Modules

Tremor-query supports nested namespaces or modules.

Modules in tremor are the lowest unit of compilation available to developers to modularise tremor logic across multiple logical namespaces. On the filesystem, modules are rooted at a base path and are nested with folders.

Within a file, nesting is via the mod clause.

Modules can use trickle definitions via the define clause variants to define windows, operators or scripts for reuse, or nested mod sub-modules.

Module Path

Modules can be defined physically on the file system. For example given the following modular hierarchy on the file system, relative to a root module path: Nested modules can be defined as follows:

  +-- foo
    +-- bar
      +-- snot.trickle
    +-- baz
      +-- badger.trickle

The same modular hierarchy can be defined as nested module declarations as follows:

mod foo with
  mod bar with
    define tumbling window second with
      interval = 1000
    end;
  end;
  mod baz with
    define tumbling window minute with
      interval = 60000
    end;
  end;
end;

select event
from in[snot::second, badger::minute] # use our imported window definitions
into out;

Assuming this module hierarchy is rooted at /opt/my-project/lib they can be registered with tremor by prepending this folder to the TREMOR_PATH environment variable

export TREMOR_PATH="/opt/my-project/lib:$TREMOR_PATH"

Defaults

The TREMOR_PATH uses ':' on linux/unix to separate multiple module paths.

The default places to look for your modules is /usr/local/share/tremor if TREMOR_PATH is not provided.

The default place for the tremor standard library is /usr/share/tremor/lib, so the full TREMOR_PATH default is

• /usr/local/share/tremor
• /usr/share/tremor/lib

Referencing Modules with use

Modules can be loaded via the use clause which in turn loads a module from the physical file system via the module path:

use foo::bar::snot; # snot is a ref to 'foo/bar/snot.trickle'
use foo::baz::badger; # badger is a ref to 'foo/bar/badger.trickle'

select event
from in[snot::second, badger::minute] # use our imported window definitions
into out;

Inline and externalized modules can be used separately or together as appropriate.

Where there are existing references a module can be aliased to avoid clashes in the local scope:

use foo::bar as fleek;

select event
from in[fleek::second] # use our imported window definitions
into out;

It is to be noted that inclusion via use will prevent circular inclusion as in file a.trickle can use b.trickle but beyond that point b.trickle can no longer use a.trickle as this would create a dependency cycle. This is a restriction of the current implementation and may or may not be relaxed in the future.