"${psql[@]}" <<- 'EOSQL'
CREATE DATABASE template_postgis;
UPDATE pg_database SET datistemplate = TRUE WHERE datname = 'template_postgis';

# Load PostGIS into both template_database and $POSTGRES_DB
for DB in template_postgis "$POSTGRES_DB"; do
        echo "Loading PostGIS extensions into $DB"
        "${psql[@]}" --dbname="$DB" <<-'EOSQL'
                CREATE EXTENSION IF NOT EXISTS postgis;
                CREATE EXTENSION IF NOT EXISTS postgis_topology;
                CREATE EXTENSION IF NOT EXISTS fuzzystrmatch;
                CREATE EXTENSION IF NOT EXISTS postgis_tiger_geocoder;

And the update-postgis.sh script file:


set -e

# Perform all actions as $POSTGRES_USER


# Load PostGIS into both template_database and $POSTGRES_DB
for DB in template_postgis "$POSTGRES_DB" "${@}"; do
    echo "Updating PostGIS extensions '$DB' to $POSTGIS_VERSION"
    psql --dbname="$DB" -c "
        -- Upgrade PostGIS (includes raster)
        -- Upgrade Topology
        -- Install Tiger dependencies in case not already installed
        CREATE EXTENSION IF NOT EXISTS fuzzystrmatch;
        -- Upgrade US Tiger Geocoder
        ALTER EXTENSION postgis_tiger_geocoder UPDATE TO '$POSTGIS_VERSION';

List of GitHub commands

These are common Git commands used in various situations:

start a working area (see also: git help tutorial)
   clone     Clone a repository into a new directory
   init      Create an empty Git repository or reinitialize an existing one

work on the current change (see also: git help everyday)
   add       Add file contents to the index
   mv        Move or rename a file, a directory, or a symlink
   restore   Restore working tree files
   rm        Remove files from the working tree and from the index

examine the history and state (see also: git help revisions)
   bisect    Use binary search to find the commit that introduced a bug
   diff      Show changes between commits, commit and working tree, etc
   grep      Print lines matching a pattern
   log       Show commit logs
   show      Show various types of objects
   status    Show the working tree status

grow, mark and tweak your common history
   branch    List, create, or delete branches
   commit    Record changes to the repository
   merge     Join two or more development histories together
   rebase    Reapply commits on top of another base tip
   reset     Reset current HEAD to the specified state
   switch    Switch branches
   tag       Create, list, delete or verify a tag object signed with GPG

collaborate (see also: git help workflows)
   fetch     Download objects and refs from another repository
   pull      Fetch from and integrate with another repository or a local branch
   push      Update remote refs along with associated objects

'git help -a' and 'git help -g' list available subcommands and some
concept guides. See 'git help <command>' or 'git help <concept>'
to read about a specific subcommand or concept.
See 'git help git' for an overview of the system.

These GitHub commands are provided by hub:

   api            Low-level GitHub API request interface
   browse         Open a GitHub page in the default browser
   ci-status      Show the status of GitHub checks for a commit
   compare        Open a compare page on GitHub
   create         Create this repository on GitHub and add GitHub as origin
   delete         Delete a repository on GitHub
   fork           Make a fork of a remote repository on GitHub and add as remote
   gist           Make a gist
   issue          List or create GitHub issues
   pr             List or checkout GitHub pull requests
   pull-request   Open a pull request on GitHub
   release        List or create GitHub releases
   sync           Fetch git objects from upstream and update branches

Configure extended data types in Oracle

Prior to Oracle 12c, regardless of the character semantics used, the maximum size of a VARCHAR2, NVARCHAR2 and RAW columns in a database are as follows.

  • VARCHAR2 : 4000 bytes
  • NVARCHAR2 : 4000 bytes
  • RAW : 2000 bytes

With the introduction of Extended Data Types, Oracle 12c optionally increases these maximum sizes.

  • VARCHAR2 : 32767 bytes
  • NVARCHAR2 : 32767 bytes
  • RAW : 32767 bytes

Remember, these figures are in bytes, not characters. The total number of characters that can be stored will depend on the character sets being used.


An instance of Oracle 12c release 2

Connect to oracle with sqlplus

First thing first set the correct ORACLE_SID environment variable pointing to the DB that we wont to upgrade.


Now we can connect to the DB:

sqlplus sys as sysdba and when asked insert the password. Once we are logged in lets execute the instructions to extend the default maxstringsize parameter:

These instructions will modify the maxstringsize an all pluggable databases as well.

