How to increase memory footprint of SQLDeveloper

Adding

AddVMOption  -Xmx1024M 
AddVMOption  -Xms512M

only to sqldeveloper/ide/bin/ide.conf may not work. It's also not recommended(please see comments on the top of the sqldeveloper\ide\bin\ide.conf file). In newer version of SQL developer(for sure after version 4.x) the settings in sqldeveloper/ide/bin/ide.conf can be overridden in

WINDOWS:

C:\Users\${WINDOWS_USER_NAME}\AppData\Roaming\sqldeveloper\${SQL_DEVELOPER_VERSION}\product.conf

LINUX:

/home/${USER_NAME}/.sqldeveloper/${SQL_DEVELOPER_VERSION}/product.conf

Note: You can find path to product.conf file in SQLDeveloper->Help->About->Properties ->Propertie name "user.conf"

You need to change

AddVMOption  -Xmx1024M 
AddVMOption  -Xms512M

in configuration files above.

Edit your sqldeveloper/ide/bin/ide.conf file and change the following two lines:

#
# If you are getting the 'Low Memory Warning' Message Dialog while running
# JDeveloper, please increase the -Xmx value below from the default 768M to
# something greater, like 1024M or 1250M.  If after increasing the value,
# JDeveloper is no longer starting up because it fails to create a virtual
# machine, then please reduce the modified -Xmx value.
#
AddVMOption  -Xmx1024M
AddVMOption  -Xms512M

The other answer regarding use of -XX:MaxPermSize in sqldeveloper/bin/sqldeveloper.conf is outdated and would not work in the recent versions of sqldeveloper. Using that would result in following sqldeveloper message on startup:

Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=1024M; support was removed in 8.0

This post has useful details on where to tweak the JVM settings.

Essentially, look for ~/sqldeveloper/bin/sqldeveloper.conf and in that, look for:

AddVMOption -XX:MaxPermSize=128M