Database features

Feature is an interface allowing to store and query additional information based on bytecode. Feature can be installed only upon creating the JacoDB instance.

var db = JacoDb.async(new JcSettings()
    .useProcessJRE()
    .persistent("/tmp/compilation-db/${System.currentTimeMillis()}") // persist data
    .installFeatures(Usages.INSTANCE, InMemoryHierarchy.INSTANCE)
).get();

InMemoryHierarchy#

By default, JacoDB stores information about class hierarchy in an SQL database (the ClassHierarchies table with the columns: class_id, super_id, is_interface). It allows us to retrieve the hierarchy for a particular class with a recursive SQL query. Recursive queries are rather common and rather slow.

InMemoryHierarchy solves a performance problem of a built-in solution. It introduces a fast-search in-memory cache.

Memory overhead is O(number of classes). For the project with about 50K classes (including runtime) memory consumption for such a cache is ~6.5 Mb of heap memory.

Usages#

You can find places where methods and fields are used. For better performance, install InMemoryHierarchy.

var db = JacoDb.async(new JcSettings()
    .useProcessJRE()
    .persistent("/tmp/compilation-db/${System.currentTimeMillis()}") // persist data
    .installFeatures(Usages.INSTANCE, InMemoryHierarchy.INSTANCE)
).get();
var method = run; // java.lang.Runnable#run method
var field = field; // java.lang.String#value field
var cp = db.asyncClasspath(allClasspath).get();
cp.findUsages(method); // sequence of methods which calls method
cp.findUsages(field, FieldUsageMode.READ); // sequence of fields which reads field value

The Usages indexer goes through all instructions, collects information on method calls or field access, and stores it in a table: