Nov 25, 2015

Apache htaccess Debugging Ugly. This Will Save Your A$$...

If you ever created redirection rules in Apache htaccess or configuration file, you probably know that things can easily turn ugly. Without debugging tools and with long testing cycle, the debugging can be painful.

The htaccess tester tool can solve your issues: just place your requested URL and the actual htaccess that is being used, and you will get the actual result.

Keep Performing,
Moshe Kaplan

Sep 20, 2015

5 Immidiate Steps to Take Care of Your MongoDB Performance

Do you face some performance issues in your MongoDB setup?
In this case use the following steps to provide some first aid to your system and gain some space for a long term architecture (such as Sharding)

Step 1: Enable slow queries
Get intelligence about your system behavior and performance bottlenecks. Usually there is a high correlation between the slow queries and your performance bottleneck, so use the following method to enable your system profiling collection:

db.setProfilingLevel(1, 100);

Step 2: Use explain

Explore the problematic queries using explain. You can also use mtools to analyze the logged queries to find high frequent ones.

Step 3: Create indexes
Your analysis should result with new indexes in order to improve the queries
Don't forget to use index buildup in the background to avoid collections locking and system downtime.

Step 4: Use sparse indexes to reduce the size of the indexes
If you use sparse documents, and heavily using the $exists key words in your queries, using sparse indexes (that includes only documents that includes your field) can minimize your index size the boost your query performance.

Step 5: Use secondary preferred to offload queries to slaves
You probably have a replica set and it's waste of resources not using your slaves for read queries (especially for reporting and search operations).
By changing your connection string to secondary preferred, your application will try to run read queries on the slaves before doing that on your master.
Bottom Line
Using these simple method, you can gain time and space before hitting the wall.

Keep Performing,
Moshe Kaplan

Sep 2, 2015

Prepare for Failure in Your AWS Environment

In the cloud everything can happen. 
Actually everything will happen.

Therefore, in your design, you should be ready for failures: even if you expect your disk mounts to be there for you, they might not be. And you are doing auto scaling, it is most likely that one in a time they won't be there for you.

Therefore, to avoid hanging servers due to failure to mount disks and bad messages as the follow: "The disk drive for /tmp is not ready yet or not present", make sure your servers are not bound by your disks (otherwise you will not be able to contact your servers, or your OpsWorks will notify you that the server is booting forever).

Avoiding Waiting for Your Mount
The secret is a small option: nobootwait that will make sure your server is not waiting for the mount to be ready. You can configure it in your /etc/fstab, or even better in your Chef recipe:
mount "/tmp" do
  device ""
  fstype "nfs"
  options "rw,nobootwait"
  action [:mount, :enable]

Bottom Line
The right design will help you keep you system running in a cloud based environment

Keep Performing,
Moshe Kaplan

Jul 31, 2015

MongoDB 3.0 WiredTiger is Big News for Multi Tenant Deployments

A database per tenant is a common practice in multi tenant systems.
Why? Well, first it s easier to implement as you don't need to record the tenant id in every document, and second, it easier to avoid security issues by compromising the tenant id.

MongoDB 3.0 Storage Engines
MongoDB introduced a new concept in version 3.0 (that is familiar for MySQL users): you can select your preferred storage engine. You can continue using the old MMAPv1 storage engine (that is still the default one for version 3.0) or select WiredTiger that offers compression, document level lock and better performance in some cases.

What is Wrong with MMAPv1
MMAPv1 creates for every new database a data file that its minimal size is ~70MB (and this one is being filled, a new file is created with a doubled size). 
This may not be an issue for large size databases, but if your system design is built on a large number of tenants, that many of them will not have more than few records (lets say trial tenants that decided not to go on w/ your system), you are going to have 70GB disk allocation for every 1,000 tenants. 
This behavior will result in another side affect: very high IO usage (mostly for read), that is due to the need to read every time a large file in order to update or insert very few rows.

WiredTiger Comes to Rescue
WiredTiger includes a compression method that can cut 85% of your storage needs in a large database (trust me that I saw this number in a 10TB billing system). That is great, but more important, it does not allocate this 70MB file per each database (it satisfies with two small files for indexes and data).
The result: for a 3,500 tenants system, the database was shrunk from 330GB to under 1GB... not to mention that IOPS that were dropped from 12,000 to 600...

Bottom Line
If you are using MongoDB for multi tenant system, WiredTiger can cut your storage needs in 99% and your IOPS in 95%. This can save a fortune.

Keep Performing,
Moshe Kaplan

May 30, 2015

1 Click from Code to Prod: Spark, Scala, sbt, Intellij and Hadoop

You will probably will find dozens of Q&A articles how to create a new scala project using Intellij and submit it to a remote Hadoop based Spark cluster. However, none of them is actually complete and shows the full picture.
This post is going to save you a lot of time, so stay tuned...

Expected Outcome: an environment that will let you in one click move from coding your Scala to submitting it to a remote YARN based Spark cluster.

Note: some issues like "no spaces" may be overcome using double quotes or other methods, but we recommend you to follow the process and make it the simple way to avoid unexpected outcomes.

  1. Install JDK. Make sure JDK is placed in a folder w/o spaces (for example C:\Java)
  2. Configure the JAVA_HOME environment variable to you installation location
  3. Download and install the latest Intellij IDE
  4. Install the Intellij Scala plugin
  5. Download and install scala. Again make sure scala is placed in a folder w/o spaces (for example C:\scala)
  6. Set the environment variable for Scala
  7. Download and install sbt 0.13.8. Again make sure sbt is placed in a folder w/o spaces (for example C:\sbt)
  8. Add the sbt folder to the PATH environment variable
  9. In windows, you will need 1) to download winutils.exe; 2) create Hadoop folder; 3) and2) place in a bin folder inside a in order to avoid the following error:
    Failed to locate the winutils binary in the hadoop binary path Could not locate executable null\bin\winutils.exe in the Hadoop binaries.
  10. If your environment is connected to the internet using a proxy add the following proxy parameter of both HTTP and HTTPS to the JAVA_OPTIONS environment variable: -Dhttp.proxyPort=8080 -Dhttps.proxyPort=8080
Note: when working w/ Intellij, consider using the early access program for quick fixes especially in a dynamic environment like Scala and Spark

Create the Initial Project
  1. Create a new Scala (and not an sbt on) project in Intellij
  2. Select the right JDK version (based on the installation you made before)
  3. Select the right Scala SDK to match the cluster (see below): click on create and select the right one (or click on download and get it):
Create the Basic Project Files
This should be done in the file system and not inside the Intellij IDE to avoid surprises.
  1. Create a build.sbt file in the project root. Please notice:

    1. Matching the Spark client and cluster versions.
    2. Matching the Hadoop client and cluster versions.
    3. Matching the Scala and Spark version by looking for the spark-core package in Maven Central. In our case you should look for the spark cluster version (1.2.0) and then get the matching Scala version (2.10) from the ArtifactId. The minor version can be found in the Scala site.

      The various Spark-core versions and matching the Spark and Scala versions
    4. Adding the "provided" keyword to the library dependencies in order to avoid jar clashes when building the project:
      [error] (*:assembly) deduplicate: different file contents found in the following:
      [error] \.ivy2\cache\javax.activation\activation\jars\activation-1.1.jar:javax/activation/ActivationDataFlavor.class
      [error] \.ivy2\cache\org.eclipse.jetty.orbit\javax.activation\orbits\javax.activation-1.1.0.v201105071233.jar:javax/activation/ActivationDataFlavor.class
    5. Not using the provided key: in order to avoid cases where sbt assembly run correctly, but actually the make (or sbt run) does not, you should include the following reincluding in your build.sbt (and not in your assembly.sbt): run in Compile <<= Defaults.runTask(fullClasspath in Compile, mainClass in (Compile, run), runner in (Compile, run))
    6. Exclude javax.servlet file to avoid the following errors:
      [error] (run-main-0) java.lang.SecurityException: class "javax.servlet.FilterRegistration"'s signer information does not match signer information of other classes in the same package
      java.lang.SecurityException: class "javax.servlet.FilterRegistration"'s signer information does not match signer information of other classes in the same package
    7.         at java.lang.ClassLoader.checkCerts(
    8.         at java.lang.ClassLoader.preDefineClass(
    9.         at java.lang.ClassLoader.defineClass(
    10. Keeping a spaced line between each two lines.
    11. From the command line in the project root run: 
      1. sbt
      2. sbt update
      3. sbt assembly
      4. sbt run
    12. If you get during running the following exception, do worry, it is just a cleanup issue and you can disregard it:
      ERROR Utils: Uncaught exception in thread SparkListenerBus
              at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(
  2. Create a /project/assembly.sbt file and run sbt assembly to verify the project jar is being created: sbt assembly. Using this you will be able to avoid:
    [error] Not a valid command: assembly
    [error] Not a valid project ID: assembly
    [error] Not a valid configuration: assembly
    [error] Not a valid key: assembly
    [error] assembly
  3. Create a /main/scala/SimpleApp.scala file (or any other original name for your project main file). Please notice to include
    1. The spark conf should include your spark master that will serve your jar using setMaster, in order to avoid the following error:
      "A master URL must be set in your configuration"
    2. If you have limited resources (and you will have), configure the number of used cores and the allocated memory per core.
    3. The path where your compiled jar is located using setJars. After building your project in the first time you will be able to find it inside the target folder in your project. If you want configure setJars, you will get messages that Spark cannot find your Jar
The /build.sbt file:
name := "SimpleApp"

scalaVersion := "2.10.4"

run in Compile <<= Defaults.runTask(fullClasspath in Compile, mainClass in (Compile, run), runner in (Compile, run))

libraryDependencies += "org.apache.hadoop" % "hadoop-client" % "2.5.0" % "provided" excludeAll ExclusionRule(organization = "javax.servlet")

libraryDependencies += "org.apache.hadoop" % "hadoop-hdfs" % "2.5.0" % "provided" excludeAll ExclusionRule(organization = "javax.servlet")

libraryDependencies += "org.apache.spark" %% "spark-core" % "1.2.0" % "provided"

The /project/assembly.sbt file:
addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.13.0")

The /main/scala/SimpleApp.scala file:
import org.apache.spark.SparkContext
import org.apache.spark.SparkContext._
import org.apache.spark.SparkConf

object SimpleApp {
  def main(args: Array[String]) {
    val logFile = "hdfs://*" 
    val conf = new SparkConf()
        .setAppName("Simple Application")
        .set("spark.executor.memory", "64m")
        .set("spark.cores.max", "4")
    val sc = new SparkContext(conf)
    val logData = sc.textFile(logFile, 2).cache()
    val numAs = logData.filter(line => line.contains("a")).count()
    val numBs = logData.filter(line => line.contains("b")).count()
    println("Lines with a: %s, Lines with b: %s".format(numAs, numBs))

Arrange the IDE and Submit your First Job
  1. Create a new configuration.
  2. Add sbt assembly to "the before launch" configuration in order to generate a jar file:
    1. Add a new task to the "Before Launch"
    2. Add a new external tool
    3. Set the sbt location in the program and "assembly" in parameters
Bottom Line
It may take a little time to launch a proper Scala and Spark configuration in Intellij, but the result worths it!

Keep Performing,
Moshe Kaplan

    Apr 19, 2015

    5 Steps to Migrate from MySQL Community Edition to MariaDB

    Why Should You Consider the Migration?
    There are many reasons for it, but in bottom line in open source you should look for the community. 

    MySQL CE, MariaDB or Percona DB?
    Well every one should make their decisions. However, you should decide if you are looking for commercial support or community support. If you are looking for commercial support, choose the company that you most trust (and gives you the best deal).
    If you are looking for community support take a look where community is, check if the forums are active and if bugs that are being reported by the community are being taken care of. Finally search on Linkedin. It's a great way to sense where the wind blows.

    What Should You Expect?
    Faster releases, better response to community, some performance boost and in the bottom line: no change is need from your client side.

    How to Migrate?
    Migration currently is very simple, just like upgrading to a new major MySQL release:

    1. Backup:
      sudo service mysql stop
      sudo cp -R /var/lib/mysql /var/lib/mysql.old
      sudo cp -R /etc/mysql/my.cnf /etc/mysql/my.cnf.old
    2. Uninstall MySQL
      dpkg --get-selections | grep -v deinstall | grep -i mysql
      sudo apt-get purge -y percona-toolkit
      sudo apt-get purge -y php5-mysql
      sudo apt-get purge -y libmysqlclient18 mysql-client  mysql-client-5.5 mysql-client-core-5.5 mysql-common mysql-server mysql-server-5.5 mysql-server-core-5.5
    3. Install MariaDBsudo apt-get install software-properties-common
      sudo apt-key adv --recv-keys --keyserver hkp:// 0xcbcb082a1bb943db
      sudo add-apt-repository 'deb trusty main'
      sudo apt-get -y update
      sudo apt-get -y dist-upgrade
      sudo apt-get install mariadb-server mariadb-client percona-toolkit
    4. Select your root password
    5. Upgrade
      sudo mysql_upgrade -uroot -p
    That's all. You will not need to change any client or recompile them.

    Bottom Line
    Migration is easier then you may expect, now you can test and verify if it fits your needs.

    Keep Performing
    Moshe Kaplan

    Apr 4, 2015

    Modifying Your MySQL Structure w/o Downtime

    Did you try to add a new index to your MySQL huge table and suffered from a downtime?
    If the answer is positive, you should introduce yourself PT-ONLINE-SCHEMA-CHANGE.

    How the Magic is Done?
    Actually Percona imitates MySQL behavior with a little tweak.
    When modifying a table structure MySQL copies the original table structure, modifies it, copies the data and finally renames the table.
    The only problem w/ this behavior that it locks the original table...

    Percona is doing the same, but instead of locking the original table, it reviews the latest changes and implements them on the new table. That way the original table still serves the users, and changes replacement is done in a single atomic process.

    Percona Toolkit Installation
    Download the Percona toolkit and install it (the following is relevant for Ubuntu):
    > wget
    > sudo dpkg -i percona-toolkit_2.2.13_all.deb

    Making a Change
    Just call the tool with permissions, database name (D flag), table name (t flag), command to execute (--alter flag) and finally use the execute flag to implement the changes.
    pt-online-schema-change --alter "ADD COLUMN c1 INT" D=sakila,t=actor -uuser -p"password" --execute

    Things to Notice
    1. You must have a primary key on the table
    2. If you want only to verify the process before replacing the tables themselves, use --dry-run instead of execute (or just drop this parameter).

    Bottom Line
    Modifying your database will cause performance degradation, but it should not result in a downtime.

    Keep Performing,
    Moshe Kaplan


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