Threading
=========

CCF allows for commands to be executed on multiple threads.
This is done to increase transaction throughput while attempting to limit the effect on transaction latency.

Consistency
-----------

If all commands are executed on the primary, CCF guarantees session consistency from the perspective of a :term:`TLS` client connection.
This means that within a single client connection a client is guaranteed to read its own writes.
For example, if a client sends command (A) to the primary of a CCF service and then sends command (B), CCF guarantees that command (A) will be executed before command (B).

Implementation
--------------

Configuration
~~~~~~~~~~~~~

To enable multiple worker threads, the ``worker_threads`` configuration option can be used  along with the number of desired threads to ``cchost`` when starting a CCF node.

It is strongly recommended that all CCF nodes run the same number of worker threads.
The number of worker threads must be at least 1 less than the value of ``NumTCS`` in the oe_sign.conf file.

Programming Model
~~~~~~~~~~~~~~~~~

To ensure session consistency all commands that originate from the same connection are executed on the same thread.
It is strongly advised that during the execution of a command the application does not mutate any global state outside of the key-value store.
Any inter-command communication must be performed via the key-value store, to ensure that CCF can rollback commands or change the primary as required.