ALTER SYSTEM SET max_string_size=extended SCOPE=SPFILE;

cd $ORACLE_HOME/rdbms/admin/
$ORACLE_HOME/perl/bin/perl catcon.pl -d $ORACLE_HOME/rdbms/admin -l /tmp -b utl32k_output utl32k.sql

sqlplus sys as sysdba


For more detailed information look at the official Oracle documentation:


JBoss domain setup

Cluster configuration

Env setup

We will use a single installation and different configuration folders to simulate remote hosts:

unzip jboss-eap-7.1.0.zip -d $HOME/JBossDomain

then we will create virtual hosts directory structure

export EAP_DOMAIN=$HOME/JBossDomain
mkdir host0 host1 host2
cp -r jboss-eap-7.1/domain host0/
cp -r jboss-eap-7.1/domain host1/
cp -r jboss-eap-7.1/domain host2/

domain user configuration

We will create a management user only for the host0 node

cd $EAP_DOMAIN/jboss-eap-7.1/bin
./add-user.sh -dc $EAP_DOMAIN/host0/domain/configuration

Choose the following options:

Management User (mgmt-users.properties)
userName: admin
userPassword: Admin01#
GroupList: Empty, the user will be added by defautl to the ManagementRealm
Is this user going to be used for one AS process to connect etc etc: no

configure host authentication

We will create a second user for host authentication. We will need to repeat this step for all hosts.

cd $EAP_DOMAIN/jboss-eap-7.1/bin
./add-user.sh -dc $EAP_DOMAIN/host0/domain/configuration

Choose the following options:

Management User (mgmt-users.properties)
userName: slave
userPassword: Slave01#
GroupList: Empty, the user will be added by defautl to the ManagementRealm: yes
Is this user going to be used for one AS process to connect etc etc: yes

When the add-user script complete, an encrypted password is generated in the output. Keep the encrypted generated password and replace the default secrete value for host1 and host2 server identities.
create the same user for host1 and host2, this time in batch mode

cd $EAP_DOMAIN/jboss-eap-7.1/bin
./add-user.sh -dc $EAP_DOMAIN/host1/domain/configuration -r ManagementRealm -u slave -p Slave01# -ro admin,manager
./add-user.sh -dc $EAP_DOMAIN/host2/domain/configuration -r ManagementRealm -u slave -p Slave01# -ro admin,manager

replace the default secret value for host1 and host2


    <secret value="[your secret value]"/>

Set up the domain host and interfaces

We will update the host0/domain/host-master.xml file to set a correct hostname for preventing confusion in the domain configuration dashboard

cd host0/domain/configuration/
vi host-master.xml
edit host name to be host0-master
<host xmlns="urn:jboss:domain:4.1" name="host0-master">

Now we have to indicate that a host is a domain controller. We will locate the domain-controller section in the configurationfile and make sure its content matches the following structure:


The local tag indicates that this is a domain controller.

Configure slaves (host-slave.xml)

We will set up communications links between the domain controller and the hosts. For each host (host1, host2) edit the domain/configuration/host-slave.xml configuration file:

cd host1/domain/configuration
vi host-slave.xml
<host xmlns="urn:jboss:domain:4.1" name="host1">
cd host2/domain/configuration
vi host-slave.xml
<host xmlns="urn:jboss:domain:4.1" name="host2">

change the management interface default port to 19999 for host1 and 29999 for host2. Port 9999 is already used by the domain controller (host0):


<native-interface security-realm="ManagementRealm">
    <socket interface="management" port="${jboss.management.native.port:19999}"/>


<native-interface security-realm="ManagementRealm">
    <socket interface="management" port="${jboss.management.native.port:29999}"/>

Set up the right configuration so that the host can join the domain controller(repeat for host1 and host2):

    <remote security-realm="ManagementRealm">
        <static-discovery name="primary" protocol="${jboss.domain.master.protocol:remote}" host="${jboss.domain.master.address :}" port="${jboss.domain.master.port:9999}"/>

Remove the content of the servers tag (host1 and host2):

<servers> </servers>

Start the domain

Let's start the domain controller and the hosts:

cd $EAP_DOMAIN/jboss-eap-7.1/bin
./domain.sh -Djboss.domain.base.dir=../host0/domain/ --host-config=host-master.xml

start host1 from another termial or tab

./domain.sh -Djboss.domain.base.dir=../host1/domain/ --host-config=host-slave.xml

start host2 from another terminal or tab

./domain.sh -Djboss.domain.base.dir=../host2/domain/ --host-config=host-slave.xml

you can see the host registering in domain controller logs.

Now you can connect do the domain controller:

login: admin, Password: Admin01#

Create a server group

We will connect to the CLI and create a lab server group with the ha profile and the associated ha-sockets binding group.

cd $EAP_DOMAIN/jboss-eap-7.1/bin
./jboss-cli.sh -c
[domain@localhost:9999 /] /server-group=lab:add(profile=ha,socket-binding-group=ha-sockets)
    "outcome" => "success",
    "result" => "undefined",
    "server.groups" => "undefined"

Create some server instances

A server instance is cretaed on a host and belongs to one server group. Since we want to have many server instances on the same host, wi will shift the instances port offset, so we will add 100 to the base offset while moving from one server to another.

