Using cache and incremental builds in real world scenarios

TCI-Graphics for AdsBlogs (1)

We all want shorter builds, what are some ways we can accomplish that? In this post I’ll give you a variety of ways to help reduce build times, and overall optimization of your .travis.yml file. We’ll talk about caching and the incremental build method in Travis CI. In general and the majority, short build durations are associated with Travis builds that are configured cache content that does not change often (e.g. bash scripts, some dependency), to finish as soon as all the Travis workers finish the required jobs.

Why use incremental builds?

In short, incremental builds an approach to split builds into a set of incremental set of smaller builds in order to speed up the build generation process, in turn giving you a faster build time. So when deciding to make a Travis build have incremental hallmarks, speed of incremental builds is crucial to get a short edit-compile-test loop, thus sparing you time.

Examples of parrallel/incremental builds

In this example, I’ll be using sbt some of you may have heard of it, if not I recommend taking a peek at it. The short description of sbt is that sbt is specifically built for Scala and Java projects. It’s mainly used by developers via the ability to cross build your project against multiple Scala versions, and this is one of the reasons I personally use it. Let’s start with a .travis.yml:

language: scala

jdk: openjdk8

   - 2.10.4
   - 2.12.14

Now by default Travis will run sbt ++$TRAVIS_SCALA_VERSION test, but let’s set a conditional in the .travis.yml file that enforces this. To enforce this, we will be adding a script hook in your .travis.yml file:

   - sbt ++$TRAVIS_SCALA_VERSION test

Since this blog post is about saving time and in particular the scope of this post is Java/Scala, we will be using scripted. As I was talking about earlier so you don’t have to test and build cross platform, so let’s try another .travis.yml scenario where we utilize scripted:

language: scala

jdk: openjdk8

   - sbt scripted

I recommend making these type of “time-saving” builds as verbose as possible, in the build log you’ll see the following lines:

export JVM_OPTS=@/etc/sbt/jvmopts
export SBT_OPTS=@/etc/sbt/sbtopts

You’ll then learn what env vars are being passed where. In turn giving you a garden variety ways of saving time.


Caching in Travis CI is always a crucial way to speed up build times. In this example we’re even going to cut unnecessary cache updates if you wish to even speed your build times up even further. So what we can do is use the before_cache: hook, and use the rm command which means `remove. Let’s give you an exmaple:

- rm -fv $HOME/.ivy2/.sbt.ivy.lock
- find $HOME/.ivy2/cache -name "ivydata-*.properties" -print -delete
- find $HOME/.sbt -name "*.lock" -print -delete
- echo "We saved time"

Now let’s actually use the cache hook. When using sbt depending on what os you’re building on, the directories could change, so please be cognizant of this:

- $HOME/.cache/coursier
- $HOME/.ivy2/cache
- $HOME/.sbt

This usually will take on average ~3-4 minutes off your build time using cache whilst using this in conjunction with the before_cache script hook.

Using Bash

We talked about sbt above and Scala but let’s look at broader scope of improving build times. One of the tools I use is bash, to some degree it helps us automate things, which in itself is a time saver. So let’s create variables for a frequently-referenced file in paths and branches:

export branch=$TRAVIS_BRANCH

One thing I’ve noticed is ensuring that inexact rename detection error isn’t skipped due to too many files is a common cause (from my own experience) for slower builds, so lets set the renameLimit in git:

git config --global diff.renameLimit 9999999

Another way we can save time is by running a git diff for the incremental build depending on the checked-out branch at the time:

if [ "$BRANCH" == "dev" ]; then
  echo 'Preparing for an incremental deployment'
  for branch in $(git branch -r|grep -v HEAD); do
    #create tracking branch:
    git checkout -qf ${branch#origin/}
  git checkout (branch name)
 # Let's run the git diff I mentioned above
  git diff --diff-filter=UMA --name-only master force-app/ |
  while read -r file; do
    # Copy the files from git diff into the deploy directory:
    sudo cp --parents "$file" $DEPLOYDIR 2>/dev/null
    # For any changed class, trigger, page file, it's associated meta-data from the parent file is copied to the deploy directory (and vice versa):
    if [[ $file == *.cls ]]; then
      find $classPath -samefile "$file-meta.xml" -exec sudo cp --parents -t $DEPLOYDIR {} \;
    elif [[ $file == *.cls-meta.xml ]]; then
      find $classPath -samefile "$parsedfile.cls" -exec sudo cp --parents -t $DEPLOYDIR {} \;
    elif [[ $file == *Test.cls ]]; then
      find $classPath -samefile "$file-meta.xml" -exec sudo cp --parents -t $DEPLOYDIR {} \;
    elif [[ $file == *Test.cls-meta.xml ]]; then
      find $classPath -samefile "$parsedfile.cls" -exec sudo cp --parents -t $DEPLOYDIR {} \;
    elif [[ $file == *.trigger ]]; then
      find $triggerPath -samefile "$file-meta.xml" -exec sudo cp --parents -t $DEPLOYDIR {} \;
    elif [[ $file == *.trigger-meta.xml ]]; then
      find $triggerPath -samefile "$parsedfile.trigger" -exec sudo cp --parents -t $DEPLOYDIR {} \;
    elif [[ $file == *.page ]]; then
      find $pagesPath -samefile "$file-meta.xml" -exec sudo cp --parents -t $DEPLOYDIR {} \;
    elif [[ $file == *.page-meta.xml ]]; then
      find $pagesPath -samefile "$" -exec sudo cp --parents -t $DEPLOYDIR {} \;


We can of course name that bash file anything we want, e.g., of course make it executable via: chmod u+x (or whatever you decide to call your bash script.)

So let’s say you have a C++ project, you have a project where a directory is cached, we know that $CACHED_DIR is the directory with the build files. So then before you start building, add a command that uses this information to fix the mtimes of the files that were changed since the previous commit:

read PREVIOUS_GIT_COMMIT < $CACHED_DIR/previous_git_commit.txt
changed_files=`git diff --name-only $PREVIOUS_GIT_COMMIT HEAD` 
touch `echo $changed_files`

Last thing I’ll add for Bash is mtime. Let’s choose a directory name the json cache (for example .mtime_cache) and add it to your .gitignore. Then add it to your Travis CI cache. Then your cache section in .travis.yml might look like this:

  - my/build/dir
  - .mtime_cache


I demonstrated ways you can save time in your builds in Scala using sbt, C++ utilizing mtime, various Travis technologies and existing technologies like Bash. This is the tip of the iceberg of ways you can save time on builds. In the time coming I will be creating a comprehensive guide on saving time on your Travis CI builds. Be on the lookout for that, it’ll be coming soon.

In the time benig, if you have any questions please email me at, with the header “Montana Mendy TCI Blog”. Happy building!