stateful_functions

README

Stateful function examples using the generic iterator

inspired by Apache Flink

stateful function shows how the iterator framework can help to build more advanced tooling.

Example breakdown

Serial baseline

see server_baseline.go

this version server every request in the serial mode

Multi workers

see server_workers.go

this version uses multiple goroutines (NumWorkers) to process the requests hence faster than the serial version; its performance is far less ideal due to every read and write goes through a mutex.

Bad stateful function implementation

see server_bad_stateful.go

this version tries to solve the mutex issue by introducing a local state to each worker;

each worker stores the processing result (mutating the global state - a "state delta") in its local state and moves on to process the next request;

it is completely useless as the state deltas are not merged back to the global state;

it does show a dramatic improvement of speed due to the complete elimination of mutex;

Ok stateful function implementation

see server_ok_stateful.go

this version introduces a "merging" solution that periodically merge the local state that holds the global state delta, back to the global store.

the frequency of merging is parameterized (called the MergeTicks) and can be tuned;

it shows if the frequency is high - leading to better state consistency - the performance is low; and if the frequency is low - leading to potential errors due to state inconsistency - the performance can be high

in this very limited example:

ticks(30), low freq   6x speedup
ticks(10), high freq  4x speedup
ticks(4), e-high freq 2x speedup

Thought

there are a few variations of the local state and the merger algorithms:

• use append-only logs for the local state and snapshots for the global state
• use tiered merge frequency as certain properties are less important and can be inconsistent to some extent
• partition the global state and snapshot each partition instead of the entire global state
• use append-only logs for both the local state and the global state; introduce a log-view for read-access only