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Thuan Duong thuandt

  • Ho Chi Minh, Vietnam
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# Setup OpenWRT router
set -e
if [ -f /etc/upgraded ]; then
echo "router has been configured properly!"
if ping -q -c 1 -W 1 >/dev/null; then
echo "start reconfigure router"

Quick Tips for Fast Code on the JVM

I was talking to a coworker recently about general techniques that almost always form the core of any effort to write very fast, down-to-the-metal hot path code on the JVM, and they pointed out that there really isn't a particularly good place to go for this information. It occurred to me that, really, I had more or less picked up all of it by word of mouth and experience, and there just aren't any good reference sources on the topic. So… here's my word of mouth.

This is by no means a comprehensive gist. It's also important to understand that the techniques that I outline in here are not 100% absolute either. Performance on the JVM is an incredibly complicated subject, and while there are rules that almost always hold true, the "almost" remains very salient. Also, for many or even most applications, there will be other techniques that I'm not mentioning which will have a greater impact. JMH, Java Flight Recorder, and a good profiler are your very best friend! Mea

thuandt / Choosing a deployment tool - ansible vs puppet vs chef vs salt


  • no upfront installation/agents on remote/slave machines - ssh should be enough
  • application components should use third-party software, e.g. HDFS, Spark's cluster, deployed separately
  • configuration templating
  • environment requires/asserts, i.e. we need a JVM in a given version before doing deployment
  • deployment process run from Jenkins


# List unique values in a DataFrame column
# h/t @makmanalp for the updated syntax!
df['Column Name'].unique()
# Convert Series datatype to numeric (will error if column has non-numeric values)
# h/t @makmanalp
pd.to_numeric(df['Column Name'])
# Convert Series datatype to numeric, changing non-numeric values to NaN
# h/t @makmanalp for the updated syntax!
thuandt /
Created Jan 9, 2017
Random delay for cron.daily, cron.weekly, cron.monthly

Random delay for cron.daily, cron.weekly, cron.monthly


Wouldn’t it be nice if cron’s daily, weekly and monthly jobs could be run with a slight offset? At least that’s what I thought when 20+ servers were hitting my backup infrastructure at once. The scripts in /etc/cron.daily, /etc/cron.weekly and /etc/cron.monthly are triggered directly from crontab at fixed times. Here’s what /etc/crontab looks like in Ubuntu Server 16.04:

thuandt /
Created Nov 20, 2016
Working with GKE cluster using Google Cloud SDK

GCP & GKE setup

$ gcloud auth application-default login
$ gcloud config set core/project ${GCP_PROJECT}
$ gcloud config set core/account ${SERVICE_ACCOUNT}
$ gcloud config set compute/region ${REGION}
$ gcloud config set compute/zone ${ZONE}
$ gcloud config set container/cluster ${CLUSTER_NAME}
# gcloud config set container/use_client_certificate True
View types.markdown


A type is a collection of possible values. An integer can have values 0, 1, 2, 3, etc.; a boolean can have values true and false. We can imagine any type we like: for example, a HighFive type that allows the values "hi" or 5, but nothing else. It's not a string and it's not an integer; it's its own, separate type.

Statically typed languages constrain variables' types: the programming language might know, for example, that x is an Integer. In that case, the programmer isn't allowed to say x = true; that would be an invalid program. The compiler will refuse to compile it, so we can't even run it.

thuandt / st_icon_512.png
Last active Apr 1, 2020
Replace Sublime Text Icon in Ubuntu
thuandt /
Created Mar 31, 2016


The strongest valid recommendation based on exact fitting of blocks into stripes is the following: If you are using RAID-Z with 512-byte sector devices with recordsize=4K or 8K and compression=off (but you probably want compression=lz4): use at least 5 disks with RAIDZ1; use at least 6 disks with RAIDZ2; and use at least 11 disks with RAIDZ3.

To summarize: Use RAID-Z. Not too wide. Enable compression.


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  • I am thuandt on github.
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To claim this, I am signing this object: