OutOfMemoryException at DT loading

I have created DT having 20.000 rows with 4 conditions and 1 action in CSV format
and set the following parameters for JVM -Xmx3072M -XX:MaxPermSize=256M.

I haveOutOfMemoryException with the following stack trace
java.lang.OutOfMemoryError: Java heap space
at java.lang.String.format(String.java:2558)
at org.drools.lang.DroolsParserExceptionFactory.formatParserLocation(DroolsParserExceptionFactory.java:203)
at org.drools.lang.DroolsParserExceptionFactory.createErrorMessage(DroolsParserExceptionFactory.java:104)
at org.drools.lang.DroolsParserExceptionFactory.createDroolsException(DroolsParserExceptionFactory.java:89)
at org.drools.lang.DRLParser.reportError(DRLParser.java:350)
at org.antlr.runtime.BaseRecognizer.recoverFromMismatchedToken(BaseRecognizer.java:624)
at org.antlr.runtime.BaseRecognizer.match(BaseRecognizer.java:115)
at org.drools.lang.DRLParser.fact(DRLParser.java:9841)
at org.drools.lang.DRLParser.lhs_pattern(DRLParser.java:9388)
at org.drools.lang.DRLParser.pattern_source(DRLParser.java:7432)
at org.drools.lang.DRLParser.lhs_unary(DRLParser.java:6582)
at org.drools.lang.DRLParser.lhs_and(DRLParser.java:6229)
at org.drools.lang.DRLParser.lhs_or(DRLParser.java:5877)
at org.drools.lang.DRLParser.lhs(DRLParser.java:5673)
at org.drools.lang.DRLParser.normal_lhs_block(DRLParser.java:5580)
at org.drools.lang.DRLParser.when_part(DRLParser.java:3975)
at org.drools.lang.DRLParser.rule(DRLParser.java:3769)
at org.drools.lang.DRLParser.statement(DRLParser.java:993)
at org.drools.lang.DRLParser.compilation_unit(DRLParser.java:484)
at org.drools.compiler.DrlParser.compile(DrlParser.java:238)
at org.drools.compiler.DrlParser.parse(DrlParser.java:78)
at org.drools.compiler.DrlParser.parse(DrlParser.java:83)
at org.drools.compiler.PackageBuilder.addPackageFromDrl(PackageBuilder.java:275)
at org.drools.compiler.PackageBuilder.addKnowledgeResource(PackageBuilder.java:510)
at org.drools.builder.impl.KnowledgeBuilderImpl.add(KnowledgeBuilderImpl.java:31)
....

Is 3Gb not enough for such a problem?!

How may memory requirements be estimated?