Host1 server creation

cd $EAP_DOMAIN/jboss-eap-7.1/bin
./jboss-cli.sh -c
[domain@localhost:9999 /] /host=host1/server-config=node11:add(group=lab,socket-binding-port-offset=100)

Host2 server creation

cd $EAP_DOMAIN/jboss-eap-7.1/bin
./jboss-cli.sh -c
[domain@localhost:9999 /] /host=host1/server-config=node21:add(group=lab,socket-binding-port-offset=200)

in this way we will have node11 on port 8180 and node21 on port 8280

Now let's start the servers

[domain@localhost:9999 /] /server-group=lab:start-servers

Configure Datasources

We will configure JBoss Domain for postgresql.

cd $EAP_DOMAIN/jboss-eap-7.1/modues/system/layers/base/
mkdir -p org/postgresql/jdbc/main
cp $HOME/Downloads/postgresql-9.4.1211.jar org/postgresql/jdbc/main/
vi org/postgresql/jdbc/main/module.xml

<?xml version="1.0" encoding="UTF-8"?>
<module xmlns="urn:jboss:module:1.3" name="org.postgresql.jdbc">
          <resource-root path="postgresql-9.4.1211.jar"/>
          <module name="javax.api"/>
          <module name="javax.transaction.api"/>
[domain@localhost:9999 /] /profile=ha/subsystem=datasources/jdbc-driver=postgresql:add(driver-name=postgresql,driver-module-name=org.postgresql.jdbc,driver-xa-datasource-class-name=org.postgresql.xa.PGXADataSource)

restart the domain.

JNDI configuration on Jboss web console

We will configure two datasources for the scope of this lab:
java:jboss/datasources/entandoDbPort2 and java:jboss/datasources/entandoDbServ2

Access to http://localhost:9990 user: admin password: Password01# and go to:


and select those options for create entandoDbPort2 JNDI:

  • Postgresql Datasource
  • Name: entandoDbPort2
  • JNDI Name: java:jboss/datasources/entandoDbPort2
  • Detected Driver: postgresql
  • Connection URL: jdbc:postgresql://localhost:5432/entandoDbPort2
  • user name: entando
  • password: entando

select those options for create entandoDbServ2 JNDI

  • Postgresql Datasource
  • Name: entandoDbServ2
  • JNDI Name: java:jboss/datasources/entandoDbServ2
  • Detected Driver: postgresql
  • Connection URL: jdbc:postgresql://localhost:5432/entandoDbServ2
  • user name: entando
  • password: entando


Postgresql dump and restore

Dumping with pg_dump

pg_dump -U [your username] [your schema] > [your-dump-file-name]_"$(date '+%F').sql" -h localhost -p 5433

Restoring with psql

psql -U postgres -h localhost -p 5433 -d [your schema] < [your-dump-file].sql

Reload configuration without restarting

SELECT pg_reload_conf();

Restore from a bz2 archive

bunzip2 your_dump.bz2 and then pg_restore -d [db-to-restore] -e [name-of-extracted-archive] -h [host] -U [user]

Backup and restore from a pod in a Kubernetes cluster

kubectl exec -it [your pod name] -- pg_dumpall -c -U postgres > /home/user/dump_db.sql
cat your_dump.sql | kubectl exec -it [your pod name] -- psql -U postgresp

Change owner recursively

select 'ALTER TABLE ' || t.tablename || ' OWNER TO [new user];'
 from  pg_tables t
 where schemaname = 'public';

Change owner of sequences recursively

select 'ALTER SEQUENCE ' || sequence_name || ' OWNER TO [your user];'
 from  information_schema.sequences t
 where sequence_schema = '[name of the schema]';

Delete all tables from a schema

select 'drop table if exists ' || tablename || ' cascade;' 
  from pg_tables
 where schemaname = '[name of the schema]'; 

Useful queries


Tweaks for JMeter

Tweaks for JMeter

This post highlights a few tips that may be necessary to identify the maximum concurrent throughput of one or more application servers with JMeter. They include TCP / IP tuning, load balancer tuning, and garbage collection tuning.

TCP / IP (Red Hat Enterprise Linux / RHEL)

When an HTTP request is made, an ephemeral port is allocated for the TCP / IP connection. The ephemeral port range is 32678 – 61000. After the client closes the connection, the connection is placed in the TIME-WAIT state for 60 seconds.

If JMeter (HttpClient) is sending thousands of HTTP requests per second and creating new TCP / IP connections, the system will run out of available ephemeral ports for allocation.

When JMeter is run, the following message may appear in the jmeter-server.log file if the JMeter server is unable to allocate a port to create a connection to the JMeter client to return the samples.

java.net.NoRouteToHostException: Cannot assign requested address

Otherwise, the following messages may appear in the JMeter JTL files:

Non HTTP response code: java.net.BindException
Non HTTP response message: Address already in use

The solution is to enable fast recycling and reuse TIME_WAIT sockets.

echo 1 > /proc/sys/net/ipv4/tcp_tw_recycle
echo 1 > /proc/sys/net/ipv4/tcp_tw_reuse

Other options include TCPFINTIMEOUT to reduce how long a connection is placed in the TIMEWAIT state and TCPTWREUSE to allow the system to reuse connections placed in the TIMEWAIT state. See this article for more information.

other resoruces: https://mapr.com/docs/52/AdvancedInstallation/SettingResourceLimitsOnCentOS.html