How to set heap size for sbt?

Question

I am using SBT 0.12.0. I have read other answers on stack overflow and followed them, however none of them helps, for example:

• create ForkRun clas

Answer 1

On windows, for sbt 0.13.9.2, you need to set JAVA_OPTS to the jvm options you want.

> set JAVA_OPTS=-Xmx1G
> sbt assembly

The sbt.bat script loads its defaults from conf\sbtconfig.txt into CFG_OPTS but will use JAVA_OPTS instead if set.

Relevant excerpts from sbt.bat:

rem FIRST we load the config file of extra options.
set FN=%SBT_HOME%\..\conf\sbtconfig.txt
set CFG_OPTS=
FOR /F "tokens=* eol=# usebackq delims=" %%i IN ("%FN%") DO (
  set DO_NOT_REUSE_ME=%%i
  rem ZOMG (Part #2) WE use !! here to delay the expansion of
  rem CFG_OPTS, otherwise it remains "" for this loop.
  set CFG_OPTS=!CFG_OPTS! !DO_NOT_REUSE_ME!
)

. . . (skip) . . .

rem We use the value of the JAVA_OPTS environment variable if defined, rather than the config.
set _JAVA_OPTS=%JAVA_OPTS%
if "%_JAVA_OPTS%"=="" set _JAVA_OPTS=%CFG_OPTS%
:run
"%_JAVACMD%" %_JAVA_OPTS% %SBT_OPTS% -cp "%SBT_HOME%sbt-launch.jar" xsbt.boot.Boot %*

Answer 2

As of March 2015, if you are using sbt on OSX with Homebrew then you should edit the file /usr/local/etc/sbtopts

e.g.

# set memory options
#
#-mem   <integer>
-mem 2048

Answer 3

I have found the solution. No matter how you specify JVM heap size, it will never work because SBT executable already has it overridden.

There is a line in SBT executable which says:

. /usr/share/sbt/sbt-launch-lib.bash

So I edited the file:

  # run sbt
  execRunner "$java_cmd" \
    ${SBT_OPTS:-$default_sbt_opts} \
-   $(get_mem_opts $sbt_mem) \
    ${java_opts} \
    ${java_args[@]} \
    -jar "$sbt_jar" \
    "${sbt_commands[@]}" \
    "${residual_args[@]}"

Remove the - line.

Now when you run SBT, it will no longer override your JVM heap size settings. You can specify heap size settings using @Noan's answer.

Or alternatively:

sbt -J-Xmx4G -J-Xms4G

Answer 4

A quick way to do it is with a .jvmopts file in the root of your project (from the Lagom Framework documentation):

 $ cat .jvmopts
 -Xms512M
 -Xmx4096M
 -Xss2M
 -XX:MaxMetaspaceSize=1024M