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Persistence Module

This document is meant to be a supplement to the living protocol specification at 1.0 Pocket's Persistence Specification primarily focused on the design, implementation and testing details.

Database Migrations

Node Configuration

The config specification can be found at persistence_config.proto, and an example can be found at config1.json.

Note that the node_schema parameter MUST be unique for each node pointing to the same Postgres instance. There is currently no check or validation to guarantee this.

  "persistence": {
    // ...
    "node_schema": "node1",
    // ...
  },

Debugging & Development

Code Structure

persistence         # Directly contains the persistence module interface for each actor
├── docs
│   ├── CHANGELOG.md    # Persistence module changelog
│   ├── README.md       # Persistence module README
├── account.go
├── application.go
├── block.go
├── context.go      # Postgres context logic
├── debug.go        # For temporary LocalNet
├── db.go           # Helpers to connect and initialize the Postgres database
├── fisherman.go
├── genesis.go      # Populate genesis logic
├── gov.go
├── module.go       # Implementation of the persistence module interface
├── servicer.go
├── shared_sql.go   # Database implementation helpers shared across all protocol actors
└── validator.go
├── docs
├── kvstore         # Key value store for database
├── proto           # Proto3 message files for generated structures
│   ├── account.proto   # account structure
│   ├── actor.proto     # protocol actor structure (e.g. validator, servicer, etc...)
│   ├── config.proto    # configuration structure
│   ├── gov.proto       # params structure
│   ├── state.proto     # genesis state structure
├── types           # Directly contains the SQL schema and SQL query builders used by the files above
│   ├── migrations
│   ├── account.go
│   ├── application.go
│   ├── base_actor.go            # Implementation of the `protocol_actor.go` interface shared across all actors
│   ├── block.go
│   ├── fisherman.go
│   ├── gov.go
│   ├── persistence_genesis.go   # Implements shared genesis interface
│   ├── protocol_actor.go        # Interface definition for the schema shared across all actors
│   ├── servicer.go
│   ├── shared_sql.go            # Query building implementation helpers shared across all protocol actors
│   └── unstaking.go             # Implements shared unstaking interface
│   └── util.go
│   └── validator.go
└── test  # Unit & fuzzing tests

Makefile Helpers

Running make from the root of the pocket repo will show several targets prefixed with db_ to help with the design, development & debugging of this module.

A subset of these are explained below.

Populating the database

Any targets or helpers to configure and launch the database instances do not populate the actual database.

A LocalNet (see make compose_and_watch) must have been executed in order to trigger creation of schemas and hydration of the relevant tables.

CLI Access - db_cli_node

Open up a CLI to the postgres database via:

make db_cli # Connect to the DB before connecting to a specific schema
# OR
psqlSchema=node3 make db_cli_node # Immediately connect to the schema of node3

Then you can make use of the following SQL commands and explore:

SELECT schema_name FROM information_schema.schemata; // View all of the schemas available
SET search_path=node1; // Set the search path to a schema `node1`
/dt // View all available tables

Admin View - db_admin

Running make db_admin should echo the following to your terminal:

echo "Open http://0.0.0.0:5050 and login with '[email protected]' and 'pgadmin4'.\n The password is 'postgres'"

If the pgadmin configs in our docker-compose file do not automatically bind, you might need to configure the server yourself as seen in the image below (you will also need to set a name in the General tab):

Postgres' admin configuration

The following screenshot shows where the tables for each schema can be found:

Postgres' admin view of LocalNet tables & schemas

Benchmarking - db_bench

TODO: Build on top of make db_bench to enable a proper suite for benchmarking the node

Testing

Unit Tests - All

Unit tests can be executed with:

make test_persistence

Unit Tests - State Hash

Unit tests can be executed with:

make test_persistence_state_hash

Dependencies

We use dockertest to configure a local Postgres Docker Daemon during unit testing.

Setup

Make sure you have a Docker daemon running. See the Development Guide for more references and links.

Setup Issue - Docker Daemon is not Running

not start resource: : dial unix /var/run/docker.sock: connect: no such file or directory

Double check your Docker Daemon is running. For example, on macOS, you can run:

open /Applications/Docker.app

Setup Issue - Port already allocated

Bind for 0.0.0.0:5432 failed: port is already allocated

Double check you don't already have a Postgres docker container running on your host machine. For example, on macOS, you can run:

lsof -i:5432

And kill the relevant process if one exists.

[OUTDATED]Implementation FAQ

NOTE: This section has not been reviewed/updated in a while and will nee to be re-reviewed by someone on the core team.

Q: Why do Get methods (e.g. GetAccountAmount) not return 0 by default? A: This was done intentionally to differentiate between accounts with a history and without a history. Since accounts are just a proxy into a public key, they all "exist by default" in some senses.

Q: Why are amounts strings? A: A lesson from Tendermint in order to enforce the use of BigInts throughout and avoid floating point issues when storing data on disk.

Q: Why not use an ORM? A: We are trying to keep the module small and lean initially but are ope

Q: What is a Param in the Gov schema? A: It represents a value associated with a name and a height that we can reference to represent governance settings. These settings have the power of altering the behaviour of various aspects of the network.

Q: What is a Flag in the Gov schema? A: A flag is very much alike a Param with the difference that it also has a boolean flag to specify if that setting is enabled or not at any point in time (height). We are discussing if we should replace the boolean flag and allow multivariate feature flags.

[OUTDATED] Implementation TODOs

NOTE: This section has not been reviewed/updated in a while and will nee to be re-reviewed by someone on the core team.

These are major TODOs spanning the entire repo so they are documented in one place instead.

Short-term (i.e. simpler starter) tasks:

  • DOCUMENT: Need to do a better job at documenting the process of paused apps being turned into unstaking apps.
  • CLEANUP: Remove unused parameters from the PostgresContext interface (i.e. see where _ is used in the implementation such as in InsertFisherman)
  • IMPROVE: Consider converting all address params from bytes to string to avoid unnecessary encoding
  • CLEANUP(#76): Review all the gov_*.go related files and simplify the code
  • REFACTOR/DISCUSS: Should we prefix the functions in the PersistenceModule with the Param / Actor it's impacting to make autocomplete in implementation better?
  • DISCUSS: Consider removing all Set methods (e.g. SetAccountAmount) and replace with Add (e.g. AddAccountAmount) by having it leverage a "default zero".
  • REFACTOR(pokt-network#102): Split account and pool into a shared actor (e.g. like fisherman/validator/servicer/application) and simplify the code in half
  • CLEANUP: Remove tokens or stakedTokens in favor of using amount everywhere since the denomination is not clear. As a follow up. Consider a massive rename to make the denomination explicit.

Mid-term (i.e. new feature or major refactor) tasks:

  • IMPROVE: Consider using prepare statements and/or a proper query builder
  • TODO(pokt-network#77): Implement proper DB SQL migrations
  • INVESTIGATE: Benchmark the queries (especially the ones that need to do sorting)
  • DISCUSS: Look into address is being computed (string <-> hex) and determine if we could/should avoid it

Long-term (i.e. design) tasks

  • INVESTIGATE: Expand the existing fuzzing approach to push random changes in state transitions to its limit.
  • INVESTIGATE: Use a DSL-like approach to design complex "user stories" for state transitions between protocol actors in different situations.